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Vitamin D Supplements: FAQ

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WebMD Health News

Vitamins spilling from bottle

Feb. 3, 2014 -- Vitamin D had been gaining a reputation as a ''wonder supplement." Studies have suggested it can help bone and heart health, ease mild depression, and lower the risk of cancer. Others have suggested it might help people with fibromyalgia, multiple sclerosis, and other chronic diseases.

Now comes a different finding. Researchers who looked at dozens of studies say that vitamin D supplements do not lower the risks of heart attacks, strokes, cancer, or fractures by more than 15% in generally healthy people. This was true whether or not the supplements included calcium.

Bottom line: For most healthy adults, vitamin D supplements are not worth it, the researchers say in The Lancet Diabetes & Endocrinology.

Not everyone agrees, and the debate is far from done. Here, two experts address the most common questions about vitamin D supplements.

Are vitamin D supplements losing their luster?

"I believe so," says Doug Campos-Outcalt, MD, of the University of Arizona College of Medicine, Phoenix. He recently wrote a review of vitamin D for The Journal of Family Practice.

Evidence shows that vitamin D helps bone health, he says. But early studies that show vitamin D may help in other areas, such as heart health and cancer prevention, are not convincing. 

"Information on the health benefits of vitamin D is difficult to sort out," he writes in the review. He cites a report from the Institute of Medicine, an independent organization that provides health advice. The institute looked at studies of vitamin D to protect against cancer, heart disease, diabetes, and autoimmune diseases such as lupus. Except for bone health, it found no evidence that vitamin D helped with any other diseases.

Robert R. Recker, MD, director of osteoporosis research at Creighton University School of Medicine in Nebraska, disagrees. He cites research finding vitamin D lowers the risks of colon, breast, and other cancers, and improves how the immune system works.

On the other hand, other experts say low vitamin D levels may be a result of illness, not the cause.

What do we know for sure about vitamin D?

What it does: Experts agree on the basics. Vitamin D helps the body absorb calcium, and that is good for bone health. Vitamin D also helps reduce inflammation in our cells. Inflammation can trigger disease.

What are the main areas of disagreement about Vitamin D?

How much is needed: At the center of the debate is how much vitamin D is enough. "We need more vitamin D than what we are getting [from diet and sun exposure]," Recker says. "What is not agreed upon is how much more."

The Institute of Medicine recommends that most Americans need no more than 600 international units (IU) of vitamin D a day. People 71 and older may need 800 IU, it says. This level is enough for bone health, it says.

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