Rheumatoid arthritis: More common in sun-deficient women

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Dr. Elisabeth Arkema published the following study:

Arkema EV, Hart JE, Bertrand KA, Laden F, Grodstein F, Rosner BA, Karlson EW, Costenbader KH. 
Exposure to ultraviolet-B and risk of developing rheumatoid arthritis among women
in the Nurses' Health Study. Ann Rheum Dis. 2013 Apr;72(4):506-11.

OBJECTIVE: To examine the association between ultraviolet-B (UV-B) light exposure
and rheumatoid arthritis (RA) risk among women in two large prospective cohort
studies, the Nurses' Health Study (NHS) and the Nurses' Health Study II (NHSII).
METHODS: A total of 106 368 women from NHS, aged 30-55 years in 1976, and 115 561
women from NHSII, aged 25-42 in 1989, were included in the analysis. We
identified women with incident RA from the start of each cohort until 2008 (NHS) 
and 2009 (NHSII). Cumulative average UV-B flux, a composite measure of ambient UV
exposure based on latitude, altitude and cloud cover, was estimated according to 
state of residence and categorised as low, medium or high. Estimates of UV-B at
birth and age 15 years were also examined. We used multivariable-adjusted Cox
proportional hazards models to estimate HR and 95% CI.
RESULTS: 1314 incident RA cases were identified in total. Among NHS participants,
higher cumulative average UV-B exposure was associated with decreased RA risk;
those in the highest versus lowest category had a 21% decreased RA risk (HR (95% 
CI); 0.79 (0.66 to 0.94)). UV-B was not associated with RA risk among younger
women in NHSII (1.12 (0.87 to 1.44)). Results were similar for UV-B at birth and 
at age 15.
CONCLUSIONS: 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
From Karolinska Hospital where currently working Dr. Arkema explains the results

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