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File: Nutritional Epidemiology Pdf 135185 | Nutritionreviews59 0349
november 2001 349 357 zyxwvutsrqponmlkjihgfedcbazyxwvutsrqponmlkjihgfedcba lead review article zyxwvutsrqponmlkjihgfedcbazyxwvutsrqponmlkjihgfedcba physical activity and cancer lessons learned from nutritional epidemiology zyxwvutsrqponmlkjihgfedcbazyxwvutsrqponmlkjihgfedcba christine m friedenreich ph d downloaded from https academic oup com ...

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                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     November 2001: 349-357 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA
                                                                                                              Lead Review Article zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA
                                                                                                             Physical Activity and Cancer: Lessons Learned from 
                                                                                                            Nutritional Epidemiology zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA
                                                                                                             Christine M. Friedenreich, Ph.D. 
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  Downloaded from https://academic.oup.com/nutritionreviews/article/59/11/349/1827811 by guest on 04 January 2023
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    State of Scientific Evidence for Physical Activity 
                                                                                                            Convincing epidemiologic evidence currently ex- 
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    in Cancer Etiology 
                                                                                                           ists  for  an association between physical activity 
                                                                                                           and the prevention of  colon and breast cancer. 
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   A comprehensive review of the epidemiologic literature 
                                                                                                           Physical activity may also reduce the risk of  can- 
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    on physical activity and cancer prevention was recently 
                                                                                                           cer at several other sites. With increasing research 
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    conducted.'  That review used the classifications for sci- 
                                                                                                           on this topic, it is apparent that studies of physical 
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    entific evidence that had been developed by the panel of 
                                                                                                          activity and cancer have numerous methodologi- 
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    scientists who wrote the report of the World Cancer Re- 
                                                                                                           cal similarities with studies of  nutrition and can-                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     search Fund/American Cancer Institute for Research on zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA
                                                                                                           cer. Lessons learned from nutritional epidemiol-                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        Food, Nutrition and the Prevention zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBAof  Cancer: A zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBAGlobal 
                                                                                                          ogy that can be applied to studies of physical ac- 
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   Perspective.2 Briefly, four categories for scientific evidence 
                                                                                                          tivity and cancer prevention and recommendations 
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   were defined. Convincing evidence exists when consis- 
                                                                                                          for  future research are discussed in this review. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   tent associations are reported in at least 20 studies con- 
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    ducted worldwide that used different study designs, that 
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    showed dose-response relationships, that are biologically 
                                                                                                            Introduction 
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   plausible, and for which laboratory evidence is also sup- 
                                                                                                          Whereas evidence of a role of physical activity in cancer 
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   portive of the association. Probable evidence exists when 
                                                                                                           etiology has accumulated rapidly, particularly in the last 
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    consistent associations are found in less than 20 studies 
                                                                                                          decade, there are numerous methodological limitations to 
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    conducted worldwide, using different study designs, 
                                                                                                           studies in this area. The field of physical activity and can- 
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    when biologic plausibility is likely, and some supportive 
                                                                                                           cer epidemiology has many similarities to nutrition and 
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     laboratory evidence exists. Possible evidence exists when 
                                                                                                          cancer epidemiology, and numerous lessons learned in 
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    there are generally supportive studies; however, they are 
                                                                                                          nutrition and cancer research are directly applicable to 
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     limited in quantity, quality, or consistency, and laboratory 
                                                                                                          physical activity and cancer. During the past 30 years, 
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    evidence may not exist. Insufficient evidence exists when 
                                                                                                          considerable advances in dietary assessment methods and 
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    there are only a few studies that are generally consistent 
                                                                                                           studies of nutrition and cancer have been achieved through 
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    but more research is needed because there is simply not 
                                                                                                          the collaboration of nutritionists, epidemiologists, and 
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     enough evidence to make any conclusions about the as- 
                                                                                                          biostatisticians. For comparable advances to be achieved 
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     sociation. 
