Dairy products, calcium, and prostate cancer risk in the Physicians' Health Study.

BACKGROUND A high calcium intake, mainly from dairy products, may increase prostate cancer risk by lowering concentrations of 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)], a hormone thought to protect against prostate cancer. The results of epidemiologic studies of this hypothesis are inconclusive. OBJECTIVE We investigated the association between dairy product and calcium intakes and prostate cancer risk in the Physicians' Health Study, a cohort of male US physicians. DESIGN At baseline, the men answered abbreviated dietary questionnaires. During 11 y of follow-up, we documented 1012 incident cases of prostate cancer among 20885 men. We estimated dairy calcium intake on the basis of consumption of 5 major dairy products and used logistic regression to estimate relative risk. RESULTS At baseline, men who consumed >600 mg Ca/d from skim milk had lower plasma 1,25(OH)(2)D(3) concentrations than did those consuming < or =150 mg Ca/d [71 compared with 85 pmol/L (30.06 compared with 35.64 pg/mL); P = 0.005]. Compared with men consuming < or =0.5 daily servings of dairy products, those consuming >2.5 servings had a multivariate relative risk of prostate cancer of 1.34 (95% CI: 1.04, 1.71) after adjustment for baseline age, body mass index, smoking, exercise, and randomized treatment assignment in the original placebo-controlled trial. Compared with men consuming < or =150 mg Ca/d from dairy products, men consuming >600 mg/d had a 32% higher risk of prostate cancer (95% CI: 1.08, 1.63). CONCLUSIONS These results support the hypothesis that dairy products and calcium are associated with a greater risk of prostate cancer.