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."
Chan, June M, et al. Dairy products, calcium and prostate cancer risk in the Physicians' Health Study. Am J Clin Nutr 2001;74:549-54.
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