                                                                                                          in physical activity and cancer research, similar 
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               Applying these definitions to the literature on physi- 
                                                                                                          multidisciplinary collaborations are needed between exer- 
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    cal activity and cancer prevention, it was concluded that 
                                                                                                          cise physiologists, epidemiologists, cancer biologists, and 
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    there is convincing  evidence that physical activity re- 
                                                                                                          biostatisticians. The objective of this review is to high- 
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    duces colon and breast cancer, whereas the evidence for 
                                                                                                          light the state of evidence for physical activity and can- 
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    prostate cancer is probable, evidence is possible for lung 
                                                                                                          cer, outline the methodological issues and gaps in knowl- 
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     and endometrium cancers, and evidence is still insufi- 
                                                                                                          edge that remain, and suggest how advances can be 
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     cient to make any judgement for the remaining cancer 
                                                                                                          achieved in this field by adapting methods and knowl- 
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     sites.' Table 1 summarizes the literature by listing the main 
                                                                                                          edge gained in nutrition and cancer epidemiology. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      findings from this body of literature. The key features 
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      listed include: 1) the number of studies that showed a risk 
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     reduction among the most physically active study sub- 
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   jects as compared with the least active participants (i.e., 
                                                                                                                                                      Dr.  Friedenreich  is  with  the  Division  of 
                                                                                                           Epidemiology, Prevention and Screening, Alberta                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           the consistency of the association);  2) the average risk 
                                                                                                           Cancer Board, Calgary, Alberta, Canada, T2N 4N2.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           reduction found in these studies (i.e., the strength of the 
                                                                                                          Nutrition Reviews@, Vol. 59, No. 11                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       349 
                                                      Table 1. Summary zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBAof Epidemiologic Evidence on the Association between Physical Activity and Cancer by 
                                                      Criteria for Causalitv zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA
                                                                                                                  Consistency of                                                                          Strength of 
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           Overall 
                                                                                                                        Association                                                                     Association                                                              Dose-ResDonse 
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           Level of 
                                                                                                                           Number of                                                                Average Risk                                                                                  Number                                                                  Hypothesized                                                                                                                                                     Scientific 
                                                                                                                                                                                                                                                                                                                                                                          Biologic Mechanisms                                                                                                                                              Evidence zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA
                                                      Cancer Site                                                                 Studies                                                                   Reduction                                                                         of Studies 
                                                      Colon                                                                       39 of46                                                                         4&50%                                                                            23 of 29                                                               Decreased gastrointestinal                                                                                                                                       Convincing 
                                                                                                                                                                                                                                                                                                                                                                          transit time, decreased ratio of 
                                                                                                                                                                                                                                                                                                                                                                          prostaglandins (PGEPGF), 
                                                                                                                                                                                                                                                                                                                                                                          lowered bile acid secretion or 
                                                                                                                                                                                                                                                                                                                                                                          enhanced metabolism, decreased 
                                                                                                                                                                                                                                                                                                                                                                          percent body fat,* decreased 
                                                                                                                                                                                                                                                                                                                                                                          circulating insulin and glucose,                                                                                                                                                                                                                               Downloaded from https://academic.oup.com/nutritionreviews/article/59/11/349/1827811 by guest on 04 January 2023
                                                                                                                                                                                                                                                                                                                                                                          * exercise-induced increase in 
                                                                                                                                                                                                                                                                                                                                                                          antitumor immune defences, 
                                                                                                                                                                                                                                                                                                                                                                          * improved antioxidant defence 
                                                                                                                                                                                                                                                                                                                                                                          systems,* genetic predisposition 
                                                                                                                                                                                                                                                                                                                                                                          of habitually active* 
                                                     Breast                                                                      25 of36                                                                          3040%                                                                             15 of22                                                               Decreased lifetime exposure                                                                                                                                       Convincing 
                                                                                                                                                                                                                                                                                                                                                                          to estrogen 
                                                     Prostate                                                                      14of25                                                                          1 &30%                                                                           lOofl8                                                                Reduced exposure to testosterone  Probable 
                                                                                                                                                                                                                  3wo% zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA5 of7                                                                                          Possible decreased exposure to                                                                                                                                    Possible 
                                                     Lung                                                                             60f8 
                                                                                                                                                                                                                                                                                                                                                                          inhaled carcinogens with 
                                                                                                                                                                                                                                                                                                                                                                          increased pulmonary hnction 
                                                     Endometrium                                                                    8 of 12                                                                       3040%                                                                                 4of7                                                              Decreased lifetime exposure to                                                                                                                                    Possible 
                                                                                                                                                                                                                                                                                                                                                                          estrogen, decreased circulating 
                                                                                                                                                                                                                                                                                                                                                                          insulin and glucose 
                                                     Testicles                                                                         3 of8                                                                              20%                                                                           3 of5                                                             Trauma to testes? Influence on                                                                                                                                    Insufficient 
                                                                                                                                                                                                                                                                                                                                                                          androgens and gonadotrophins? 
