Can Vitamin D Prevent the Flu?

Claim: “The One Vitamin that Will Stop Flu in Its Tracks,” proclaims

What’s in it: Vitamin D.

Cost: About $1.50 a month for 1,000 IU a day.


The facts: Vitamin D increases the production of antimicrobial peptides (small protein-like natural antibiotics) in the body’s cells. And in two U.S. studies, people with higher vitamin D levels in their blood had a lower risk of upper respiratory infections. Does that mean that taking vitamin D can stop the flu (or a cold)?

Japanese researchers gave 334 children either 1,200 IU of vitamin D or a placebo every day from December through March. The vitamin D takers had six cases of the flu for every ten cases in the placebo takers.

But three trials in adults — using 400 IU a day for six months, 800 IU a day for 11 to 25 months, or 2,000 IU a day for three months — all came up empty. In none of the studies did those taking vitamin D have fewer cases of the flu or other respiratory infections than similar people who were given a placebo.

Bottom line: The evidence that vitamin D can prevent colds or the flu is meager.

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