More Sun May Lower Risk of RA

Rheumatoid arthritis risk may decrease with exposure to UVB sunlight

(RxWiki News) It's still unclear what exactly causes rheumatoid arthritis. As such, it's not entirely clear what steps people can take to prevent the condition. But new research suggests that soaking up the sun may help.

Researchers studied the relationship between exposure to sunlight - specifically the ultraviolet B (UVB) radiation in sunlight - and the risk of rheumatoid arthritis in two groups of women. The first group was older than the second group.

Results showed that regular exposure to UVB light may lower the risk of developing rheumatoid arthritis. However, this protective power of sunlight was only found in the older group of women.

According to the authors, there may have been no link between UVB exposure and rheumatoid arthritis among younger women because these women may be more aware of the risks of sunbathing and more likely to use sunscreen.

"Get some sun, but don't overdo it!"

The study was conducted by Elizabeth V. Arkema, MD, of Harvard School of Public Health and Brigham and Women's Hospital in Boston, and colleagues. 

The research involved two groups of women, one from the Nurses' Health Study (NHS) and one from the Nurses' Health Study II (NHSII). The NHS group included 106,368 women aged 30 to 55 years in 1976 who were followed until 2008. The NHSII group included 115,561 women aged 25 to 42 years in 1989 who were followed until 2009.

A total of 1,314 women developed rheumatoid arthritis. 

The researchers used more than geographic location to measure exposure to UVB light. Participants' UVB exposure was determined using UVB flux - a combined measure of UVB radiation based on latitude, altitude and cloud cover.

Among women in the NHS group, higher exposure to UVB was associated with a lower risk of rheumatoid arthritis. Results showed that NHS participants with the highest UVB exposure had a 21 percent lower risk of rheumatoid arthritis than those with the lowest exposure.

In contrast, there was no association between UVB exposure and rheumatoid arthritis risk among the younger women in NHSII.

The authors explained that these differences may be the result of different attitudes about sun exposure. "Differences in sun-protective behaviors (e.g., greater use of sunblock in younger generations) may explain the disparate results," they said.

The authors also noted that it's not clear at what point in a person's life UVB protects most against rheumatoid arthritis.

"Our study adds to the growing evidence that exposure to UVB light is associated with decreased risk of rheumatoid arthritis. The mechanisms are not yet understood, but could be mediated by the cutaneous (relating to the skin) production of vitamin D and attenuated by use of sunscreen or sun avoidant behavior," they concluded.

The study was published February 4 in the Annals of the Rheumatic Diseases. Funding and disclosure information was not available.

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Review Date: 
February 6, 2013