Solar UV Doses of Adult Americans and Vitamin D3 Production

摘要

Background: Sunlight contains UV radiation that affects human health in both detrimental (skin cancers) and beneficial (vitamin D3) ways. An evaluation of the vitamin D status of adult Americans (22-40, 41-59, 60+ yr) show many have deficient or insufficient serum levels of 25-hydroxyvitamin D, indicating they are not getting enough from sunlight or dietary sources. Those findings are in conflict with calculated values that insist people make “ample” vitamin D3 (≥1,000 IU/day) from their “casual” or everyday outdoor exposures.Objective: We investigated this situation using the outdoor UV doses of indoor-working adult Americans (~7,000) in the north (45°N) and south (35°N) to calculate how much vitamin D3 they produce each season of the year with and without vacationing.Method: To do vitamin D3 calculations properly, we used action spectrum and geometric conversion factors, not previously incorporated into other calculations.Results: Few indoor-working adults over 21 yr meet their daily vitamin D needs from everyday outdoor exposures anytime during the year, including summer. Only a few “outdoorsy” Caucasians (22-60 yr) can meet their vitamin D3 needs (~2,000 IU/day) during the summer, but only if they do not wear sunscreens except on beach vacations.Conclusions: Most indoor-working adult Americans do not go outside enough to meet their vitamin D3 needs all year. Only some outdoor-working adults can make enough vitamin D3 without using sunscreen but other adults cannot, even with a vacation during the summer. Indoor-working African Americans can never make enough vitamin D3 during the year even with a 3-week vacation.