A moderate dose of ultraviolet light during the winter months increases the levels of vitamin D in the blood and appears to put a brake on the T-cell arm of the immune system--which could reduce the severity of autoimmune disease, a new small-scale study on a group of Scottish patients has shown.
The research was led by Mark Vickers and Anthony Ormerod, a professor and clinical reader in dermatology, respectively, at the University of Aberdeen. It was reported in the Journal of Allergy and Clinical Immunology.
The trial was conducted between December and March, 2012. Before and after exposing 24 subjects repeatedly to the equivalent of a quarter of a day's worth of summer sunlight, the scientists measured blood levels of vitamin D; the fraction of white blood cells comprised of "regulatory" T cells; and the degree to which T cells expanded their numbers when stimulated.
Regulatory T cells are a subset of T cells known to suppress the activity of other T cells. According to Wikipedia, "Mouse models have suggested that modulation of Tregs can treat autoimmune disease and cancer, and facilitate organ transplantation." Eczema with an allergic component qualifies as an autoimmune disease.
The scientists found that, after two weeks' exposure to UV, vitamin D levels increased by 50%; after four weeks, by 100%. The fraction of regulatory T cells increased threefold, and other classes of T cells reacted less vigorously to stimulation.
While I am always interested in the connection between vitamin D, T cells, and eczema--I wonder whether this study really tells us anything new. The American Academy of Dermatology says there is no safe recommended level of exposure to UV (because of the risk of skin cancer).
The connection between vitamin D and regulatory T cells appears to be well-established, according to a PubMed search I just did. And everyone knows that regulatory T cells suppress other T cells.
Having spent several years in the north of Scotland myself, I well know how little sunlight the Scots get in the winter. Were the subjects' vitamin D levels low to begin with? I bet they were. Could they benefit from supplements? Almost certainly.
Especially since, as I recall, the Scottish diet consists largely of chips, lager, and cigarettes!