A new study has found no evidence that taking a vitamin D supplement can reduce the chance of catching a cold.
Dr David Murdoch of the University of Otago, New Zealand, and colleagues explain that some observational studies have found that people with more vitamin D in their blood serum have fewer upper respiratory tract infections, such as colds. But clinical trials have shown unclear results.
So they recruited 322 healthy adults who randomly received a dose of 200,000 IU (international units) of vitamin D, then 200,000 IU a month later, then 100,000 IU each month, or placebo given in the same way, for 18 months. Participants’ levels of serum 25-hydroxyvitamin D (shortened to 25-OHD) were measured regularly.
Although vitamin D supplementation led to a rise in serum 25-OHD, there was no statistically significant difference in the rate of upper respiratory tract infections between the groups.
There were also no differences in the number of days of missed work as a result of upper respiratory tract infections, or the duration or severity of symptoms. Time of year did not affect the results, neither did the participants’ initial 25-OHD levels.
The study is published in the Journal of the American Medical Association today (October 3).
"Further research is required to clarify whether there is benefit from supplementation in other populations and with other dosing regimens," the authors add.
In response to the findings, Dr Jeffrey Linder of Brigham and Women’s Hospital and Harvard Medical School, Boston, said: "Results suggest that vitamin D should join the therapies listed in the Cochrane reviews as being ineffective for preventing or treating upper respiratory tract infections in healthy adults."
Murdoch, D. R, et al. Effect of Vitamin D Supplementation on Upper Respiratory Tract Infections in Healthy Adults: The VIDARIS Randomized Controlled Trial. Journal of the American Medical Association October 3 2012 doi:10.1001/jama.2012.12505
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