Optimising solar UV exposures for vitamin D3: comparing global and diffuse spectral UV

Abstract

[Abstract]: Currently, there is a major gap in the knowledge that is needed in order to optimise the beneficial effects related to ultraviolet (UV) radiation for vitamin D3 synthesis (UVD3) compared to reducing the biologically damaging overexposure to UV radiation. The aim of this paper is to investigate the use of diffuse (radiation that is scattered from all directions) UV to optimise UVD3 exposures and maximize the reduction of UVA exposures. Global and diffuse solar UV spectral data have each been collected in ten minute intervals during the Southern Hemisphere late spring and summer from 1 November 2006 to 28 February 2007. For a solar zenith angle (SZA) of approximately 5o, the observed maximum UVD3 irradiances were 0.80 W/m2 and 0.46 W/m2, for global and diffuse UV respectively. While the observed maximum UVA irradiances were 79.0 W/m2 and 36.2 W/m2, for global and diffuse UV respectively. For diffuse UV, the maximum ratio of vitamin D3 to UVA was 1.75% at a SZA of approximately 10o, whereas the maximum ratio for global UV was 1.27% at 10o. For SZAs of 25o and less, more UV radiation is contributed toward vitamin D3 than toward UVA exposure by utilising diffuse UV compared to global UV.