Vitamin D deficiency is a common problem. The principal source of vitamin D for humans is solar exposure, with cutaneous synthesis of vitamin D by photoconversion of 7-dehydrocholesterol in the skin to pre-vitamin D3. Latitude, altitude, season, skin pigmentation, and age are recognized factors that influence how much vitamin D can be made by solar exposure. Surprisingly, Vitamin D deficiency has been described in people dwelling in southern Florida and in surfers in Hawaii. We hypothesize that genetic variations in vitamin metabolism accounts for these differences.