UVB rays may cut rheumatoid arthritis risk

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SOAKING up the sun may reduce a woman’s risk of rheumatoid arthritis, a study has shown.

Over-exposure to the sun’s ultraviolet (UV) rays can damage the skin and trigger skin cancer. But new research involving more than 200,000 women suggests sunshine can also cut the risk of rheumatoid arthritis (RA) by more than a fifth.

The findings are based on data from the Nurses’ Health Study, a major US investigation looking at lifestyle factors affecting women’s health.

Scientists looked at conditions where the women lived to work out their likely exposure to UVB rays.

The researchers used a sensitive measurement method known as UVB flux, which takes into account latitude, altitude and cloud cover.

It is expressed in R-B units, which relate to the impact of exposure over time. A count of 440 R-B units in 30 minutes, for example, would produce slight redness in untanned white skin.

Study participants from US states with different climates had different R-B ratings, the ­research – published in the journal Annals of the Rheumatic Diseases – found. Exposure ranged from an annual average of 93 R-B units in the northern states of Alaska and Oregon, to 196 in Hawaii and Arizona.

During the study period, which lasted up to three decades, a total of 1,314 women developed RA, an auto-immune condition that attacks the joints. Those with the highest levels of UVB exposure were 21 per cent less likely to develop the disease than those with the lowest.

The scientists, led by Dr Elizabeth Arkema, from the Harvard School of Public Health in Boston, wrote: “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 [skin] production of vitamin D and ­attenuated by use of sunscreen or sun-avoidant behaviour.”