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Are the Benefits of Vitamin D Overhyped?

2 Studies Find Little Evidence That Vitamin D Prevents Heart Disease or Cancer
By
WebMD Health News
Reviewed by Laura J. Martin, MD

Dec. 19, 2011 -- Another day, and another vitamin has failed to live up to all of its hype. This time it’s vitamin D.

The reality check is coming from two new research reviews published in the Annals of Internal Medicine.

The reviews, which looked at hundreds of previous studies of the “sunshine vitamin,” conclude that there’s little evidence that vitamin D protects against cancer or heart disease.

They also show that vitamin D doesn’t prevent fractures when it’s taken alone. Pairing vitamin D with extra calcium does appear to help prevent broken bones in the elderly, however.

“For many years, the enthusiasm for vitamin D has outpaced the evidence,” says JoAnn Manson, MD, DrPH, who heads the division of preventive medicine at Brigham and Women’s Hospital in Boston.

“The evidence is actually fairly thin,” especially for any benefits beyond bone health, she says.

To help fill the knowledge gap, Manson is mounting a nationwide trial that will test vitamin D and fish oil for the prevention of heart attacks and cancer. She was not involved in the reviews.

Is Vitamin D a Dud?

In recent years, vitamin D has been touted as a nutritional superstar.

Beyond its well-known role as a bone builder, studies have suggested that high levels of D, usually achieved by taking supplements, may do everything from reducing chronic pain to preventing the common cold.

At the same time, other reports have found that as many as half of all adults have less than ideal blood levels of D.

That has sent sales of vitamin D blood tests and supplements soaring.

But experts say science doesn’t yet support the use of the high doses that many people may be taking.

Last year, the Institute of Medicine increased the recommended dietary allowance (RDA) of vitamin D for children and adults ages 1-70 to 600 international units (IU), and adults over 70 to 800 IU. But the agency also said many people already get that much from sun exposure and from foods like fish and fortified dairy products.

But the promise of D is so powerful that many policy makers continue to consider emerging evidence.

The latest is the U.S. Preventive Services Task Force, which is set to update its recommendations on vitamin D for cancer and fracture prevention in January. They commissioned one of these two new evidence reviews.

Vitamin D, Cancer, and Fractures

For that review, researchers at Tufts University reanalyzed data from more than 40 studies on vitamin D.

They set out to answer several key questions:

  • Does vitamin D, taken with or without calcium, affect the risk for cancer or broken bones?
  • Are high or low blood levels of vitamin D linked to a person’s risk for cancer or broken bones?
  • Are there harms linked to taking extra D?

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