London: Soaking up the Sun may reduce women`s risk of developing rheumatoid arthritis, according to a new study.
Researchers found that women regularly exposed to sunlight reduced their risk of developing the condition by a fifth.
However, using sun creams or covering up to avoid the rays could lessen the protective effects.
Rheumatoid arthritis is an autoimmune disease that causes inflammation in joints and the main symptoms are joint pain and swelling.
The long term study looked at participants in two phases of the US Nurses` Health Study, the first of which has tracked the health of more than 120,000 nurses since 1976, when they were aged between 30 and 55, until 2008, the `Daily Mail` reported.
The second phase tracked the health of a further 115,500 nurses since 1989, when they were aged between 25 and 42, until 2009.
Rather than simply relying on geography to quantify likely levels of UVB exposure, the researchers used a more sensitive assessment, known as UV-B flux, which is a composite measure of UVB radiation, based on latitude, altitude, and cloud cover.
Exposure was then estimated according to where they lived in the US and ranged from an annual average of 93 in Alaska and Oregon to 196 in Hawaii and Arizona where they get the most sunshine.
Likely estimates of UV exposure at birth and by the age of 15 were also included.
Over the period, 1,314 women developed rheumatoid arthritis.
Among nurses in the first phase, higher cumulative exposure to UVB was associated with a reduced risk of developing the disease.
Those with the highest levels of exposure were a fifth less likely to develop rheumatoid arthritis than those with the least.
This confirms the findings of other studies, showing a link between geography and the risk of rheumatoid arthritis as well as other autoimmune conditions, including type 1 diabetes, inflammatory bowel disease, and multiple sclerosis.
But no such association for UV-B exposure was found among women in the second phase because these women were younger than those in the first study, and so might have been more aware about the potential hazards of acquiring a tan.
"Our study adds to the growing evidence that exposure to UV-B light is associated with decreased risk of rheumatoid arthritis. The mechanisms are not yet understood, but could be mediated by the cutaneous production of vitamin D and attenuated by use of sunscreen or sun avoidant behaviour," researchers said.
The study was published in the Annals of the Rheumatic Diseases.