I've done some research on the Vitamin D deficiency and learned several interesting things. One is that the increased use of high level sunscreens, while providing a benefit in terms of cutting down on skin cancers, has resulted in an increase in Vitamin D deficiency. For me, I don't get outdoors enough, and when I do I always wear sunscreen as I have very fair skin.
The other fact I didn't know is that people who are overweight, like myself, have a higher degree of the deficiency. Evidently the more fat cells you have the harder time your body has creating and utilizing Vitamin D.