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UVB exposure associated with lower RA risk for older women
Exposure to ultraviolet-B sunlight was associated with a lower risk for rheumatoid arthritis among older women compared with younger women, according to study results.
Researchers evaluated 106,368 women from the Nurses’ Health Study (NHS), a prospective study of nurses aged 30 to 55 years living in 11 US states in 1976, and 115,561 women from the Nurses’ Health Study II (NHSII), a cohort aged 25 to 42 years residing in 14 states in 1989. Incident rheumatoid arthritis (RA) was identified in each cohort: from 1976 to 2008 for NHS and from 1989 to 2009 for NHSII. Women with prevalent RA at baseline were excluded.
Elizabeth V. Arkema
State of residence was used to estimate a composite measure of ambient ultraviolet (UV) exposure based on latitude, altitude and cloud cover, called cumulative average UVB flux. It was categorized as low, medium or high. Researchers also examined estimates of UVB at birth and at age 15 years.
Researchers identified 1,314 cases of RA, 933 in NHS (mean age at diagnosis, 58.7 years) and 381 in NHSII (mean age at diagnosis, 47 years). Decreased RA risk was associated with higher cumulative average UVB exposure in the NHS cohort, in which women in the highest exposure category had a 21% decreased risk for RA (HR=0.79; 95% CI, 0.66-0.94) compared with women in the lowest category. In the NHSII cohort, UVB exposure was not associated with RA risk (HR=1.12; 95% CI, 0.87-1.44). Both cohorts had similar results for UVB at birth and at age 15.
“Regular exposure to sunlight — specifically ultraviolet B — may reduce the risk of developing rheumatoid arthritis,” researcher Elizabeth V. Arkema, ScD, ScM, of the Division of Rheumatology, Immunology and Allergy, Brigham and Women’s Hospital and Harvard Medical School, told Healio.com. “We observed that a higher average UVB exposure was associated with a 21% decreased risk of rheumatoid arthritis in an older group of women. We did not find an association in the younger cohort of women (born after 1946), which we speculate may be to differing sun-avoidant behaviors.”