 Actually, vitamin D is a pro hormone found in things like mackerel, tuna, sardines, most of the oily fishes. You get most of your vitamin D from the sun, probably 80 to 90 percent of it, but that certainly is not enough in order to get adequate levels of vitamin D. Most dermatologists in today's market certainly recommend a sun protection factor and certainly that prevents one from getting the vitamin D that's necessary. One of the most important functions of vitamin D certainly would be for the absorption of calcium to increase bone density, but you certainly need that along with things like phosphorus, magnesium, vitamin A, zinc, etc. Well approximately 90 percent of the population are deficient in vitamin D, and the best way to really find out is by doing a test. There are several companies that do tests, and two of those companies would be ZRT laboratories and also Spectrocell, and they will give you an accurate indication as to what your vitamin D levels are. They should be somewhere around 60. Now the normal recommendation is 30 or above, but that certainly is not enough. Certainly around 60 would be more appropriate.