Extra vitamin D and calcium may offer some protection against fractures in elderly people, but has little or no impact on cancer risk, according to review of the medical evidence.
Some research has suggested that vitamin D, with or without calcium, might help reduce cancer risk, but recent trials have dashed those hopes.
The new report, out this week in the Annals of Internal Medicine, was commissioned by the government-backed U.S. Preventive Services Task Force to inform its public recommendations.
It pulls together 19 randomized controlled trials on vitamin D with or without calcium. The trials lasted anywhere from seven months to seven years and ranged in size from a few thousand participants to tens of thousands.
Only three of them reported on cancer, however. While one small study found some protection against cancer in postmenopausal women taking vitamin D and calcium, the larger studies found no benefits.
The American Cancer Society does not advise dietary supplements to prevent cancer. There is no compelling evidence currently that taking supplements will lower your cancer risk.
The Institute of Medicine recommends that most adults get 1,000 to 1,200 milligrams (mg) of calcium per day and 600 to 800 IU of vitamin D. It sets a recommended upper limit at 2,000 mg of calcium and 4,000 IU of vitamin D.
The research team did find a small reduction in fracture risk among elderly people living in an institution such as a nursing home, with extra vitamin D and calcium preventing two out of every 100 expected fractures.
But the risk reduction was smaller for people living on their own, and might have been due to chance.
The researcher said that in an earlier report from 2009, which looked at several possible health benefits, only the fracture benefit was convincing.
It is possible that people who have low levels of vitamin D may get some benefit, but that doesn't warrant everybody taking extra vitamins.
The U.S. Preventive Services Task Force did not say when its new vitamin D guidelines will be released.
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