© 2001 by Oxford University Press
Journal of the National Cancer Institute, Vol. 93, No. 10, 791,
May 16, 2001
© 2001 Oxford University Press
CORRESPONDENCE |
Response
Affiliations of authors: K. B. Michels, Channing Laboratory, Department of Medicine, Brigham and Women's Hospital, and Harvard Medical School, and Department of Epidemiology, Harvard School of Public Health, Boston, MA; E. Giovannucci, Channing Laboratory, Department of Medicine, Brigham and Women's Hospital, and Departments of Nutrition and Epidemiology, Harvard School of Public Health; D. Feskanich, Channing Laboratory, Department of Medicine, Brigham and Women's Hospital, and Harvard Medical School; W. C. Willett, Departments of Nutrition and Epidemiology, Harvard School of Public Health, and Channing Laboratory, Department of Medicine, Brigham and Women's Hospital, and Harvard Medical School.
Correspondence to: Karin B. Michels, Sc.D., Channing Laboratory, 181 Longwood Ave., Boston, MA 02115 (e-mail: kmichels{at}rics.bwh.harvard.edu).
We thank Drs. Nelson, Persky, and Turyk for emphasizing that colorectal cancer is largely preventable. Indeed, we agree that much progress has been made in recent years to identify modifiable factors that can prevent colon cancer: increasing physical activity, avoiding obesity, using folic acid-containing multivitamin supplements, not smoking, reducing alcohol use, and reducing red meat consumption. We raised these issues in our recent article in the Journal (1) and have estimated that more than 70% of colon cancer cases might be preventable by modification of the diet and lifestyle risk factors (2).
Studies with migrant populations indicate that environmental factors play a role in colorectal carcinogenesis, but factors other than diet—listed above—may also contribute. Recent data suggest that some aspects of diet may not be as important as previously assumed. While consumption of red meat has frequently emerged across studies as a risk factor for colorectal cancer and folic acid seems to reduce the risk, dietary fiber (3,4) and consumption of fruit and vegetables (1,5,6) seem less influential. This lack of an association is fairly consistent among more recent prospective cohort studies, in which problems of recall and selection bias are avoided. Also, large cohort studies have accounted for numerous potentially confounding variables. Nelson et al. mention a trend of increasing fiber consumption captured by the National Health and Nutrition Examination Survey that coincides in time with a decrease in colorectal cancer incidence. However, many variables have changed over time so that time trends may not reflect causal relations. For example, in the mid-1970s, the U.S. Food and Drug Administration first allowed the recommended dietary allowance level of folic acid to be added to multiple vitamins; in contrast to fiber, a beneficial effect of folic acid has been supported in epidemiologic studies [e.g., (7)].
We agree with Nelson et al. that screening and polypectomy can play a role in colorectal cancer prevention, but it is even more important to act on other modifiable risk factors that can prevent the large majority of cases and that will have many other health benefits as well.
REFERENCES
1
Michels KB, Giovannucci E, Joshipura KJ, Rosner BA, Stampfer MJ, Fuchs CS, et al. Prospective study of fruit and vegetable consumption and incidence of colon and rectal cancers. J Natl Cancer Inst 2000;92:1740–52.
2 Platz EA, Willett WC, Colditz GA, Rimm EB, Spiegelman D, Giovannucci E. Proportion of colon cancer risk that might be preventable in a cohort of middle-aged US men. Cancer Causes Control 2000;11:579–88.[CrossRef][ISI][Medline]cancerlit;20431614
3
Fuchs CS, Giovannucci EL, Colditz GA, Hunter DJ, Stampfer MJ, Rosner B, et al. Dietary fiber and the risk of colorectal cancer and adenoma in women. N Engl J Med 1999;340:169–76.
4
Schatzkin A, Lanza E, Corle D, Lance P, Iber F, Caan B, et al. Lack of effect of a low-fat, high-fiber diet on the recurrence of colorectal adenomas. Polyp Prevention Trial Study Group. N Engl J Med 2000;342:1149–55.
5
Steinmetz KA, Kushi LH, Bostick RM, Folsom AR, Potter JD. Vegetables, fruit, and colon cancer in the Iowa Women's Health Study. Am J Epidemiol 1994;139:1–15.
6
Voorrips LE, Goldbohm RA, van Poppel G, Sturmans F, Hermus RJ, van den Brandt PA. Vegetable and fruit consumption and risks of colon and rectal cancer in a prospective cohort study. The Netherlands Cohort Study on Diet and Cancer. Am J Epidemiol 2000;152:1081–92.
7
Giovannucci E, Stampfer MJ, Colditz GA, Hunter DJ, Fuchs C, Rosner BA, et al. Multivitamin use, folate, and colon cancer in women in the Nurses' Health Study. Ann Intern Med 1998;129:517–24.
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