Many Americans have been warned that they’re deficient in vitamin D and need to take supplements to protect against all the purported ills of getting too little of the vitamin, such as heart disease, diabetes, fractures, and a variety of cancers. Yet the latest review of research, conducted by a Tufts Medical Center team, suggests that many of the supposed benefits of supplementation remain unproven and that taking too high a dose of D -- a fat-soluble vitamin that has hormone-like effects -- can increase the risk of problems it’s supposed to prevent.
The review, published Monday in the Annals of Internal Medicine, examined 19 clinical trials comparing supplements with placebos and found that fractures could be reduced in those who took calcium along with vitamin D but that the biggest benefits were conferred on elderly folks confined to nursing homes or hospitals. The data were mixed on cancer prevention. Some studies showed that taking 1,000 international units a day of vitamin D could reduce the risk of cancer, while others showed no benefit or an increased risk.