A new study has shown that getting out in the sun may reduce the risk of rheumatoid arthritis (RA) in women. More intense sunlight exposure can damage the skin and may even trigger skin cancer. But it was also linked with a decreased incidence of RA among women by more than a fifth.
These findings are based on data from the Nurses’ Health Study, a major US investigation looking at lifestyle factors affecting women’s health.
Researchers looked at conditions where the women lived to work out their likely exposure to UV-B rays. They used a sensitive measurement method known as UV-B flux which takes into account latitude, altitude and cloud cover.
The study demonstrated immunosuppressive effects of UV-B, which also increases vitamin D synthesis in the skin that in turn, has immunomodulatory properties. Elizabeth V Arkema, from Harvard School of Public Health Massachusetts, and colleagues analyzed cumulative UVB flux data for 106,368 women enrolled in the Nurses’ Health Study and 115,561 women in the subsequent Nurses’ Health Study II according to the state in which they lived. In NHS, which began in 1976, 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 levels. But in NHSII, initiated in 1989 in women ages 25 to 42, no significantly lower risk was seen. According to study authors, 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 like using sun block in younger generations may explain the disparate results.
Based on previous studies, people living in northern latitudes, where the sun is less intense, have a higher risk of RA and other auto-immune conditions including multiple sclerosis, Type 1 diabetes, and inflammatory bowel disease.
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