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)2D3 concentrations than did those consuming less than or equal 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 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 less than or equal to 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.