Did you ever stop to wonder why we have a “cold and flu season” — that is, why do we tend to get these illnesses in the cold, dark winter? And surely you have noticed that some people are naturally resistant to colds and flu even while others around them are coughing, hacking, and spreading the viruses like mad. As science now tells us, the answer, or at least part of it, lies in the sunshine vitamin known as vitamin D.
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http://www.womentowomen.com/inflammation/vitamind-swineflu.aspx