Dermatologists Think it's Time to End Our Reliance on the Sun as a Major Source of Vitamin D

Vitamin D levels have dramatically decreased among Americans in the past two decades, according to a recent study reported in the Archives of Internal Medicine. "We found a marked increase in vitamin D deficiency over the past two decades," said lead researcher Dr. Adit Ginde, an assistant professor of surgery at the University of Colorado Denver School of Medicine. "Over three out of every four Americans now have vitamin D levels below what we believe is necessary for optimal health.

It is now recognized that vitamin D insufficiency and deficiency are common in elderly people, especially those who are not exposed regularly to sunlight due to infirmity or those who live at northern latitudes where there is insufficient sunlight-mediated vitamin D exposure in the winter months.

The primary function of vitamin D is to keep serum calcium and phosphorus concentrations within the normal range to support strong bones and maintain vital cellular functions. In children, vitamin D deficiency causes the bone-development disorder known as rickets. In adults, insufficient vitamin D can cause weakened bones (osteomalacia) or brittle bones (osteoporosis), increasing the risk of bone fractures.

For most people, the primary source of vitamin D is casual exposure to sunlight. During sunlight exposure, ultraviolet B photons (UVB) transform a form of cholesterol (7-dehydrocholesterol) found in the skin into previtamin D-3, which, in turn, is transformed via thermal isomerization into vitamin D-3 (cholecalciferol).

This natural production of vitamin D varies with the levels of skin exposure to UVB, which can be influenced by latitude, season, time of day, and air pollution. In northern latitudes, there is insufficient sunlight during the winter months for the skin to produce significant amounts of vitamin D. And because glass absorbs UVB radiation, exposure to sunlight through windows does not result in any production of vitamin D. Sunscreens also block the skin's absorption of UVB radiation, and studies have shown serum vitamin D levels in subjects who use sunscreen to be significantly lower than control subjects who did not use sunscreen.

A new review by dermatology experts suggests that supplements and diet, rather than sunlight, should be one’s source of vitamin D. The dermatologists suggest that the trade-off between obtaining vitamin D from sunlight exposure and the effects of photo-aging and skin cancer was sensible in our past, when life spans were not long. But in today's society, where life spans have doubled, and potentially 30% of Caucasians will develop skin cancer, the trade-off no longer makes sense. The conclusion is partly in response to recent research that proposed 10 to 15 minutes of unprotected exposure to midday sun as a good source of vitamin D.

Vitamin D supplements such as fish liver oil or multivitamin supplements supplying at least 400 IU of vitamin D per day may be the most practical way to ensure adequate levels of this essential vitamin.