Sun exposure and vitamin D sufficiency

摘要

Ultraviolet radiation is a carcinogen that also compromises skin appearance and function. Because the ultraviolet action spectra for DNA damage, skin cancer, and vitamin D3 photosynthesis are identical and vitamin D is readily available from oral supplements, why has sun protection become controversial? First, the media and, apparently, some researchers are hungry for a new message. Second, the controversy is fueled by a powerful special interest group: the tanning industry. This industry does not target the frail elderly or inner-city ethnic minorities, groups for whom evidence of vitamin D3 insufficiency is strongest, but rather fair-skinned teenagers and young adults, who are at highest risk of ultraviolet photodamage. Third, evolution does not keep pace with civilization. When nature gave humans the appealing capacity for cutaneous vitamin D3 photosynthesis, life expectancy was <40 y; long-term photodamage was not a concern; and vitamin D3 deficiency, with its resulting skeletal abnormalities (rickets), was likely to be fatal in early life. In the 21st century, life expectancy approaches 80 y in developed countries, vitamin D3 is available at the corner store, and the lifetime risk of skin cancer is 1 in 3 among white Americans. Medical and regulatory groups should avoid poorly reasoned, sensationalistic recommendations regarding unprotected ultraviolet exposure. Instead, they should rigorously explore possible cause-and-effect relations between vitamin D3 status and specific diseases while advocating the safest possible means of ensuring vitamin D3 sufficiency.