Sunlight Exposure Guidelines May Need to Be Revised, New Research Shows

Priscilla Lynch 

September 30, 2021

Previously published solar exposure guidelines for optimal vitamin D synthesis based on a study of skin samples may need to be revised, according to new research published in  PNAS .

The association between specific ultraviolet (UV)B wavelengths and vitamin D production was determined more than 30 years ago in skin samples (ex vivo). However, the finding is less well established and there have been doubts about its accuracy. These doubts compromise risk/benefit calculations for optimal solar exposure.

The new research, led by King’s College London (KCL), has tested the optimum UV radiation (UVR) wavelengths for human skin production of vitamin D in sunlight. They measured serum 25-hydroxyvitamin D3 levels in 75 healthy young volunteers before, during and after partial- or full-body exposure to five different artificial UVR sources with different amounts of UVB radiation to weigh the trade-off between the benefits of solar exposure, which include vitamin D synthesis, versus the risks of sunburn and skin cancer.

They then compared their results with those that would be predicted from the old ex vivo vitamin D study and found that the previous study was not an accurate predictor of the benefits from UVR exposure.

The authors recommend a simple systematic correction of the ex vivo wavelength dependency for vitamin D. The new study means that many risk/benefit calculations for solar UVR exposure must be reviewed with a revised version of the wavelength dependency for vitamin D.

“Our study shows that risk versus benefit calculations from solar exposure may need to be re-evaluated. The results from the study are timely because the global technical committee, Commission internationale de l'éclairage, that sets UVR standards will be able to discuss the findings of this paper to re-evaluate the wavelength dependency of vitamin D. Further research from our group will determine the risk/benefit calculations,” said study author Prof Antony Young, KCL.

Young AR, Morgan KA, Harrison GI, Lawrence KP, Petersen B, Wulf HC, Philipsen PA. A revised action spectrum for vitamin D synthesis by suberythemal UV radiation exposure in humans in vivo. Proc Natl Acad Sci USA. 2021;118(40):e2015867118. doi: 10.1073/pnas.2015867118. PMID: 34580202

This article originally appeared on Univadis, part of the Medscape Professional Network.

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