Vitamin D -vs- Erythema: Effects of Solar Angle & Artificial Sources

Abstract

Vitamin D production in human skin is a documented clinical benefit from sunlight exposure. This study compares the spectral efficacy for vitamin D production -vs-erythema. Sunlight spectra at various solar altitudes are compared to several clinically available UV sources. We found that as solar altitude decreases effective irradiance for vitamin D production declines faster than erythemal efficiency. Dermatological recommendations limiting sun exposure to hours when one’s shadow is longer that one’s height are contraindicated for making vitamin D. Our analysis of low angle sunlight (≤30°) found the spectral risk for erythema exceeds the vitamin D benefit. Seasonal vitamin D deficiencies persist in northern latitudes where solar zenith is too low to produce adequate vitamin D for several months per year. People living at these latitudes, or others requiring dietary supplementation, may also benefit from supplemental UV exposure. While all sources emitting UVB produce Vitamin D in human skin, emission of UVA or UVC may elicit additional undesirable effects. Our spectral analysis suggests that a simple filtered intermediate pressure mercury source may be optimal for UV augmentation at home or in the clinic for prescribed vitamin D therapy.