Vitamin D’s impact on infection

The sun (in moderation) is an excellent source of Vitamin D. Image: Pond Pond/Shutterstock

Low levels of sun exposure may be putting you at risk.

Spring has sprung, and that usually means that our thoughts can turn away from cold temperatures and sickness such as the flu. However,  your winter cold may have less to do with the temperature and more to do with the sun — or lack thereof. Researchers at Harvard University, US, found that vitamin D supplementation decreased the risk of respiratory infections among Mongolian school children who had low levels of vitamin D at the beginning of the study.

“Randomised, double-blind, placebo-controlled trials provide very strong evidence in support or refute the causality of a previously noted association,” says Carlos Camargo of Massachusetts General Hospital (MGH) and corresponding author of the paper. “In this case, the trial supports an anti-infective role for vitamin D in children with low baseline levels of the vitamin.”

Because vitamin D is naturally produced by the body in response to sunlight, maintaining adequate levels in winter is particularly challenging in areas such as Mongolia, which has significant seasonal variations in daily sunlight. In the study, Camargo and colleagues compared the number of winter respiratory infections among a group of children who received daily doses of vitamin D added to locally produced milk with that of a control group receiving the same milk without added vitamin D. The supplement was undetectable so that children, teachers, and local researchers could not tell which group received vitamin D.

Blood samples taken at the outset of the study revealed vitamin D deficiency in all participants, with average 25OHD levels around 7 ng/ml (17 nmol/L) in both groups, at the end of the seven-week treatment period. Differences between the two groups were significant, with those who received vitamin D averaging 19 ng/ml (47 nmol/L), which although still low was significantly higher than at the start of the trial. Based on reports from their parents, the children receiving vitamin D had about half the incidence of respiratory infections that the control group had.

“Research should continue on this important topic to better understand several other important questions”“such as the threshold where benefit is no longer apparent, the optimal dose and frequency, and other questions” Camargo says. “Our trial provides motivation that there really is a signal and that it’s worthwhile to continue down this track.”

So will this research change the way people will prepare themselves for the winter months? “Yes, some people will change,” insists Camargo. “But other will want more evidence. I’m optimistic that the results are true in a population with this level of vitamin D deficiency.”

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