                                                                                                                                                                                                                                                                                                        2 of3                                                             Decreased number of lifetime                                                                                                                                      Insufficient 
                                                     Ovaries                                                                           20f5 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBAo?? 
                                                                                                                                                                                                                                                                                                                                                                           ovulatory cycles, decreased ratio 
                                                                                                                                                                                                                                                                                                                                                                          of prostaglandins (PGEPGF) 
                                                      * These mechanisms are equally applicable to all cancer sites. 
                                                     association); 3) the number of studies that found that risk                                                                                                                                                                                                                                of the identified methodologic weaknesses in the extant 
                                                     of cancer decreased linearly as the level of physical activ-                                                                                                                                                                                                                               literature. These weaknesses include the crude and impre- 
                                                                                                                                                                                                                                                                                                                                                cise measures of physical activity, the lack of 
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              full assess- 
                                                     ity increased (i.e., the dose-response zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBArelation); 4) the un- 
                                                     derlying hypotheses that might explain the reasons for                                                                                                                                                                                                                                    ment and control for confounding factors including di- 
                                                     the association (i.e., the biologic plausibility of the asso-                                                                                                                                                                                                                              etary intake, the lack of consideration of effect modifica- 
                                                     ciation); and 5) the overall classification for the evidence                                                                                                                                                                                                                               tion by other factors, and the lack of understanding of the 
                                                     for this association.                                                                                                                                                                                                                                                                     underlying biologic mechanisms that may be operative in 
                                                                         Based on this review of the literature,' it was argued                                                                                                                                                                                                                 these associations.'  Hence, more research is needed to 
                                                     that sufficient evidence has accumulated from observa-                                                                                                                                                                                                                                     confirm the etiologic role for physical activity in cancer 
                                                     tional epidemiologic studies regarding the association                                                                                                                                                                                                                                     prevention in most cancer sites before intervention stud- 
                                                     between physical activity and colon and breast cancer to                                                                                                                                                                                                                                   ies can be conducted. 
                                                     warrant commencing intervention studies of physical ac-                                                                                                                                                                                                                                                        For faster progress to be made in the field of physical 
                                                     tivity  for those two cancer sites. The outcome of these                                                                                                                                                                                                                                   activity and cancer prevention, it is also prudent to learn 
                                                     intervention studies would be more precise information                                                                                                                                                                                                                                     from progress made in the field of nutrition and cancer 
                                                     on the exact timing and dose of physical activity required                                                                                                                                                                                                                                 prevention because of the similarities between the disci- 
                                                     for cancer risk reduction. At present, sufficient evidence                                                                                                                                                                                                                                 plines and the common and overlapping biologic models 
                                                      exists to have general public health recommendations to                                                                                                                                                                                                                                   for the influence of these lifestyle factors on carcinogen- 
                                                     increase physical activity in order to reduce cancer risk;                                                                                                                                                                                                                                 esis. The next section highlights methodological  issues 
                                                     however, insufficient evidence exists to formulate more                                                                                                                                                                                                                                    that are common to both fields and areas for hture progress 
                                                     precise activity prescriptions for the general population.                                                                                                                                                                                                                                 and collaboration. 
