We love every season. But when the days are getting shorter, the dreaded flu season is just around the corner.

We learned from a recent article in Nature that the two might just be related. The winter flu season could be the result of our reduced exposure to sunlight, according to a review scheduled for the December issue of Epidemiology and Infection.

The evidence that shows that vitamin D (created when solar radiation strikes skin) plays an important role in our immune system includes:

One study, conducted in St Petersburg and repeated in Krasnodar, Russia, showed that young men inoculated with live attenuated influenza virus were eight times more likely to develop fever and evidence of an immune response just after the winter solstice then they were during the summer months.

Another showed that children in India with vitamin D levels of less than 10 nanograms per millilitre were 11 times more likely to have respiratory infections than those with higher levels of the vitamin.

And a series of studies from the 1930s showed that cod-liver oil, which is rich in vitamin D, can reduce viral infections by 50% in adults taking a daily dose over 4 months.

But the theory still needs rigorous testing before doctors can recommend vitamin D to treat or prevent the flu, says the study’s lead author, John Cannell. Seems to be a bit of a do-as-I-say-not-as-I-do situation: he himself takes several times the government’s recommended dose every day during the winter.

While we don’t condone popping excessive amounts of vitamins, we do think getting a little extra vitamin D couldn’t hurt. Especially if it involves, say, a trip to the sunny, sandy beaches of Mexico in early February. 

Story by Alisa Opar. This article originally appeared in Plenty in November 2006. The story was added to MNN.com in July 2009.

Copyright Environ Press 2006.