Despite the importance of the sun for vitamin D synthesis, it is prudent to limit exposure of skin to sunlight [ 19 ] and UV radiation from tanning beds [ 21 ]. UV radiation is a carcinogen responsible for most of the estimated million skin cancers and the 8,000 deaths due to metastatic melanoma that occur annually in the United States [ 19 ]. Lifetime cumulative UV damage to skin is also largely responsible for some age-associated dryness and other cosmetic changes. The American Academy of Dermatology advises that photoprotective measures be taken, including the use of sunscreen, whenever one is exposed to the sun [ 22 ]. Assessment of vitamin D requirements cannot address the level of sun exposure because of these public health concerns about skin cancer, and there are no studies to determine whether UVB-induced synthesis of vitamin D can occur without increased risk of skin cancer [ 1 ].