Milk - Prostate Cancer Link?

24 September 2001
Milk - Prostate Cancer Link?
by George Atkinson

According to a new study in the American Journal of Clinical Nutrition, the risk of prostate cancer in men may increase with calcium intake, especially from dairy products. As part of the Physicians' Health Study, Chan et al. investigated the connection between dairy product and calcium consumption and prostate cancer in a large group of male U.S. physicians. Compared with the men who consumed less than .5 serving of dairy products daily, men who consumed more than 2.5 servings had a 34% higher risk of developing prostate cancer. The study group of 20,885 male physicians completed self-administered questionnaires concerning diet and lifestyle between 1982 and 1995. During 11 years of follow-up, 1012 incidents of prostate cancer were reported. The investigators created a dairy score for each participant by summing up the daily calcium contributions from each of 5 common dairy foods.

Men in the highest quintiles of dairy product consumption had a significant 34% greater risk of prostate cancer when compared to those in the lowest categories. When calcium intake was examined apart from dairy product consumption, the risk ratio was 30% higher for advanced prostate cancer and 47% higher for nonadvanced cases. Of the dairy products consumed by the participants, only skim milk was individually positively associated with prostate cancer risk, perhaps because it accounted for 48% of total consumption of dairy foods.

The authors propose that dietary calcium increases prostate cancer risk by suppressing the production of 1,25-dihydroxyvitamin D3, the most active form of vitamin D, which is thought to protect against this disease. Examination of vitamin D metabolites in a subset of the study population revealed that those with the highest quintile of calcium consumption (>600 mg/day) had 17% lower serum concentrations of 1,25-dihydroxyvitamin D3 than those in the lowest quintile of calcium consumption ( ' 150 mg/day). Although the study did not address supplemental calcium consumption, previous studies limited to supplements have demonstrated similar risk ratios.

The authors conclude that, "These findings may serve to interject a note of caution into the current enthusiastic promotion of a higher intake of calcium in the United States."