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Posted on Feb 21, 2013, 6 a.m.
Exposure to sunlight associates with a decreased incidence of rheumatoid arthritis, among women.
Previously, some epidemiologic studies have found a correlation between an increased incidence of RA and other autoimmune diseases with higher latitude of residence. As well, experimental studies have demonstrated immunosuppressive effects of UV-B, which also increases vitamin D synthesis in the skin, that in turn, has immunomodulatory properties. Elizabeth V Arkema, from Harvard School of Public Health (Massachusetts USA), and colleagues analyzed cumulative UVB flux data for 106,368 women enrolled in the Nurses’ Health Study and 115,561 women in the subsequent Nurses’ Health Study II according to the state in which they lived. In NHS, which began in 1976, women (ages 30 to 55) living in states with the highest ultraviolet B (UVB) intensity had a 21% lower risk for RA compared with those living in states with low UVB levels. But in NHSII, initiated in 1989 in women ages 25 to 42, no significantly lower risk was seen. The study authors report that: "These results suggest that ambient UV-B exposure is associated with a lower RA risk in NHS, but not NHSII. Differences in sun-protective behaviours (eg, greater use of sun block in younger generations) may explain the disparate results."
Elizabeth V Arkema, Jaime E Hart, Kimberly A Bertrand, Francine Laden, Francine Grodstein, et al. “Extended report: Exposure to ultraviolet-B and risk of developing rheumatoid arthritis among women in the Nurses’ Health Study.” Ann Rheum Dis., 4 February 2013.
