(HealthDay News) – In a cohort of older women, exposure to ultraviolet-B (UV-B) light is associated with a significantly reduced risk of rheumatoid arthritis (RA), but this relationship is not seen among younger women, according to research published online Feb. 4 in the Annals of the Rheumatic Diseases.
To examine the correlation between exposure to UV-B light and the risk of RA, Elizabeth V. Arkema, PhD, of the Harvard School of Public Health in Boston, and colleagues used data from the Nurses’ Health Study (NHS) and NHSII involving 106,368 women (aged 30–55 years in 1976) and 115,561 women (aged 25–42 years in 1989), respectively. The women were followed until 2008 and 2009, respectively.
The researchers identified 1,314 incident cases of RA. Higher cumulative average UV-B exposure correlated with decreased risk among NHS participants (highest versus lowest category hazard ratio, 0.79). In women from NHS II there was no correlation between UV-B exposure and RA risk (hazard ratio, 1.12; 95% confidence interval, 0.87–1.44). The results were similar for exposure to UV-B at birth and at age 15.
“In conclusion, our study adds to the growing evidence that exposure to UV-B light is associated with decreased risk of RA,” the authors write. “The mechanisms are not yet understood, but could be mediated by cutaneous production of vitamin D and attenuated by use of sunscreen or sun avoidant behavior.”