Solar UV doses of young Americans and vitamin D3 production

Abstract

Background: Sunlight contains ultraviolet B (UVB) radiation (290-315 nm) that affects human health in both detrimental (skin cancers) and beneficial (vitamin D3) ways. Serum 25-hydroxyvitamin D concentrations from young Americans (≤ 19 years) show that many have deficient (< 50 nmol/L, 20 ng/mL) or insufficient (< 75 nmol/L, 30 ng/mL) vitamin D levels, indicating that they are not getting enough sun exposure. Those findings are in conflict with some calculated, published values that suggest people make "ample" vitamin D3 (~ 1,000 IU/day) from their "casual," or everyday, outdoor exposures even if they diligently use sunscreens with sun protection factor (SPF) 15.

Objective: We estimated how much vitamin D3 young Americans (n = ~ 2,000) produce from their everyday outdoor ultraviolet doses in the North (45°N) and South (35°N) each season of the year with and without vacationing.

Methods: For these vitamin D3 calculations, we used geometric conversion factors that change planar to whole-body doses, which previous calculations did not incorporate.

Results: Our estimates suggest that American children may not be getting adequate outdoor UVB exposures to satisfy their vitamin D3 needs all year, except some Caucasians during the summer if they do not diligently wear sunscreens except during beach vacations.

Conclusion: These estimates suggest that most American children may not be going outside enough to meet their minimal (~ 600 IU/day) or optimal (≥ 1,200 IU/day) vitamin D requirements.

Figure 1

Average estimated vitamin D₃ production by American children with skin type II according to age (years), sex, season, sunscreen use, and residence in the northern (45°N; A) or southern (35°N; B) United States.

Figure 2

Average estimated vitamin D₃ produced in children (≤ 19 years of age) from everyday outdoor UV exposures in the northern (45°N; A) or southern (35°N; B) United States, according to Fitzpatrick skin type and season (without use of sunscreen with SPF ≥ 15).

Figure 3

Average estimated vitamin D₃ made by U.S. children (≤ 19 years of age) during the summer according to skin type and vacation length (at latitude ~ 40°N in the continental United States). We assumed people use the equivalent of SPF 4 sunscreen during beach vacations.