Since I was diagnosed with Vitamin D deficiency I have been reading all I can about it. Did you know that Vitamin D is not a Vitamin at all? It is a hormone. And after reading about it I cant believe its not more popular.
Do you remember in the 60's and 70's when East Germany and the Soviet Union were dominating in the Olympics? Well part was due to Steroids, but a big part of their success was due to their knowledge of Vitamin D and athletic performance. The Germans had big sunlamp rooms where Soldiers and athletes would "tan" . The Vitamin D would then be made in the skin and sent to the blood stream.
Here is what Wikipedia says about Vitamin D:

"Vitamin D is a group of fat-soluble prohormones, the two major forms of which are vitamin D2 (or ergocalciferol) and vitamin D3 (or cholecalciferol).[1] The term vitamin D also refers to metabolites and other analogues of these substances. Vitamin D3 is produced in skin exposed to sunlight, specifically ultraviolet B radiation.

-Vitamin D plays an important role in the maintenance of organ systems.[2]
-Vitamin D regulates the calcium and phosphorus levels in the blood by promoting their absorption from food in the intestines, and by promoting re-absorption of calcium in the kidneys.
-It promotes bone formation and mineralization and is essential in the development of an intact and strong skeleton. However, at very high levels it will promote the resorption of bone.
-It inhibits parathyroid hormone secretion from the parathyroid gland.
-Vitamin D affects the immune system by promoting phagocytosis, anti-tumor activity, and immunomodulatory functions. "


Vitamin D is not found in sufficent amounts in food. You need to get sunlight. But avoid more than 30 minutes a day without sunscreen. (Moderation in all things)