Vitamin D is a really hot topic in research right now, and for good reason. More and more research is showing how important vitamin D is to our health. There are studies showing that high blood levels of vitamin D are associated with a dramatically reduced risk of cancer, a reduced risk of depression, improved bone density, improved immune function, and improved blood pressure.  (For adults, an optimal level of vitamin D is one that's between 45-50 ng/ml or 115-128 nmol/l; a high level is on the upper end of these ranges.)

Vitamin D may also be the key to promoting a healthy weight. One study in the Journal of Endocrinological Investigation found that there was an inverse association between serum vitamin D and body fat, and that fifty-one percent of morbidly obese women had a vitamin D deficiency, compared to 22 percent of non-obese women. This becomes even more of a problem during the winter months, when sunshine seems to disappear.

The U.S. Recommended Dietary Intake for vitamin D is 400 International Units (IU). However, research is suggesting that may not be enough. In fact, a recent study in the American Journal of Clinical Nutrition suggests that doses of 3,800 to 5,000 IU may be needed to maintain optimal blood levels, as the body doesn't absorb all it takes in. The official safe upper-limit (UL) for vitamin D intake is 2,000 IU, although many researchers are now saying this is much too conservative and it should be reset to 10,000 IU. However, scientific organizations are slow to change their recommendations, so it may be a while before the official UL is reset to a higher level.