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Do vitamin D pills prevent colds? 10/12
(This article is adapted from ConsumerReports.org.)

Vitamin D is a hot seller in the supplement aisles, but it won't help you ward off or recover faster from the common cold. That's according to a study in the October 3 issue of the Journal of the American Medical Association.

In the randomized, double-blind placebo-controlled trial, 322 healthy men and women age 18 or older received either vitamin D pills or a placebo for 18 months, including two winter seasons. During that time, they also answered monthly questionnaires about their health and contacted researchers whenever they experienced cold symptoms.

There were 593 colds in the vitamin D group, and 611 in the placebo group, not a significant difference, according to the team led by researchers at the University of Otago in New Zealand.

The investigators also found no significant difference between the groups in the number of participants who had colds (3.7 per person in the vitamin D group and 3.8 per person in the placebo group, on average), duration of symptoms per cold (12 days in each group, on average), the number of days of missed work as a result of colds (less than a day in each group, on average), or the severity of colds.

"The fact that receptors for vitamin D exist in many organs and structures of the body has led to much speculation on the multifaceted prowess of this vitamin," said Marvin Lipman, M.D., Consumer Reports chief medical consultant. "But only randomized controlled clinical trials can turn such belief into truth."

Bottom line

Some prior research had hinted that vitamin D might improve immune function and possibly prevent respiratory infections like the common cold. But in this well-designed study, monthly doses of 100,000 international units of vitamin D (a dosing regimen more than 5 times the recommended daily allowance of 600 IU for adults ages 19 to 70) did not significantly reduce the incidence or severity of colds.

In Consumer Reports July 2011 survey on alternative therapies, prescription drugs beat a dozen other cold and flu treatments that readers used.

For the survey participants, over-the-counter medication also helped—it ranked as well as deep-breathing exercises and goldenseal. Insufficient clinical evidence exists to support the use of goldenseal or chiropractic for treating colds but there’s some evidence that echinacea, vitamin C, and zinc are possibly effective.

How much vitamin D is safe?

If you get some midday sun exposure during the warmer months and regularly consume vitamin D-rich foods, you probably don't need supplements. People who are middle-aged or otherwise at risk of vitamin D deficiency, including those who are overweight or have darker skin, might need supplements. Even then, the amount in most multivitamins is probably enough.

Good food sources of vitamin D include cod-liver oil, cooked button mushrooms, eggs, fortified milk and soy products, mackerel, sardines, and wild Alaskan or sockeye salmon.

If you decide to take vitamin D supplements, until research confirms the benefit of higher doses, stick with the Institute of Medicine’s recommendation: 600 IU for adults up to age 70 and 800 IU for those older than 70.

Always look for a vitamin D product with the "USP Verified" mark, which means it meets standards of quality, purity, and potency set by the nonprofit U.S. Pharmacopeia. For better absorption of the vitamin, take it with a meal containing some fat.

Related links

Effect of Vitamin D3 Supplementation on Upper Respiratory Tract Infections in Healthy Adults, Journal of the America Medical Association (JAMA). 10/12

Alternative health treatments. 7/11

The vitamin D dilemma. 5/11
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