Sunlight exposure guidelines may need to be revised
King's College London
A
study by researchers from King's College London, with support from the NIHR
Guy's and St Thomas' Biomedical Research Centre, has tested the optimum
ultraviolet radiation (UVR) wavelengths for human skin production of vitamin D
in sunlight.
UVR
from sunlight can cause sunburn and skin cancer, however, it is the most
important source of vitamin D that is essential for healthy bone development
and maintenance.
Public health advice on sunlight exposure takes both risk and benefits into account. Calculating the potential risks and benefits from sunlight exposure is not simple because the health outcomes from UVR exposure vary considerably with wavelength within the sun's UVR spectrum.
For example, the sun's UVR contains
less than 5% short wavelength UVB radiation but this is responsible for over
80% of the sunburn response. Each health outcome from solar exposure has its
own unique wavelength dependency.
The association between specific UVB wavelengths and vitamin D production was determined more than thirty 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.
Researchers
led by the Professor Antony Young from King's College London measured blood
vitamin D 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 the previous study is
not an accurate predictor of benefit 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.
Professor
Antony Young said: "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."
