Academic journal article Environmental Health Perspectives

Solar UV Doses of Young Americans and Vitamin [D.Sub.3] Production

Academic journal article Environmental Health Perspectives

Solar UV Doses of Young Americans and Vitamin [D.Sub.3] Production

Article excerpt

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-hydroxy-vitamin 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 [D.sub.3] (~ 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 [D.sub.3] young Americans (n = ~ 2,000) produce from their everyday outdoor ultraviolet doses in the North (45 [degrees] N) and South (35 [degrees] 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 ( [greater than or equal to] 1,200 IU/day) vitamin D requirements.

Key WORDS: cancer, environment, sunlight, sunscreen, vitamin D. Environ Health Perspect 120:139-143 (2012). [Online 18 August 2011

Ultraviolet (UV) radiation (290-400 nm) in sunlight can affect people's health in both detrimental and beneficial ways. Short-term detrimental health effects include sunburn and immune suppression, and long-term detrimental health effects include cataracts, photoaging, and DNA damage with mutations that can lead to nonmelanoma and melanoma skin cancers. Beneficial health effects of UV radiation include medical detection and treatments of diseases such as cancers; possible reduction in the mortality from some cancers, including colon cancer (Garland et al. 1989), breast and prostate cancer (Freedman et al. 2002), and melanoma (Berwick et al. 2005); and vitamin D3 production (Holick et al. 1980).

Children may need more vitamin D3 than amounts recently recommended (600 IU/day) by the Institute of Medicine (2011) to maintain healthy muscles (Pfeifer et al. 2002), bones (Holick 2007), and general health (Heaney and Holick 2011; Holick 201 1). For example, the risk of type 1 diabetes may be significantly reduced in children if they take 2,000 IU/day of vitamin D supplements early in life (Ponsonby et al 2009; Zipitis and Akobeng 2008). Conversely, there is some evidence that infants who develop rickets, a consequence of vitamin D deficiency, are at increased risk of type 1 diabetes mellitus (Hypponen et al. 2001). Thus, correct levels of vitamin D may prevent or reduce the occurrence of type 1 diabetes mellitus (Harris 2005).

For most children, the major source of vitamin [D.sub.3] comes from exposing their skin to sunlight (Glerup ct al. 2000). In animals, yeast, fungi, and plants, sunlight forms either vitamin [D.sub.3] or [D.sub.2], both of which may be equally effective in maintaining human scrum levels of 25-hydroxyvitamin D [25(OH) D; D represents both [D.sub.2] and [D.sub.3]; Holick et al. 2008]. Vitamin [D.sub.3] production occurs in human skin when ultraviolet B (UVB; 290-33 5 nrn) photons convert 7-dehydro-cholesterol, or provitamin D3, made by kera-tinocytes to previtamin [D.sub.3] (MacLaughlin et al. 1982), which thermally isomerizes to vitamin [D.sub.3] (Holick et al. 1995b). Vitamin [D.sub.3] that forms in the skin and vitamin D2 or D3 from dietary sources are carried into the bloodstream by vitamin D-binding protein, an alpha 1 globulin. …

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