Vitamin D is made in our bodies by UV-B light from the sun.
Some studies have suggested a link between vitamin D deficiency and autoimmune diseases such as MS. This possible link might also explain the increasing prevalence of autoimmune disease among those living far from the equator, where there are lower levels of winter sun.
Autoimmune diseases – like MS and type 1 diabetes – are diseases where the immune system mistakenly attacks the bodys own tissues or harmless substances that enter the body.
University of Aberdeen researchers studied patients in the north of Scotland – which has the highest rate of MS in the UK – who were being treated during winter with artificial UV-B light therapy for skin diseases caused by their immune systems acting inappropriately.
Researchers looked at the impact of the UV-B light on vitamin D levels, as well as its impact on cells known as regulatory T cells, which play a critical role in the immune system, keeping it in balance and preventing it from carrying out damaging autoimmune responses.
Regulatory T cells are known to be lacking in some patients with autoimmune diseases. Previous research has also shown that regulatory T cell function is enhanced by vitamin D.
Dr Anthony Ormerod, Clinical Reader in Dermatology at the University, said: Our study shows that UV-B light, which mimics sunshine, can have a striking effect on the immune system of patients.
We found that UV-B light boosted the production of vitamin D, and of regulatory T cells, which play an important role keeping our immune systems in check.
Our findings have important implications for future interventions including the recommendations for healthy lifestyle and a possible role for phototherapy and / or vitamin D supplementation in the prevention or treatment of autoimmune and inflammatory diseases.
While too much exposure to sunlight is harmful and increases skin cancer risk, these results suggest that subjects in our study would have some benefits from small amounts equivalent to summer exposure in the winter but more work needs to determine the role of sunlight and the role of supplementing the diet with vitamin D.
Dr Helen Macdonald, senior lecturer in nutrition and translational musculoskeletal research at the University and Chair of the National Osteoporosis Society Nutrition and Lifestyle forum, said: There are risks associated with high levels of both therapies, so it is important that we get the balance right.
We would also want to stress that we are not advocating sun bed use since this is not the same type of radiation produced by sun beds which already have well-documented health risks.
The average dose of UV light that the volunteers received was the equivalent to sunlight exposure in Aberdeen over spring and summer and further work is required to determine if lower doses are effective.
Professor Mark Vickers, Chair in Applied Medicine at the University, said: Ours is the first study to demonstrate in patients a cause and effect between UV light, vitamin D and systemic immune function in people.
Professor Rob Barker, Chair in Medicine and Therapeutics at the University, added: Our study suggests a predisposition to autoimmune and allergic responses may be explained by a deficiency in exposure to sunlight, which in turn leads to a lack of vitamin D and regulatory T cells.
The study was conducted by University of Aberdeen medical student Sarah Milliken under the supervision of the researchers.