Is more sun the answer to low vitamin D?
13 August 2009
Research produced by the Department of Twin Research and Genetic Epidemiology, King's College London, has shown that vitamin D levels are lower in fair-skinned Caucasian women than in Caucasian women with darker skin types.
Low levels of vitamin D, the researchers say, could lead to detrimental health effects, including bone disorders and cancer. They suggest that current advice for fair-skinned people to avoid sun exposure may need to be revised.
"It's about a careful balance," says Dr Daniel Glass, lead author of the paper published in the journal 'PLoS One'. "It's still very important not to get sunburnt or stay in the sun for long periods without protection, but you need enough sun exposure to keep your vitamin D levels topped up: 10-15 minutes of sunshine a day could be enough to do this.
"The alternative is vitamin D supplementation, but the study showed that very few women took vitamin D supplements."
In the study, the researchers measured the levels of a form of vitamin D called 25-hydroxy-vitamin D in the blood serum of over 1400 Caucasian women recruited from the Twins UK Adult Twin Registry.
The women answered questions on their exposure to the sun and to sunbeds, and their experience of sunburn over their lives. Research nurses classified the twins' skin into one of four categories according to pigmentation.
The results showed that women with the darker skin types were significantly less likely to have low levels of vitamin D than those with lighter skin types. This finding is contrary to those of the majority of studies in the field, which report higher rates of vitamin D deficiency in people with more deeply pigmented skin.
In concordance with other studies, the researchers found that sunbed exposure and holidays abroad were associated with increased levels of vitamin D. Even when data were adjusted for these factors, the association was not completely removed - which suggests that factors other than sun exposure are involved, the researchers say. They highlight the need for further research into the genetic links between vitamin D levels and pigmentation.
Dr Adrian Martineau, a Clinical Research Fellow at Queen Mary, University of London who studies the role of vitamin D in tuberculosis infection, says of the 'PLoS One' paper: "The research by Glass and colleagues confirms and extends finding of Malvy et al. to a UK population.
"It will be very interesting to see the results of the genetic analysis that the authors propose - especially of polymorphisms [genetic variants] in D binding protein. Variants in this protein associate strongly with skin colour, and also with vitamin D status, so may end up being explanatory.
"It would definitely not be appropriate to advise women with pale skin to sunbathe more on the basis of this research."
In other work in this field, researchers at the Department of Twin Research have recently identified four genes associated with variation in vitamin D levels through a genome-wide study in collaboration with many other groups. The results of this work will be published soon.
Image: Catching sun. Credit: Impala74 on Flickr
References
Glass D et al. Pigmentation and vitamin D metabolism in Caucasians: low vitamin D serum levels in fair skin types in the UK. PLoS One 2009;4(8):e6477.
Malvy DJ et al. Relationship between vitamin D status and skin phototype in general adult population. Photochem Photobiol 2000;71(4):466-9.