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There's one vitamin you really need in winter

Monday - 1/27/2014, 7:07am  ET

WASHINGTON - The lack of sunlight in the winter means a lot of us may be getting dangerously low in vitamin D.

It is the only vitamin that is produced by sunlight hitting skin. And while it is present in a few foods - such as fish, eggs and soybeans - and added to others, this is one vitamin where supplements work best.

"Vitamin D deficiency, I would say, is probably the number one deficiency that we see," says Clair LeBrun, a nutritionist with GW University Hospital and the GW Medical Faculty Associates.

There is some debate over how much Vitamin D is needed. LeBrun says it helps protect the immune system, particularly against colon, breast and ovarian cancers.

But D is perhaps best known for its connection to healthy bones. The National Institutes of Health says people who get too little D may develop soft, brittle bones, and calcium with D helps older adults prevent osteoporosis.

Vitamin D deficiency can be detected by a simple blood test. And LeBrun says for most of us a little supplement of D "in the order of maybe 1000 to 2000 IUs" is sufficient.

The Office of Dietary Supplements at NIH says 4000 IUs a day is the safe upper limit for adults and children over nine. NIH also says problems overdoing it can potentially occur with supplements, but not with that natural source of vitamin D, the sun. That's because the body naturally limits the amount of D it produces from sun exposure.

The risks of running a D deficiency are known. But recent research indicates that people with healthy levels in their bloodstream don't get any extra benefit from taking vitamin D supplements.

A New Zealand study published in the journal Lancet Diabetes and Endocrinology questions the effectiveness of vitamin D supplements for those whose blood levels are in the OK range. It says those supplements don't reduce their risk of hear disease, stroke or cancer.

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