At the moment, there's a great deal of interest in Vitamin D, and there's a growing body of research on its known and potential benefits. Some of these links will take you to research that, at this stage, should be taken with a large grain of salt. Everything from its effects on insulin sensitivity and fat loss to bone density and increased testosterone levels in men are being looked at. Here are some links, knock yourself out:
http://www.ncbi.nlm.nih.gov/pubmed/21154195
http://www.ncbi.nlm.nih.gov/pubmed/19655244
http://www.ncbi.nlm.nih.gov/pubmed/20498201
http://www.umm.edu/altmed/articles/vitamin-d-000340.htm
http://www.ncbi.nlm.nih.gov/pubmed/18269634
http://www.ncbi.nlm.nih.gov/pubmed/21154195
http://www.scribd.com/doc/37119595/D...ul-weight-loss
http://www.nutritionandmetabolism.com/content/7/1/28
On a related note: after a routine physical, some blood work showed that my Vitamin D levels were at the lower end of the reference range. This was about a month after I had experienced a sudden break in my foot while walking down some stairs outside my house, and a few months after I'd started having intermittent pain in the same part of that foot. These two events taken together were enough to compel me to start supplementing Vitamin D. Clinically, up to 50,000 I.U. weekly has been found to be safe. For the average person, that'd be going a bit overboard. For those who are deficient, 3,000-5,000 I.U. a day is the common recommendation. It's cheap and safe to take, so it won't hurt (and could help) to supplement with it.
-S.