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Medical Panel: Don't Go Overboard On Vitamin D

A man sunbathes in Malmo, Sweden, in July. Humans (and other animals) make vitamin D when exposed to sunlight. (AFP via Getty Images)

The Institute of Medicine is throwing cold water on the latest dietary supplement fad: big doses of vitamin D.

Humans make vitamin D when they are exposed to the sun. But many worry that clothing, indoor living and sunscreen are depriving most people from enough of the sunshine vitamin. It's also hard to get enough vitamin D from the diet, proponents say, despite fortification of milk and orange juice.

But the institute's Food and Nutrition Board, which makes official recommendations on dietary intake, says advocates of high-dose vitamin D are going overboard.

After two years of study and debate, the panel says children and most adults need 600 international units of vitamin D a day. People older than 70 need 800.

That's more than the previous targets, set 13 years ago, of 200 units a day for young adults, 400 for those older than 50.

But the new recommendations are much less than advocates of high-dose vitamin D claim is necessary. Many people believe daily doses of 1,000 to 4,000 units can prevent a long list of ailments -- cancer, heart disease, diabetes, influenza and other infections, autism, immune disorders such as multiple sclerosis, and more.

The Institute of Medicine panel rejects those claims. The only benefit, it says, is to maintain healthy bones.

"The evidence was inconsistent and inconclusive as to a benefit of vitamin D in preventing cancer, cardiovascular disease, diabetes, autoimmune disorders and many other health outcomes beyond bone health," says Dr. JoAnn Manson, chief of preventive medicine at Brigham and Women's Hospital in Boston and one of the 14 IOM panel members.

"The Internet will say that vitamin D has all these benefits," adds Dr. Cliff Rosen of Maine Medical Center in Portland, another panelist. "But the evidence really isn't there."

The panel also found no national epidemic of vitamin D deficiency. Many proponents of high-dose supplements believe there is one, and many of the IOM experts thought it might be true.

"It was very surprising," Rosen says. "I think there were a lot of us who came in thinking that requirements should be much higher or that [average American] blood levels were not nearly as high. But it's very good news for the general population."

The new report says people's blood levels of vitamin D don't need to be higher than 20 nanograms per milliliter of blood. Leading proponents aim for a blood level of 30 or even 40.

If 30 were the right number, more than half of the U.S. population could be considered deficient in vitamin D.

"Let's face it, everybody wants a number," Rosen says. "Everybody wants to know their vitamin D level these days. And so when you look and you say, 'Gee, my level's 25 and it should be 30, and it doesn't seem harmful to take a supplement and more is better, then I should be doing that.' And that's exactly what happened."

The Institute of Medicine experts worry that taking vitamin D in large doses over a long period might harm some people. The evidence is inconclusive, but the panel points to studies hinting at higher levels of pancreatic and esophageal cancer. Panelists say there's reason to worry about excess deposits of calcium in arteries from too much vitamin D.

Dr. Michael Holick of Boston University, who discovered the active form of vitamin D 40 years ago and is a leading proponent of high doses, isn't backing away from his conviction that most people need at least 3,000 units a day. That's what he takes, and what he recommends to his patients. Sometimes he prescribes 50,000 units of vitamin D a week.

"My recommendation is very simple," Holick says. "I don't see any downside to increasing your vitamin D intake. When I've been recommending for the past decade that people take more than the [officially recommended] 200 units, there was a lot of skepticism. Now they're recommending three times what we recommended in 1997.

"I suspect a decade from now that they'll be recommending another three- or fourfold higher increase," Holick predicts.

Members of the Institute of Medicine panel say that's possible -– if rigorous studies back up the proponents' claims. Manson is launching a $22 million federally financed study that will involve 20,000 people across the country. They will be randomly assigned to take daily doses of vitamin D and omega-3 fatty acid (linked in many studies to lower levels of heart disease) –- together or alone. Others will get placebo pills.

But it will be five or six years before the results of that study are ripe, Manson says.

The Institute of Medicine panel also reconsidered calcium intake, because vitamin D and calcium together are necessary for healthy bone development and maintenance throughout life.

The panel says children ages 1 to 3 need 700 milligrams of calcium a day, while those ages 4 to 8 need 1,000 milligrams. Adolescents need no more than 1,300 milligrams, while adults up to age 50 need 1,000 milligrams. Starting at age 51, women need 1,200 milligrams of calcium a day, as do both men and women older than 70.

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Transcript

STEVE INSKEEP, host:

It's MORNING EDITION from NPR News. Good morning. I'm Steve Inskeep.

RENEE MONTAGNE, host:

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 Transcript provided by NPR, Copyright NPR.

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