                                                                         For the remaining cancer sites, there is insufficient                                                                                                                                                                                                                   Methodological Issues and Solutions in 
                                                      evidence at present to justify cancer prevention interven-                                                                                                                                                                                                                                 Nutritional Epidemiology 
                                                     tion trials of physical activity. Rather, additional observa- 
                                                     tional epidemiologic studies are needed that address some                                                                                                                                                                                                                                   In both nutritional and physical activity epidemiologic zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA
                                                      350                                                                                                                                                                                                                                                                                                                                                                                             Nutrition Reviews@, Vol. 59, No. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA11 
                                                    studies, the complexity of the exposures and the correla-                                                                                                                                                                                                                             and that are of heterogeneous origins. One example 
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               is the 
                                                    tions between the exposures and other behaviors must be                                                                                                                                                                                                                               European Investigation in Cancer and Nutrition prospec- 
                                                    considered  in  the collection and analysis of data.3 Be-                                                                                                                                                                                                                            tive cohort study5 that has as one of its main objectives to 
                                                    cause each type of epidemiologic study available for the                                                                                                                                                                                                                              overcome the problem of homogeneous exposures and 
                                                    investigation of diet or physical activity and cancer asso-                                                                                                                                                                                                                           study populations. This study will compare and combine 
                                                   ciations has both strengths and some major limitations,                                                                                                                                                                                                                                data from ten European countries where the populations 
                                                   no one study design or method of data collection is con-                                                                                                                                                                                                                              have very different dietary habits. Future multicentered 
                                                   sidered definitive. Observational epidemiologic studies                                                                                                                                                                                                                                cohort studies of physical  activity are needed that in- 
                                                   of diet and physical activity have several advantages when                                                                                                                                                                                                                             clude diverse populations with heterogeneous  activity 
                                                   compared with intervention trials, including the ability to                                                                                                                                                                                                                            levels and different ethnic and racial origins. Such large- 
                                                   examine exposures that would be difficult to assign ex-                                                                                                                                                                                                                                scale studies that have sufficient statistical power could 
                                                   perimentally and the ability to assess effects of exposures                                                                                                                                                                                                                           then compare and contrast the effects of physical activity                                                                                                                                                                                                                               Downloaded from https://academic.oup.com/nutritionreviews/article/59/11/349/1827811 by guest on 04 January 2023
                                                   in free-living populations over a long time period. Obser-                                                                                                                                                                                                                             on disease risk for these different ethnic and racial groups. 
                                                   vational studies of diet and physical activity also have a 
                                                   number of key limitations that need to be considered when                                                                                                                                                                                                                             Data Collection Methods 
                                                   assessing the results of these studies. Measurement of                                                                                                                                                                                                                                 The second methodological issue is related to the type of 
                                                   dietary intake and physical activity share numerous meth-                                                                                                                                                                                                                              data collection methods and their validity and reliability. 
                                                   odological challenges. Both are complex exposures that                                                                                                                                                                                                                                 Many dietary assessment methods have been developed 
                                                   have several components that change during a study                                                                                                                                                                                                                                     for different purposes. These methods include 24-hour 
                                                  participant’s lifetime, and that require current databases                                                                                                                                                                                                                              recalls, 7-day weighed food records, food-frequency ques- 
                                                  to estimate accurately either the energy and nutrient in-                                                                                                                                                                                                                               tionnaires,  and diet history questionnaires. Dietary as- 
                                                  take or the energy expenditure.                                                                                                                                                                                                                                                         sessment methods are constantly undergoing  improve- 
                                                                      Nine of the main methodological issues of observa-                                                                                                                                                                                                                  ment and many of the methods used to develop and im- 
                                                  tional epidemiologic studies that have been encountered                                                                                                                                                                                                                                 prove these instruments can be directly applied to the 
                                                  in nutritional epidemiology and that have direct relevance                                                                                                                                                                                                                              development of physical  activity assessment methods. 
