Evidence suggests Vitamin D supplementation reduces the incidence of these diseases, yet there is a lack of research to prove it.

Vitamin D is formed by the action of Ultraviolet B (UVB) on precursor molecules in the skin. From skin, these molecules travel via the bloodstream to the liver and kidneys, where they are metabolized into active Vitamin D. There are 2 forms of Vitamin D: D2 can be found in fungi, plants, and invertebrates, while D3 is formed in vertebrates. Vitamin D3 is more active in humans. In addition to the synthesis of Vitamin D by the action of UVB on skin (exposure to sun), natural dietary sources can provide it as well. Oily fish (mackerel, salmon, sardines), mushrooms, and fortified milk, cereal, and bread.

Recent data document an "epidemic" of Vitamin D deficiency in some populations, especially breast-fed infants, housebound seniors, and darker-skinned individuals who form less Vitamin D in response to sunlight. For dermatologists, a serious concern is whether recommended sun protection may result in Vitamin D deficiency. While there is some controversy, most studies have concluded that sunscreen use is not associated with Vitamin D deficiency.

Current recommendations for Vitamin D supplementation will be revised this year to increase. Current standards suggest between 200 and 600 IU depending on age. In advance of the publication of newer guidelines, many doctors are recommending 1000 IU of Vitamin D supplementation daily for most adult patients. Unfortunately, it is difficult to get adequate supplementation with foods alone – an egg provides only 20 IU, a glass of milk 100 IU, and a serving of salmon 360 IU. Concerns regarding overdosing with supplemental Vitamin D, a fat-soluble vitamin, have been raised, but are generally unfounded with doses of 1000 IU per day. There are select circumstances, however, that require precaution: Parents of infants and small children should check with their pediatrician. Pregnant and breastfeeding women should consult their obstetrician before taking vitamin supplements. Patients with hypercalcemia or kidney disease should check with their internists before taking Vitamin D.

While sun exposure increases Vitamin D it can also cause skin to age by way of dry, mottled, wrinkled, old-looking skin. So the best advice in 2010 for most of us is this: use sun protection and take oral Vitamin D supplementation.