There is a growing body of evidence suggesting that taking high doses of vitamin D may effectively reduce the risk of getting respiratory infections like influenza or flu.

There is a theory that explains why flu peaks in certain reasons.   R. Edgar Hope-Simpson in 1981 proposed that a "seasonal stimulus" associated with solar radiation explained the seasonality of epidemic influenza, according to John J Cannell and colleagues of Atascadero State Hospital in California.

Cannell, who has studied the associations between vitamin D and diseases extensively, and colleagues published an article in the Dec 2006 issue of Epidemiology and Infection suggesting that the seasonal stimulus may be vitamin D.

Vitamin D plays an important role in innate immunity against viral infections including flu.   Studies showed that people who volunteered to receive attenuated influenza virus were more likely to develop fever and serological signs of an immune response in the winter.

In the winter, people get less exposure to sunlight and are more likely than in other seasons to have vitamin D deficiency or insufficiency, which is the reason for a weakened immune response against infections like flu.

In another article published in the Feb. 2008 issue of Virology Journal, Cannell and colleagues mentioned studies suggesting that taking high doses of vitamin D (2000 IU per day) for three days may completely eliminate the incidence of flu and colds.

In one study mentioned by Cannell et al., 104 post-menopausal African American women given vitamin D were three times less likely to report colds and flu than 104 controls.   Black men and women are more likely to suffer vitamin D deficiency because their dark skin makes absorption of ultraviolet rays difficult.

Editor's note:  Thank Dr. Cannell for sending us a reprint of his study on  vitamin D and flu epidemic.  A full report is available from http://virologyj.com/ mostviewed