Prospective Study of Fruit and Vegetable Consumption and Incidence of Colon and Rectal Cancers Karin B. Michels, Edward Giovannucci, Kaumudi J. Joshipura, Bernard A. Rosner, Meir J. Stampfer, Charles S. Fuchs, Graham A. Colditz, Frank E. Speizer, Walter C. Willett Affiliations of authors: K. B. Michels, M. J. Stampfer, Channing Laboratory, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, and Department of Epidemiology, Harvard School of Public Health, Boston; E. Giovannucci, Channing Laboratory, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, and Department of Nutrition, Harvard School of Public Health, Boston; K. J. Joshipura, Department of Epidemiology, Harvard School of Public Health, and Department of Oral Health Policy and Epidemiology, Harvard School of Dental Medicine, Boston; B. A. Rosner, Channing Laboratory, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, and Department of Biostatistics, Harvard School of Public Health; C. S. Fuchs, Channing Laboratory, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, and Department of Adult Oncology, Dana-Farber Cancer Institute, Boston; G. A. Colditz, Channing Laboratory, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, and Department of Epidemiology and Harvard Center for Cancer Prevention, Harvard School of Public Health; F. E. Speizer, Channing Laboratory, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School; W. C. Willett, Channing Laboratory, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, and Departments of Epidemiology and Nutrition, Harvard School of Public Health. Correspondence to: Karin B. Michels, Sc.D., Channing Laboratory, 181 Longwood Ave., Boston, MA 02115 (e-mail: kmichels@rics.bwh.harvard.edu). Background: Frequent consumption of fruit and vegetables has been associated with a reduced risk of colorectal cancer in many observational studies. Methods: We prospectively investigated the association between fruit and vegetable consumption and the incidence of colon and rectal cancers in two large cohorts: the Nurses' Health Study (88 764 women) and the Health Professionals' Follow-up Study (47 325 men). Diet was assessed and cumulatively updated in 1980, 1984, 1986, and 1990 among women and in 1986 and 1990 among men. The incidence of cancer of the colon and rectum was ascertained up to June or January of 1996, respectively. Relative risk (RR) estimates were calculated with the use of pooled logistic regression models accounting for various potential confounders. All statistical tests were two-sided. Results: With a follow-up including 1 743 645 person-years and 937 cases of colon cancer, we found little association of colon cancer incidence with fruit and vegetable consumption. For women and men combined, a difference in fruit and vegetable consumption of one additional serving per day was associated with a covariate-adjusted RR of 1.02 (95% confidence interval [CI] = 0.98–1.05). A difference in vegetable consumption of one additional serving per day was associated with an RR of 1.03 (95% CI = 0.97–1.09). Similar results were obtained for women and men considered separately. A difference in fruit consumption of one additional serving per day was associated with a covariate-adjusted RR for colon cancer of 0.96 (95% CI = 0.89–1.03) among women and 1.08 (95% CI = 1.00–1.16) among men. For rectal cancer (total, 244 cases), a difference in fruit and vegetable consumption of one additional serving per day was associated with an RR of 1.02 (95% CI = 0.95–1.09) in men and women combined. None of these associations was modified by vitamin supplement use or smoking habits. Conclusions: Although fruits and vegetables may confer protection against some chronic diseases, their frequent consumption does not appear to confer protection from colon or rectal cancer. SEE BELOW FOR AN ANSWER FROM Am Insitute for Cancer Research - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Cancer Researchers to Harvard Nurses Study: Not So Fast! Link between Fruit, Vegetable Consumption and Lowered Risk for Colon Cancer Remains Clear, Convincing WASHINGTON, Oct. 31 (American Institute for Cancer Research) — The American Institute for Cancer Research (AICR) today cautioned the public not to abandon diets that have been shown to protect against cancer merely because a recent study failed to find a protective effect. The Institute reminded the public of the "convincing and continually growing" scientific evidence that diets high in fruits and vegetables lower the risk for colon cancer. AICR was responding to the latest findings of Harvard's Nurses Health Study and the Health Professionals Follow-up Study, published in the Nov. 1 issue of the Journal of the National Cancer Institute. The surveys of 136,092 men and women reported no link between consumption of fruits and vegetables and colon cancer risk. "The public needs to keep in mind that this finding contradicts the bulk of available evidence on the link between high consumption of fruits and vegetables and lower risks of cancer," said John Potter, M.D., Ph.D., head of the Cancer Prevention Research Program at Seattle's Fred Hutchinson Cancer Research Center. People may be misled by the tremendous amount of publicity this particular ongoing study often receives, he said. He stressed the need to keep these new results in a larger context. "The data show that the subjects in these studies were consuming very few fruits and vegetables," said Ritva Butrum, Ph.D., vice president for research at AICR. "Five to nine servings a day are recommended for protection against cancer, but most of the respondees consumed far less. In fact, fewer than 2 percent of those in the Nurses' cohort reported eating more than four servings of vegetables a day, while only 3 percent of those in the Health Professionals' cohort said they consumed more than three servings of vegetables a day. "This indicates that the studies' variability -- in this case, the statistical range between those respondees who consume the most and the least amount of fruits and vegetables -- is small. Statistically speaking, when variability is low, the association with high or low consumption gets harder to see," Butrum said. Dr. Potter noted an additional consideration. "A greater issue is whether the analysis should actually control for total energy intake," he said. "Table 1 of the report makes it clear that those who consumed more fruits and vegetables consumed more food in general. A greater calorie consumption may have blunted the association one would expect to see with fruits and vegetables alone." For these and other reasons related to their methodology, Dr. Potter said, the Nurses Study and Health Professionals Study do not and cannot make a definitive determination about the presence or absence of a protective effect. "It would be a mistake to interpret these results as anything but what they are: a single set of findings on an important topic that's attracting more and more scientific attention each day." Study's Limitations Noted Because the Nurses and Health Professionals study is held to be the "gold standard" of nutrition research by some members of the media, the public is largely unaware of the important limitations in the study's design. Cancer experts agree that no single study can prove or disprove any association. This is because each kind of study is specifically designed to examine very specific aspects of the diet-cancer connection. Dependable scientific consensus only emerges once different studies of different design performed by different investigators have been examined. The Nurses and Health Professionals study, for example, is a cohort study. It tracks subjects by asking them to fill out a biennial questionnaire about their diet and lifestyle. No control group exists, and the limitations of self-reporting as a means of assessment is a hotly debated scientific topic. "It is vital not to start over-interpreting recent studies merely because they are recent," said Dr. Potter. "We should wait and see how these data compare to the considerable body of research that is mounting across the globe," Dr. Potter said. "The Nurses Study should contribute to ongoing scientific discourse," he added, "not replace it." Dr. Potter is a professor of epidemiology at the University of Washington and recognized as a global leader in his field. He has published extensively on the causes of colorectal cancer, the role of plant foods in lowering cancer risk, and the interaction of environmental and genetic factors in determining cancer risk. He is Senior Editor for the scientific journal, Cancer, Epidemiology, Biomarkers and Prevention. The American Institute for Cancer Research is the only major cancer charity focusing exclusively on the link between diet and cancer. The Institute provides a wide range of consumer education programs that have helped millions of Americans learn to make changes for lower cancer risk. AICR also supports innovative research in cancer prevention and treatment at universities, hospitals and research centers across the U.S. The Institute has provided over $50 million in funding for research in diet, nutrition and cancer. 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