According to new research led by Professor Elizabeth Arkema and colleagues from Harvard, increased sun exposure may cut the risk of developing rheumatoid arthritis.
The study, recently published in JAMA, found that more intense sun exposure was linked with a decreased incidence of rheumatoid arthritis (RA) among women in the Nurses’ Health Study (NHS).
The NHS established a large cohort in 1976 of over one-hundred thousand nurses to follow over time. In this recent analysis, the researchers found that 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. Conclusive evidence? Not so fast.
In 1989, the NHSII was established; a second and different cohort of over 115,000 women. In this cohort, the researchers found no such decreased risk associated with sun exposure.
The risk over 20 years for RA was 0.7% among women in NHS living in states with the highest UVB compared with 1.2% in those living in states with lowest levels. There was no difference in risk between highest and lowest UVB exposure in NHSII.
They provide a possible explanation,
“The later birth cohort of NHSII participants (born between 1946 and 1964) were more likely aware of the dangers of sun exposure and, perhaps, had more sun-protective behavior, making residential UVB not as good a proxy for actual sun exposure in NHSII.”
They conclude that the current findings strengthen evidence that more intense sun exposure lowers the risk of RA.
“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,” they explain.
The authors call for further research to examine the most effective UVB intensity and timing of exposure.