CAMBRIDGE, Mass., Sep 21, 2001 (United Press International via COMTEX) -- Too much dietary calcium, like that found in dairy products, can increase the risk of developing prostate cancer, Harvard researchers report.

"This is a 'head's up' rather than the sounding of an alarm," said lead author Dr. June Chan, formerly a researcher at Harvard University Medical School in Cambridge and now assistant professor of epidemiology and urology at the University of California, San Francisco.

"Awareness of prostate cancer as a public health issue is growing in our culture. It's something that people are beginning to talk about and it is important to talk about it," Chan told United Press International. "Our study extends the discussion to the area of diet. This matters since diet is a moderate risk factor for the condition."

For 11 years, the Physicians' Health Study at Harvard gathered health, dietary and lifestyle data from 20,885 male physicians. Of these men, 1,012 developed prostate cancer. Chan and her associates examined data on each man and correlated calcium intake to incidence of prostate cancer. The investigators created a daily dairy score for each subject, adding up the calcium intake of five common dairy foods: whole milk, skim milk, cold breakfast cereal, cheese and ice cream. They found the highest 20 percent of dairy product consumers had a 34 percent greater risk of prostate cancer.

"To put this in perspective, saturated fat from red meat intake has been associated with a 200 to 250 percent increase risk of certain cancers. So what we are talking about here is a relatively modest increase in risk, but one that men should be aware of," Chan said.

The researchers said dietary calcium increases prostate cancer risk by suppressing the production of 1,25-dihydroxyvitamin D3, the most active form of vitamin D. Other research has identified this form of vitamin D as an inhibitor of prostate cancer cell growth. They found men who drank more than six glasses of milk a week had lower levels of this form of vitamin D than men who drank fewer than two glasses a week.

"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," the authors wrote.

"However, I realize that there are trade offs and that people have to consider other conditions, like the risk of colon cancer and osteoporosis, when they make their choices about calcium intake," Chan said. "There is a growing body of evidence that agrees with our conclusions in this study. But things have to be kept in balance, especially if there is a family history of particular medical conditions developing with age that might require use of certain diets or supplements."

"The men in this study at increased risk were those getting far more than 1,500 milligrams of calcium in their diets. Men who are keeping their intake to the recommended levels are not at increased risk," said Dr. David Heber, author of "What Color Is Your Diet? The Seven Colors Of Health" and chief of the division of clinical nutrition in the Department of Medicine at the University of California, Los Angeles. "And the really important thing in preventive care for the prostate is getting a lot of vegetables and fruits in the diet."

The National Institutes of Health recommend men younger than 65 years old get 1,000 mg of calcium a day from diet and supplements. Men over 65 should get 1,500 mg per day. The NIH also recommend daily calcium intake not exceed 2,000 mg. The government has noted about half of the American population is estimated to consume less than 600 mg of calcium daily, which has been determined to be inadequate for good health.

Reported by Bruce Sylvester from West Palm Beach, Fla.