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And I'm Renee Montagne.

We've got some advice about how much vitamin D you really need this morning. It's become popular to take high doses of vitamin D. Experts at the Institute of Medicine now say there's no need to do that. NPR's Richard Knox has more.

RICHARD KNOX: The Institute of Medicine panel says people shouldn't believe claims that big doses of vitamin D prevent cancer or heart disease, diabetes, the flu, autism, or immune disorders such as multiple sclerosis.

Dr. CLIFF ROSEN (Institute of Medicine): The Internet will say vitamin D, you know, has all these benefits. But the evidence really isn't there.

KNOX: That's Dr. Cliff Rosen of Maine Medical Center in Portland, one of the 14 panel members. The only solid evidence, Rosen says, is that vitamin D is necessary for healthy bones. The panel found no national epidemic of vitamin D deficiency. That's what proponents of high-dose supplements believe. And many of the Institute of Medicine experts thought it might be true.

Dr. ROSEN: It was very surprising. I think there were a lot of us who came in thinking that requirements should be much higher or that the blood levels were not nearly as high. But it's very good news for the general population.

KNOX: The panel did raise the recommended daily intake of vitamin D from what it was 13 years ago. It now says children and most adults need 600 international units a day. People over 70 need to take in 800 units. That's two to three times more than before. But Rosen concedes that many of his colleagues will say the new recommendations are still way too low.

Dr. ROSEN: In the real world, people are taking 1,000, 2,000, up to 4,000 units a day.

KNOX: The panel is worried that people who take big doses of vitamin D may actually be doing themselves harm, though the evidence for that is scanty. It's understandable that many people, including nutrition scientists, worry about vitamin D deficiency. Humans make vitamin D when they're exposed to sunlight, but most of us are covered up most of the time, or stay inside.

And it's hard to get enough in the diet. That's why milk and orange juice are fortified with D. But Dr. JoAnn Manson of Harvard, another member of the Institute of Medicine panel, says vitamin D is just the latest in a long line of supplement fads.

Dr. JOANN MANSON (Institute of Medicine): Years ago, there were many of my Harvard colleagues taking high doses of vitamin E supplements, beta-carotene, folic acid, selenium, and down the line.

KNOX: All of those turned out to be busts. Some were actually harmful.

Dr. MANSON: It's extremely important that the enthusiasm not get ahead of the evidence.

KNOX: One doctor who advocates high doses of vitamin D isn't backing away from his conviction that most people need at least 3,000 units a day. Dr. Michael Holick says that's what he takes and what he recommends to his patients.

Dr. MICHAEL HOLICK (Boston University): Now they're recommending three times what we recommended in 1997. I suspect a decade from now that they're going to recommend another higher increase.

KNOX: Meanwhile, the new report gives a lot of people something to chew on. One of them is Philomena Quinn. She's JoAnn Manson's office manager at Brigham and Women's Hospital in Boston.

Ms. PHILOMENA QUINN (Brigham and Women's Hospital): Vitamin D now has been in the news a lot. It's been in the magazines a lot. Been in medical journals a lot. So I thought, hmm, maybe I should start taking this. So I started taking it about a year ago.

KNOX: So you're not taking it because you have something? You're taking it because you want to prevent something?

Ms. QUINN: No. Right. Well, I'm taking it, you know, to hedge your bets. You never can tell.

KNOX: Quinn didn't know about the new results until yesterday. She tells her boss she'll have to think about what to do.

Ms. QUINN: Well, you know, I'm going to have to read this report really seriously. But I probably would scale back.

KNOX: And that's what you want people to do, right?

Dr. MANSON: Exactly. Just take a look at the evidence and require that there be adequate evidence to support anything that you're doing.

KNOX: Especially, Manson says, if it involves a high-dose dietary supplement like vitamin D.

Richard Knox, NPR News, Boston

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