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 calciu m intakes and prostate cancer risk in the Physicians' Health Study, a cohor t of male US physicians. Design: At baseline, the men answered abbreviated dietary questionnaires. D uring 11 y of follow-up, we documented 1012 incident cases of prostate canc er among 20885 men. We estimated dairy calcium intake on the basis of consu mption of 5 major dairy products and used logistic regression to estimate r elative risk. Results: At baseline, men who consumed >600 mg Ca/d from skim milk had lowe r plasma 1,25(OH)2D3 concentrations than did those consuming less than or e qual to 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 less than or equal to0.5 dail y servings of dairy products, those consuming >2.5 servings had a multivari ate relative risk of prostate cancer of 1.34 (95% CI: 1.04, 1.71) after adj ustment for baseline age, body mass index, smoking, exercise, and randomize d treatment assignment in the original placebo-controlled trial. Compared w ith men consuming less than or equal to 150 mg Ca/d from dairy products, me n consuming >600 mg/d had a 32% higher risk of prostate cancer (95% CI: 1.0 8, 1.63). Conclusions: These results support the hypothesis that dairy products and c alcium are associated with a greater risk of prostate cancer.