Dairy foods, calcium and prostate cancer risk - Vitamins and Minerals - Brief Article

Nutrition Research Newsletter, Nov, 2001

Prostate cancer is the most common cancer among men in the United States and is a leading cause of cancer death. Recently, several dietary risk factors have been investigated regarding their link to prostrate cancer. Some studies have shown that greater intakes of dairy products, meat, fat and total energy and lower intakes of tomato products, selenium, lycopene and vitamin E have all been linked to higher prostate cancer risk.

Countries with higher consumption of dairy products have a higher incidence of prostate cancer than do countries in which few dairy products are consumed. Although it is not confirmed, the authors suggest that dietary calcium (found in dairy products) could influence prostate cancer development by down regulating the production of 1,25-dihydroxyvitamin [D.sub.3], a hormone thought to protect against this cancer. Since the results of epidemiological studies of this and other hypotheses on this topic are inconclusive, an article in the American Journal of Clinical Nutrition investigated the association between dairy products, calcium intake and prostate cancer risk in the Physicians' Health Study.

The Physicians' Health Study was a randomized trial of aspirin and beta-carotene among 22,071 US male physicians. During follow-up for data for this study, 1,012 self-reported cases of prostate cancer were found. These men then completed questionnaires that assessed dietary and other lifestyle habits. At 18 weeks and 24 months, the men reported their consumption of cold breakfast cereal, whole milk and skim milk: at 12 months, they reported intakes of cheese and ice cream. Chan et al. estimated dairy calcium intake on the basis of consumption of these five diary products and used logistic regression to estimate relative risk.

Men who consumed the most servings of dairy products per day were apt to smoke less, exercise more frequently, be older and were more likely current users of multivitamins than were men who consumed the least servings of dairy products. Skim milk was the major contributor to dairy product intake. accounting for 57 percent of the total assessed dairy calcium intake. Men in the highest categories of dairy product and calcium intakes had a statistically significant (~30 percent) greater risk of prostate cancer than did those in the lowest consumption categories. Each additional 500-mg of calcium from dairy products consumed per day coincided with a 16 percent increase in prostate cancer risk. At the baseline, men who consumed more than 600 mg calcium per day from skim milk had lower plasma 1.25[(OH).sub.2][D.sub.3] concentrations than did those consuming 150 mg or less of calcium per day.

These results are in agreement with previous studies that suggest that calcium and dairy foods are associated with a greater risk of prostate cancer. The authors acknowledge some limitations to the study but are quick to defend them. Chan et al. recognize the possibility that some other component of dairy foods (for example, dairy fat) and not calcium could account for the observed associations. However, skim milk was the dairy food most strongly related to risk and dairy fat and dairy protein were not significantly associated with risk. Also, supplement usage was not considered in this study. Additional investigations of this hypothesis, including a more comprehensive assessment of diet and supplement use, are appropriate.

James M. Chan, Meir J. Stampfer, Jing Ma, Peter H. Gann, et al. Dairy products, calcium, and prostate cancer risk in the Physicians' Health Study. American Journal of Clinical Nutrition 74: 549-554 (October 2001) [Address reprint requests to: J.M. Chan, Departments of Epidemiology and Biostatistics & Urology, University of California, San Francisco, 3333 California Street, Suite 280, San Francisco, CA 94143-1228. E-mail: june.chan@channing.harvard.edu.]