                                                  to physical activity epidemiology are homogeneity in popu-                                                                                                                                                                                                                              For example, food-frequency questionnaires were devel- 
                                                  lation sampling, validity and reliability of the data collec-                                                                                                                                                                                                                           oped from the analysis of 24-hour recalls, weighed food 
                                                  tion instruments, measurement error problems, accuracy                                                                                                                                                                                                                                  records, and dietary survey data. On this basis, the most 
                                                  and completeness of databases, lack of consideration of                                                                                                                                                                                                                                 commonly consumed food items were selected and in- 
                                                  dietary and lifestyle patterns, confounding, effect modifi-                                                                                                                                                                                                                             cluded in the food-frequency questionnaires. A compa- 
                                                  cation, appropriate statistical methods, and elucidation 
                                                                                                                                                                                                                                                                                                      of                                  rable approach can be applied to the development of physi- 
                                                  biologic mechanisms. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBAcal activity questionnaires. Data on the most commonly 
                                                                                                                                                                                                                                                                                                                                          reported activities could be compiled and these activities 
                                                  Population Sampling Methods                                                                                                                                                                                                                                                             used when preparing lists of activities that study respon- 
                                                  The first methodological issue is the range of exposure                                                                                                                                                                                                                                 dents report. In addition, substantial research has been 
                                                  within the study population. Nutritional  epidemiologic                                                                                                                                                                                                                                 undertaken in nutritional epidemiology to estimate the 
                                                  studies have often been conducted within populations                                                                                                                                                                                                                                    validity  and reliability  of dietary assessment  methods, 
                                                  that have very homogeneous exposures. Furthermore,                                                                                                                                                                                                                                      whereas far less research has determined the psychomet- 
                                                  there have frequently been insufficient numbers of study                                                                                                                                                                                                                                ric properties  of physical activity assessment methods. 
                                                  subjects with very low or very high intakes to investigate                                                                                                                                                                                                                              Clearly, an important area of hture consideration in physi- 
                                                  the influence of exposures at these levels. It is possible,                                                                                                                                                                                                                             cal activity epidemiology is to establish and ensure the 
                                                  for example, that a threshold exists for the effect of certain                                                                                                                                                                                                                          reliability and validity of the data collection instruments 
                                                  macronutrients (e.g., fat) on tumor promotion and that the                                                                                                                                                                                                                              being used. 
                                                  lowest percentage of fat intake among individuals or groups 
                                                  in any particular study population is higher than the thresh-                                                                                                                                                                                                                           Measurement Error Problems 
                                                  old.4 The range of intakes within study populations may                                                                                                                                                                                                                                 The third methodological issue addressed in nutritional 
                                                  therefore  have been too narrow to detect associations                                                                                                                                                                                                                                  epidemiologic studies is the systematic and random er- 
                                                  that do exist. A zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBArelated issue is the ethnic and racial com- 
                                                                                                                                                                                                                                                                                                                                          rors that occur in dietary asse~sment.~.~ One source of 
                                                  position of the study sample. Epidemiologic studies have                                                                                                                                                                                                                                random error in dietary intake is the natural variation in 
                                                  too frequently been conducted within one ethnic or racial                                                                                                                                                                                                                               daily eating patterns.* Dietary assessment methods that 
                                                  group, thereby limiting the generalizability of the results.                                                                                                                                                                                                                            inquire about intake over a relatively extended time period 
                                                                      These limitations are being overcome in nutritional                                                                                                                                                                                                                 attempt to decrease to a minimum the random error attrib- 
                                                  epidemiology by conducting studies in several centers or                                                                                                                                                                                                                                utable to daily fluctuations in intake and activity. These 
                                                  among populations that have heterogeneous  exposures                                                                                                                                                                                                                                    assessment methods can also introduce systematic error, zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA
                                                  Nutrition Reviews@, Vol. 59, No. 11 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       35 1 
                                                                            however, because study subjects may under- or over-re-                                                                                                                                                                                                                                                                                                                                                               the sources of random and systematic error and by ana- 
                                                                            port their intake or activity. Some incorrect reporting may                                                                                                                                                                                                                                                                                                                                                          lyzing measurement errors as has been done in nutritional 
                                                                           be intentional (e.g., overweight  study subjects tend to                                                                                                                                                                                                                                                                                                                                                              epidemiology. Some progress has already been made in 
                                                                           under-report their dietary intake9J0 and over-report their                                                                                                                                                                                                                                                                                                                                                            the development of questionnaires that assess longer- 
                                                                           activity”) and some reporting may be inaccurate simply                                                                                                                                                                                                                                                                                                                                                                term physical activity habits (to decrease the random er- 
