The April, 1999 issue of Nature contains an article about researchers at the University of Michigan, who have found that ultraviolet radiation from the sun blocks skin cells’ ability to recognize and respond to retinoic acid (skin cells make retinoicacid from retinal—a form of vitamin A). In essence, ultraviolet radiation causes a functional vitamin A deficiency in human skin.
According to Gary J. Fisher, Ph.D., U-M senior associate research scientist in dermatology and the study’s co-author, eight hours after skin was exposed to UV radiation the amount of retinoicacid receptor messenger RNA and protein was almost ¾ lower than control levels. This reduction lasted for 24 hours. Vitamin A is required for normal skin development and function; this reduction of the nutrient is harmful to skin. Daily exposure to the sun robs the skin does of adequate time to recover; the functional vitamin A deficiency in the skin is perpetuated. In the study, the levels rebounded after 16 hours if the skin was treated with retinoic acid before the sun exposure. Treating the skin after the ultraviolet exposure had no effect.
Ultraviolet radiation triggers production of enzymes called metalloproteinases, which break down collagen and elastin. Collagen and elastin are important to skin structure and integrity. The body does repair the damage, but the process is imperfect, leading to wrinkled, sun-damaged skin. Also, the production of metalloproteinasesmay promote skin cancer. More research is needed to understand the relationship between vitamin A and the enzymes that destroy collagen. Vitamin A may offer some protection from this process. It is too early to tell.
An interesting footnote to this story is some research done in 2002 supports this idea. Use of topical tazarotene, a vitamin A derivative, has significant potential for the prevention of basal cell carcinoma in people predisposed to the disease, according to a study presented at the American Association for Cancer Research’s (AACR) first annual Frontiers in Cancer Prevention Research meeting. The researchers found an 85% inhibition of both tumor number and size in the tazarotene-treated mice compared to mice administered a placebo. Tazarotene is currently on the market for the treatment of acne and psoriasis.