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A new study finds vitamin D can help reduce the risk of colds and flu. Researchers say it's some of the best evidence yet that vitamin D may have benefits beyond keeping our bones strong. So who knows? Maybe we need some in my family. But the question is should we take supplements to get more of it and how much? NPR's Allison Aubrey reports.
ALLISON AUBREY, BYLINE: It's long been known that vitamin D, which we get from the sunshine and from our diets, helps protect our bones. But in recent years, researchers have studied whether vitamin D may also boost immunity and cut the risk of sickness. Adrian Martineua of Queen Mary University of London says there are now 25 studies that include more than 10,000 participants that have tested whether vitamin D supplements can help protect against colds and the flu. And when he and his collaborators at Harvard Medical School put all the data together and analyzed it, they found taking extra vitamin D did seem to be beneficial.
ADRIAN MARTINEAU: The headline finding, the first thing we found, was that overall there was a modest protective effect of vitamin D against respiratory infections in the population as a whole.
AUBREY: Supplements cut the risk of colds and flu overall about 10 percent. But when they focused on people who were known to have very low levels of vitamin D, they found that, for them, taking a daily or weekly supplement had a bigger benefit.
MARTINEAU: What we found was that those with the lowest vitamin D levels, you can take a vitamin D supplement, you can reduce your risk of a respiratory infection by around 50 percent. It's quite a large effect.
AUBREY: Now, just after I interviewed Dr. Martineau yesterday, I thought to myself, well, it's cold, it's dark, and I haven't seen much of the sun. And everyone around me, including my editors, seems to be fighting off bad viruses. Maybe I should stop at the drugstore and pick up some vitamin D. But then I spoke to Steve Abrams. He's a physician and professor of pediatrics at the Dell Medical School at The University of Texas at Austin. He was part of an expert panel that wrote guidelines several years back on how much vitamin D children and adults in the U.S. should get.
STEVEN ABRAMS: The recommendation for most adults is that they have 600 units per day of vitamin D intake.
AUBREY: My first question to him was what dose of a supplement he takes.
ABRAMS: I don't actually take a supplement.
AUBREY: Abrams says, living in Texas, he sees a fair amount of sun, and he gets vitamin D from his diet.
ABRAMS: A glass of milk, an eight-ounce glass of milk for example, will provide a little over 100 units per day.
AUBREY: That's a chunk of what you need. And since milk and other dairy products - as well as many orange juices and cereals - are fortified, Abrams says these can all be good sources, too. The other excellent source is oily fish. One serving of salmon can provide almost a whole day's worth of vitamin D. Abrams says given that many Americans don't eat much fish and don't get enough sunshine, taking a multivitamin that contains vitamin D is a reasonable option.
ABRAMS: The standard multivitamins usually have 400 units per day.
AUBREY: So that's enough for many people but not for everyone. Monique Tello is a primary care doctor at Massachusetts General in Boston. She says lots of patients come in asking to be tested, and certain people are at higher risk of not getting enough vitamin D. This includes many postmenopausal women, those who cover their skin and people with conditions such as celiac disease.
MONIQUE TELLO: Those people should get tested. You know, we should have an idea of where their level's at and just make sure that it's acceptable.
AUBREY: Tello says when a screening test shows insufficient levels...
TELLO: I recommend that they take between 1,000 and 2,000 international units of vitamin D daily indefinitely.
AUBREY: And for people with a severe deficiency, Tello says there are cases when much higher doses are recommended - at least in the short term. Allison Aubrey, NPR News.
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