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

Research output: Contribution to journalArticlepeer-review

Antony R. Young, Kylie A. Morgan, Graham I. Harrison, Karl P. Lawrence, Bibi Petersen, Hans Christian Wulf, Peter A. Philipsen

Original languageEnglish
Article numbere2015867118
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number40
Published5 Oct 2021

Bibliographical note

Funding Information: ACKNOWLEDGMENTS. This is independent research commissioned and funded by the UK Department of Health Policy Research Programme (Vitamin D photosynthesis: Interactions with melanin and UVR spectrum, 091/0202) and European Community’s Seventh Framework (Grant Agreement 227020, ICE-PURE). The views expressed are those of the author(s) and not necessarily those of the Department of Health nor the European Community. We thank Rosie Gulliver and Rachel R. Harris for the irradiations of the volunteers and their excellent technical and logistics support. We also thank Dr. Robert Sarkany and Sister Trish Garibaldinos and their staff for access to clinical photodermatology facilities, Dr. Andrew Coleman for dosimetric support, and Prof. Mary Norval for reviewing our abstract. We also acknowledge support from the UK Department of Health via the NIH Research comprehensive Biomedical Research Centre award to Guy’s and St. Thomas’ NHS Foundation Trust in partnership with King’s College London and King’s College Hospital NHS Foundation Trust. Finally, we thank the endurance of all our volunteers. Publisher Copyright: © 2021 National Academy of Sciences. All rights reserved. Copyright: Copyright 2021 Elsevier B.V., All rights reserved.

King's Authors


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.

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