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More Support For Link Between Calcium And Prostate Cancer Risk

Data from the United States Physicians? Health Study offers more support for the association between high intake of calcium from dairy products and a greater risk of prostate cancer.

During 11 years of follow-up, North American researchers documented 1,012 incident cases of prostate cancer among 20,885 doctors in the study.

"Compared with men consuming 150 milligrams or less of calcium per day from dairy products, men consuming more than 600 mg/d had a 32 percent higher risk of prostate cancer," they report.

Investigators say their results support and extend previous observations that high intakes of dairy products, and of calcium from dairy foods specifically, are associated with an increased risk of prostate cancer.

"These findings may serve to interject a note of caution into the current enthusiastic promotion of a higher intake of calcium in the US," they add.

They explain that a high calcium intake, mainly from dairy products, could increase prostate cancer risk by lowering concentrations of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3]. They add that 1,25(OH)2D3 is a hormone believed to help protect against prostate cancer.

Participants in the overall Physicians' Health Study completed questionnaires at start-up in 1982. They reported annually through 1995 in a randomised, blinded, placebo-controlled trial that looked at their aspirin and beta-carotene use.

In this study, researchers from Harvard University, Brigham and Women?s Hospital and the Veterans Administration Boston Health Care System, all in Boston, Massachusetts, and Northwestern University in Chicago, Illinois used data from participants who returned dietary questionnaires, provided body mass index statistics and did not have a cancer diagnosis at baseline.

Their follow-up was more than 99 percent complete.

Investigators estimated dairy calcium intake using consumption of five major dairy products. They used logistic regression to estimate relative risk.

"At baseline, men who consumed more than 600 mg Ca/d from skim milk had lower plasma 1,25(OH)2D3 concentrations than did those consuming 150 mg Ca/d or less," they say.

"Compared with men consuming 0.5 daily servings of dairy products or less, those consuming more than 2.5 servings had a multivariate relative risk of prostate cancer of 1.34, after adjustment for baseline age, [body mass index], smoking, exercise and randomised treatment assignment in the original placebo-controlled trial."

Researchers note that the positive associations for dairy products and dairy calcium especially remained after they adjusted for total food scores.

"Thus, our inability to control for total energy probably introduced little or no bias, and random classification of the main exposure as a result of incomplete dairy calcium assessment would lead to an underestimate of any true associations," they conclude.
American Journal of Clinical Nutrition, 2001; 74: 549-554

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