Monday Dec 22 2008 (foodconsumer.org) - Eating dairy products often may be a risk factor for prostate cancer, a study published in American Journal of Clinical Nutrition suggests.

The study led by Edward L Giovannucci and colleagues at Harvard Medical School showed that men who consumed more than 2.5 servings of dairy products daily were 34 percent more likely to be diagnosed with prostate cancer than those who consumed less than 0.5 servings.

The study involved 20,885 men who participated in the Physicians' Health Study, a cohort of male US physicians and during an 11-year follow-up, 1,012 incident cases of prostate cancer were identified.

For the study, the researchers estimated dairy calcium intake on the basis of consumption of 5 dairy products namely cold breakfast cereal, whole milk, and skim milk, cheese and ice cream and associated intake of calcium and dairy products with the risk of prostate cancer. These 5 dairy products were the main sources of dietary calcium for the study population.

The researchers found each additional 500 mg of calcium from dairy products per day was associated with a 16 percent increase in the risk of prostate cancer. The association was similar even intake of other foods such as chicken, fish, and eggs was considered.

When the 5 dairy foods were considered individually, the researchers found only skim milk was significantly positively related to prostate cancer and men who consumed one or more servings per day were 32 percent more likely to have prostate cancer than those who did not consume any dairy products.

Skim milk accounted for 48 percent of total dairy product intake and 57 percent of the total dairy calcium intake.

The association between intake of dairy products and risk of prostate cancer was apparently due not to the dairy fat which was not correlated with the risk although dairy protein was linked with the risk.   Those who were in the quintile of highest dairy protein intake were at a 21 percent risk for developing prostate cancer than those who had the lowest quintile of intake.

Men who had the highest intake of dairy products were 38 and 42 percent more likely to have advanced and non- advanced prostate cancer respectively than those who had the lowest intake.   Similarly men who had the highest intake of calcium from dairy products were 30 and 47 percent more likely to be diagnosed with advanced and nonadvanced prostate cancer respectively than those who had the lowest intake.

Giovannucci and colleagues speculated that calcium is the key element that mediated that association between intake of dairy products and prostate cancer risk.   In fact they found the association of calcium intake from dairy products with prostate cancer risk was virtually the same as the one of dairy products, that is, those who had greater than 600 mg calcium per day were 32 percent more likely to develop prostate cancer than those who had only less than 150 mg per day.

The researchers proposed that the effect of calcium on the prostate cancer is mediated by its effect on the production of 1, 25-dihydroxyvitamin D3, the most potent form of vitamin D in the body that has been found to protect against more than at least 17 types of cancer at high serum concentrations. They proposed that high intake of calcium suppressed the production of 1, 25-dihydorxyvitamin D3, raising the prostate cancer risk.

They found that after adjustment for age, body mass index, and smoking status, dairy calcium intake was significantly inverse associated with 1, 25-dihydroxyvitamin D3 concentrations. Each 300-mg increase in total daily intake from dairy products, 1, 25-dihydroxyvitamin D3 declined 2 pmol/L or 1.02 pg/mL.

Men who consumed more than 600 mg calcium per day from skim milk had a lower 1,25-dihydroxyvitamin D3 level than those who had less than 150 mg calcium from skim milk, 71 pmol/L (30.06 pg/mL) versus 85 pmol/L (35.64 pg/mL).

Calcium from skim milk was also significantly inversely associated with serum concentrations of 1, 25-dihdyroxyvitamin D3.   But skim milk calcium was not correlated with serum concentration of 25(OH)D, which the researchers said was understandable because most 25(OH)D is derived from sun exposure.

The researchers said in their report that twelve of 14 epidemiologic studies previously showed that highest intake of dairy products was associated with a 1.5 to 2.5 times higher risk of prostate cancer compared to those who had the lowest intake.

At least two studies, according to the authors, have suggested that dietary calcium could affect prostate cancer risk by down-regulating the production of 1, 25-dihydroxyvitamin D3, a hormone believed to protect against prostate cancer.

The researchers suggested that it is less likely that serum calcium has a direct impact on the risk of prostate cancer because the serum concentration of calcium is tightly regulated. But at least one study, according to the authors, showed that physiologic concentrations of dietary calcium can suppress the production of circulating 1, 25-dihydroxyvitamin D3 by down-regulating parathyroid hormone, leading to a high risk of prostate cancer.

"In conclusion, this report supports and extends previous observations that high intakes of dairy products, and of calcium from dairy foods specifically, are associated with an increased risk of prostate cancer," the researchers wrote.