                                                                           because respondents are not sufficiently aware of their                                                                                                                                                                                                                                                                                                                                                               ror attributable to daily changes in activity patterns), and 
                                                                           dietary intake to report it reliably. Substantial measure-                                                                                                                                                                                                                                                                                                                                                            that use cognitive methods to develop and administer the 
                                                                           ment error and consequent misclassification are known to                                                                                                                                                                                                                                                                                                                                                              questionnaire (to decrease random and systematic errors 
                                                                           exist in  nutritional epidemiologic studies, as do conse-                                                                                                                                                                                                                                                                                                                                                             attributable to recall errors and difficulties associated with 
                                                                           quent attenuation of the risk estimates and a reduction in                                                                                                                                                                                                                                                                                                                                                            estimation of past activity levels). One such example 
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        is 
                                                                           the probability of finding an existing diet-cancer relation-                                                                                                                                                                                                                                                                                                                                                          the Lifetime Total Physical Activity Questionnaire,2’ which 
                                                                           ship.12J3 Flegal14 has argued, however, that measurement                                                                                                                                                                                                                                                                                                                                                              was developed to measure all types of activity performed                                                                                                                                                                                                                                                                                                                                                                    Downloaded from https://academic.oup.com/nutritionreviews/article/59/11/349/1827811 by guest on 04 January 2023
                                                                           errors in dietary assessment are not always random and                                                                                                                                                                                                                                                                                                                                                                by respondents during their entire lifetimes. An additional 
                                                                           that it is erroneous to assume that random measurement                                                                                                                                                                                                                                                                                                                                                                improvement for physical activity questionnaires is to 
                                                                           error biases estimate only toward the null value.                                                                                                                                                                                                                                                                                                                                                                     avoid the use of grouped activities and to have respon- 
                                                                                                       Careful analysis of dietary data has revealed the diffi-                                                                                                                                                                                                                                                                                                                                  dents report the actual activities that they have performed 
                                                                           culties that respondents have when reporting their usual                                                                                                                                                                                                                                                                                                                                                              without the use of any predefined lists. Such an approach 
                                                                           dietary intake. These problems include omitting or incom-                                                                                                                                                                                                                                                                                                                                                             has been developed for interview-administered question- 
                                                                          pletely  specifying foods, reporting foods that are not                                                                                                                                                                                                                                                                                                                                                                naires; self-administered versions are under development.21 
                                                                           actually  consumed, or estimating portion sizes incor-                                                                                                                                                                                                                                                                                                                                                                This method is analogous to the interview-administered 
                                                                          rectly.I5-I7 Dietary assessment methods assume a certain                                                                                                                                                                                                                                                                                                                                                                diet history questionnaire in which respondents report all 
                                                                           level of knowledge about dietary constituents and the                                                                                                                                                                                                                                                                                                                                                                  foods that they normally consume either by meals during 
                                                                           ability to remember and estimate intake.18 New dietary as-                                                                                                                                                                                                                                                                                                                                                            the day or overall during the day. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA
                                                                          sessment methods are being developed that take into con- 
                                                                          sideration the cognitive processes that study subjects                                                                                                                                                                                                                                                                                                                                                                 Dietary and Lifestyle Patterns 
                                                                          undergo when responding to these types of questions.                                                                                                                                                                                                                                                                                                                                                                   The fourth methodological issue is the lack of consider- 
                                                                           Improvements in epidemiologic data collection methods                                                                                                                                                                                                                                                                                                                                                                  ation of patterns of exposure. Dietary assessment meth- 
                                                                          through the use of cognitive interviewing has been advo-                                                                                                                                                                                                                                                                                                                                                                ods to date have been restricted to capturing the intake of 
                                                                           cated by cognitive psychologists and survey research-                                                                                                                                                                                                                                                                                                                                                                  individual food items or groups of food items rather than 
                                                                           er~.~~ These methods have been used in the development                                                                                                                                                                                                                                                                                                                                                                 dietary patterns.  The main reason  for the focus on the 
