Vitamin D and the Skin

Vitamin D is a micronutrient, meaning it's needed by the body to maintain normal cell function, but only in small amounts. While the vitamin can be obtained from food sources, it's also synthesized in the skin in the presence of sunlight. For this reason, while vitamin D isn't involved in skin function or maintenance of skin health, it's nevertheless a critical part of skin cell physiology.

Formation

According to biochemists Reginald Garrett, Ph.D. and Charles Grisham, Ph.D., vitamin D forms when cholesterol is reacted by the body to produce a molecule called dehydrocholesterol. This chemical reacts with the UV rays in sunlight that are incident upon the skin to produce pre-vitamin D, which spontaneously converts to cholecalciferol, or vitamin D-3. Another form of vitamin D, called ergocalciferol, is produced when sunlight reacts with a plant hormone called ergosterol. Humans obtain ergocalciferol from plant food sources.

Function

Drs. Garrett and Grisham note that vitamin D is essential to calcium homeostasis, or the maintenance of constant blood calcium levels in the body. The vitamin works together with parathyroid hormone and calcitonin---also a hormone---to induce absorption of calcium from the digestive tract, deposit it in the bones and excrete it from the kidneys.

Considerations

Since UV light (particularly shorter-length UVB) is required for production of vitamin D, sufficient light exposure is essential to adequate vitamin production. The Vitamin D Council advises that it doesn't take much sunlight to produce lots of the vitamin---in fact, the Council states, just a few minutes in the full summer sun provides 100 times as much vitamin D as recommended each day by the government. It notes, however, that clothing, sunscreen lotion and glass windows or screens prevent the sun's rays from penetrating the skin and producing the vitamin.

Expert Insight

Anthropologist Nina Jablonski suggests that skin color may play a large part in vitamin D formation from the sun. Darker-skinned people produce more of the chemical melanin, which acts as a natural sunblock. This chemical not only protects them from burning when exposed to the sun's rays, it also reduces their ability to form vitamin D. Regardless, Jablonski's research suggests that living at polar latitudes is much more likely than having dark skin to result in vitamin D deficiency---even dark individuals are capable of forming the vitamin in sufficient concentrations given enough sunlight.

Warning

The Skin Cancer Foundation warns that the risks of sunlight far outweigh benefits of extra sun exposure---it suggests that purposely increasing exposure to sunlight in order to boost vitamin D production is dangerous to health and increases the risk of skin cancer. Instead, the foundation recommends "[getting] 1,000 IU (international units) of vitamin D a day from food sources like oily fish, fortified dairy products and cereals and supplements."