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A new study published in the July issue of the journal The Oncologist has suggested that calcium and vitamin D supplements prescribed for men at risk of bone loss from hormonal treatment for prostate cancer may increase the risk of cardiovascular disease and aggressive prostate cancer.

"Calcium and/or vitamin D supplementation to prevent loss of bone mineral density in these men seems so logical that no one had questioned whether it works," Mridul Datta, co-author of the study, said.  "We used these data to determine whether calcium and vitamin D supplements prevented bone loss in these men," Datta said. "The answer clearly is, 'No.'"

Researchers said that the presumption of benefit from calcium and vitamin D supplements that have been routinely recommended to these men must be rigorously evaluated.

Epidemiologists from the Wake Forest Baptist Medical Center reviewed guidelines for calcium and/or vitamin D supplementation. They also reviewed the results of 12 clinical trials of supplemental calcium and/or vitamin D in a total of 2,399 men with prostate cancer undergoing androgen deprivation therapy (ADT), as well as the measurements of bone mineral density before and after ADT.

ADT is the mainstay treatment for men with advanced prostate cancer. It reduces serum levels of androgens on which most prostate cancers depend. Like women undergoing menopause, a side effect of ADT in men is bone loss, or osteoporosis. Consequently, many physicians recommend calcium and vitamin D supplements to help reduce fracture risk in these men, which can be a significant problem. 

One in 10 of these men will experience a fracture within two years of therapy.

The study showed that even taking the recommended dose of 500 to 1,000 mg of calcium and 200 to 500 IU of vitamin D per day, men undergoing ADT lost bone mineral density.

Researchers said the lack of an obvious benefit is worrisome because other data show an association between increased dietary calcium and an increased risk of aggressive prostate cancer and heart disease. 

They also said more research is needed to verify these findings by comparing a calcium and vitamin D supplement treated group vs. a non-supplemented group and looking not only at the potential benefits - in bone mineral density and in the risk of fracture -- but also at the possible risks, including unwanted cardiovascular effects and the effects on prostate cancer itself.