Solar UV doses of adult Americans and vitamin D(3) production

Sunlight contains UV radiation that affects human health in both detrimental (skin cancers) and beneficial (vitamin D(3)) 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 dietary sources or sunlight. Those findings are in conflict with calculated values from the American Academy of Dermatology who insist people make "ample" vitamin D(3) (≥1,000 IU/day) from their "casual," or everyday, outdoor UV exposures even if they use sunscreens with sun protection factor 15.

We investigated this situation using the everyday outdoor UV doses of indoor-working adult Americans (∼7,000) in the north (45°N) and south (35°N) to calculate how much vitamin D(3) they produce each season with and without vacationing.

Only during the summer can skin type II Caucasian adults (21-59 yr) meet their minimum (600 IU/day) vitamin D(3) needs from everyday exposures, but only if they do not wear professional clothes or sunscreens (except beach vacations).

To do vitamin D(3) calculations properly, we used action spectrum and geometric conversion factors, not previously incorporated into other calculations.

Most adult Americans do not go outside enough to meet their minimum or optimum (≥1,200 IU/day) vitamin D(3) needs all year. The darker skin types (III-VI) and the oldest people (>59 yr) are at the highest risk for not making enough vitamin D(3) during the year from everyday outdoor exposures even with a 2-3 week summer vacation.