The study by Wake Forest Baptist Medical Center researchers showed that the calcium doses commonly recommended to prostate cancer patients, made their bones thinner and also increased the risk of heart disease, the 'Daily Mail' reported.
"The wakeup call of these findings is that the presumption of benefit from calcium and vitamin D supplements that have been routinely recommended to these men must be rigorously evaluated," researcher Mridul Datta was quoted as saying by the paper.
A review of trial data concluded the supplements do not improve bone strength and may increase the risk of heart disease and more aggressive cancer.
At least 5,000 men with prostate cancer are given hormonal therapy each year in the UK. It works by blocking the production of male hormones, but it also makes fractures more likely.
"We used these data to determine whether calcium and vitamin D supplements prevented bone loss in these men. The answer clearly is, "No"," Datta said.
Researchers reviewed guidelines for calcium and vitamin D supplementation, taking measurements of bone density before and after the men were prescribed hormonal therapy.
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The study shows a link between between increased dietary calcium and a greater risk of aggressive prostate cancer and heart disease.
The Food Standards Agency recommends adults have 700mg of calcium a day, which should come from dietary sources including milk, cheese and green, leafy vegetables.
The findings were published in the journal 'The Oncologist'.