                                                                           of dietary assessment methods (e.g., Dietary History Ques-                                                                                                                                                                                                                                                                                                                                                             assessment of individual foods rather than patterns of 
                                                                          tionnaire created by the                                                                                                                                                                                                                                                                                                                                                                                                intake in nutritional epidemiology relates to the feasibility 
                                                                                                                                                                                                                                   U.S. NC120), although much more 
                                                                          research in these methods is still needed. Assessments of                                                                                                                                                                                                                                                                                                                                                               and logistics of data collection methods. A few investiga- 
                                                                          dietary intake require that the respondents have adequate                                                                                                                                                                                                                                                                                                                                                               tors have attempted to analyze dietary patterns of intake 
                                                                          cognitive ability to estimate and quantify their intake and                                                                                                                                                                                                                                                                                                                                                             to identify dietary habits that are associated with increased 
                                                                          report the frequency and portion size of their regular di-                                                                                                                                                                                                                                                                                                                                                              or decreased risks of cancer or m~rtality.~~.~~ An “integra- 
                                                                           etary intake.                                                                                                                                                                                                                                                                                                                                                                                                          tive,” rather than a “decompositional,” approach to study- 
                                                                                                       Additional measurement errors arise when individual                                                                                                                                                                                                                                                                                                                                        ing the association between diet and cancer is receiving 
                                                                           foods are combined into one group in questionnaires zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBAmore recognition as a valid and more realistic method for 
                                                                                                                                                                                                                                                                                                                                                                                                                                              .I4 
                                                                           Respondents must then estimate how frequently they con-                                                                                                                                                                                                                                                                                                                                                                assessing the total impact of dietary habits on risk.24 The 
                                                                           sume a number of different foods and combine their esti-                                                                                                                                                                                                                                                                                                                                                               integrative approach emphasizes patterns and linkages of 
                                                                          mates to produce an overall intake value. Measurement                                                                                                                                                                                                                                                                                                                                                                   dietary lifestyle choices. Physical activity patterns over 
                                                                           errors result from the difficulty in estimating the overall                                                                                                                                                                                                                                                                                                                                                             lifetimes have only rarely been e~amined,2~3~~ but may be 
                                                                           frequency of the intake in addition to assigning the same                                                                                                                                                                                                                                                                                                                                                              more etiologically relevant than measures of single types 
                                                                          nutrient content to all foods within a food group. Hence,                                                                                                                                                                                                                                                                                                                                                                of activities performed for restricted time periods in life. A 
                                                                           in nutritional epidemiologic research, the recommended                                                                                                                                                                                                                                                                                                                                                                  clear need exists to broaden the definition  of physical 
                                                                           approach is to have respondents report individual foods,                                                                                                                                                                                                                                                                                                                                                                activity to examine entire lifetime activity patterns. 
                                                                           rather than grouped food items, wherever possible and to 
                                                                           develop and use nutrient databases that are more com-                                                                                                                                                                                                                                                                                                                                                                   Databases 
                                                                           plete and comprehensive.                                                                                                                                                                                                                                                                                                                                                                                                The fifth methodological issue in nutritional epidemiol- 
                                                                                                        The sources of random and systematic error found in                                                                                                                                                                                                                                                                                                                                        ogy is the lack of current, complete, and accurate informa- 
                                                                           nutritional epidemiologic studies are comparable with those                                                                                                                                                                                                                                                                                                                                                             tion on the composition of food products in the nutrient 
                                                                           that exist in physical activity studies. Improvements in                                                                                                                                                                                                                                                                                                                                                                databases used to estimate nutrient intake.27 These data- 
                                                                           physical activity assessment can be made by identifying                                                                                                                                                                                                                                                                                                                                                                 bases are subject to changes in nutrient content of foods zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA
                                                                           352 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      Nutrition Reviews@, Vol. 59, No. 11 
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...November zyxwvutsrqponmlkjihgfedcbazyxwvutsrqponmlkjihgfedcba lead review article physical activity and cancer lessons learned from nutritional epidemiology christine m friedenreich ph d downloaded https academic oup com nutritionreviews by guest on january state of scientific evidence for convincing epidemiologic currently ex in etiology ists an association between the prevention colon breast a comprehensive literature may also reduce risk can was recently cer at several other sites with increasing research conducted that used classifications sci this topic it is apparent studies entific had been developed panel have numerous methodologi scientists who wrote report world re cal similarities nutrition...

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