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Study: Vitamin D supplements have no effect on the common cold

vitamin d supplement
CC/Flickr/Laura B. Dahl
The only proven health claim for vitamin D is that it promotes strong bones.

Few supplements have been hyped as relentlessly and breathlessly — and with as little hard evidence — as vitamin D. Claims have been made that taking the supplement will reduce the risk of a long list of health problems, from minor ailments like the common cold to major chronic diseases like heart disease, diabetes and cancer.

The only proven health claim for vitamin D is that it promotes strong bones. But, as the Institute of Medicine (IOM) pointed out in a 2010 report, the vast majority of us (even those of us living in northern altitudes) absorb sufficient amounts of the vitamin through the foods we eat and our brief exposures to sunlight.

Other health claims for vitamin D supplements have been based mostly on observational studies, which (as I’ve noted frequently in this blog) can show only a correlation between two things, not a cause-and-effect relationship. For the latter, we need randomized controlled clinical trials.

On Tuesday, the results of just such a clinical trial were published in the Journal of the American Medical Association (JAMA), and they weren’t what promoters of vitamin D were hoping for.

The study found that high doses of vitamin D do not reduce the incidence or severity of upper respiratory tract infections, including the common cold.

The study’s details

For the study, a team of New Zealand scientists randomized 322 healthy adults to receive either high monthly doses of vitamin D (200,000 IUs for two months, followed by 100,000 IUs for each month thereafter) or a placebo. The amount of vitamin D received by those in the treatment arm of the study was five times the recommended U.S. daily adult allowance of 600 IUs.

The pills were given directly to the participants at monthly meetings with the study’s staff. At those meetings, participants were asked if they had experienced a runny nose, nasal stuffiness, sore throat, cough or any other symptoms of upper respiratory tract illness. They were also instructed to call the staff when they did experience such symptoms so that a nasal swab could be taken to confirm that they had such an illness.

After 18 months (a period that covered two winter cold-and-flu seasons), the researchers found no statistically significant differences in the number of upper respiratory tract infections between the vitamin D and placebo groups. An average of 3.7 infections per person occurred in the vitamin D group compared with 3.8 in the placebo group.

Nor was there any difference in the severity or duration of the upper respiratory tract infections experienced by the two groups.

A few caveats

This study, like all studies, has several limitations. It includes a relatively small number of participants, for example, and the doses were prescribed monthly rather than daily. (This was done, in part, to ensure that participants actually took the pills.) It’s possible that vitamin D supplements would produce different results in other population groups or at other doses, the study’s authors say.

Indeed, they point out that in another randomized trial, Mongolian children with vitamin D deficiency who were given supplements of the vitamin experienced a 50 percent reduction in acute respiratory infections.

But, as the IOM emphasized in its 2010 report, very few people in the United States have vitamin D deficiency — despite the hype.

‘Ineffective’ and ‘questionable benefit’

In an editorial that accompanied the JAMA study, Dr. Jeffrey Linder of Brigham and Women’s Hospital and the Harvard Medical School in Boston, says that this study suggests that vitamin D supplements should now be relegated to the same category as other therapies for the common cold that have been shown to be “ineffective, have questionable benefit, or are associated with significant adverse effects.”

Those discredited treatments, he adds, include “Echinacea, zinc, steam inhalation, vitamin C, garlic, antihistamines, Chinese medicinal herbs, intranasal corticosteroids, intranasal ipratroprium, Pelargonium sidoides herbal extract, saline nasal irrigation, increasing fluid intake, and antivirals.”

And antibiotics, of course.

So, save your money this winter.

The study, which was funded by the Health Research Council of New Zealand, can be read in full on the JAMA website.

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