A revised action spectrum for vitamin D synthesis by suberythemal UV radiation exposure in humans in vivo

• Published in: Proceedings of the National Academy of Sciences - PNAS 2021-10, Vol.118 (40), p.1-8
• Main Authors: Young, Antony R., Morgan, Kylie A., Harrison, Graham I., Lawrence, Karl P., Petersen, Bibi, Wulf, Hans Christian, Philipsen, Peter A.
• Format: Article
• Language: English
• Subjects: Adult; Biological activity; Biological Sciences; Blue shift; Calcifediol - blood; Dose-Response Relationship, Radiation; Erythema; Erythema - etiology; Humans; Irradiation; Radiation effects; Risk analysis; Skin - metabolism; Skin - radiation effects; Spectra; Synthesis; Ultraviolet radiation; Ultraviolet Rays; Vitamin D; Vitamin D - biosynthesis; Vitamin D3; Weighting functions; Young Adult
• ISSN: 0027-8424; 1091-6490; 1091-6490
• DOI: 10.1073/pnas.2015867118

Action spectra are important biological weighting functions for risk/benefit analyses of ultraviolet (UV) radiation (UVR) exposure. One important human benefit of exposure to terrestrial solar UVB radiation (∼295 to 315 nm) is the cutaneous synthesis of vitamin D₃ that is initiated by the photoconversion of 7-dehydrocholesterol to previtamin D₃. An action spectrum for this process that is followed by other nonphotochemical steps to achieve biologically active vitamin D₃ has been established from ex vivo data and is widely used, although its validity has been questioned. We tested this action spectrum in vivo by full- or partial-body suberythemal irradiation of 75 healthy young volunteers with five different polychromatic UVR spectra on five serial occasions. Serum 25-hydroxyvitamin D₃ [25(OH) D₃] levels, as the most accurate measure of vitamin D₃ status, were assessed before, during, and after the exposures. These were then used to generate linear dose–response curves that were different for each UVR spectrum. It was established that the previtamin D₃ action spectrum was not valid when related to the serum 25(OH)D₃ levels, as weighting the UVR doses with this action spectrum did not result in a common regression line unless it was adjusted by a blue shift, with 5 nm giving the best fit. Such a blue shift is in accord with the published in vitro action spectra for vitamin D₃ synthesis. Thus, calculations regarding the risk (typically erythema) versus the benefit of exposure to solar UVR based on the ex vivo previtamin D₃ action spectrum require revision.