Investigative Analysis

Vitamin D Deficiency: Is There a Downside to Sunscreens?

February 2004

In the past 20 years, the use of sunscreen products has risen dramatically, due largely to the efforts of dermatologists to reduce the risk of skin cancers caused by the sun's damaging ultraviolet rays. But there's a growing body of evidence that there may be an unexpected downside to this skin cancer prevention measure: an increased risk for vitamin D deficiency.

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.

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. For many people, insufficient vitamin D can be addressed by increasing sun exposure before applying sunscreen, but it's important to do this in moderation due to the increased risk of skin cancer associated with excessive sun exposure, and this approach may be inadequate during the wintertime for people living at northern latitudes. During the winter months, 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.

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