5 February 2013 Last updated at 02:34 GMT
Sunshine may 'reduce arthritis risk'
Living in a sunnier climate may reduce the risk of developing rheumatoid arthritis, according to US researchers.
Their study of more than 200,000 women, published in the journal Annals of the Rheumatic Diseases, suggested a link between sunlight and the risk of developing the disease.
They speculated that vitamin D, which is produced in sunlight, may protect the body.
Experts warned that people should not spend all day in the sun.
Rheumatoid arthritis is caused by the body's own immune system attacking the joints and it can be intensely painful.
It is more common in women, but the reason why a patient's own defences turn against them is unknown.
Researchers at Harvard Medical School followed two groups of more than 100,000 women. The first were monitored from 1976 onwards, the second from 1989.
Their health was then compared with estimates of the levels of UV-B radiation they were exposed to, based on where they lived.
In the 1976 group, those in the sunniest parts of the US getting the highest levels of sunshine were 21% less likely to develop rheumatoid arthritis than those getting the least UV radiation.
However, UV levels had no affect upon the risk of rheumatoid arthritis is the 1989 group.
The report's authors said: "Our study adds to the growing evidence that exposure to UV-B light is associated with decreased risk of rheumatoid arthritis."
They suggested that "differences in sun protective behaviours, eg greater use of sun block" could explain why the younger group of women showed no benefit from living in sunnier climes.
One theory is that difference in levels of vitamin D, which is produced when UV radiation hits the skin, could affect the odds of developing the disease. Low levels of vitamin D have already been implicated other immune system disorders such as multiple sclerosis.
Dr Chris Deighton, the president of the British Society for Rheumatology, said it was an "interesting study" which "gives us more clues" about how the environment can affect the chances of getting rheumatoid arthritis.
He added: "We cannot advocate everybody sitting in the sunshine all day to protect from rheumatoid arthritis, because UV-B burns people and increases the risk of skin cancer.
"The treatment options in rheumatology have transformed the lives of patients with this crippling disease in recent years and anything that adds to our knowledge is welcomed."
Prof Alan Silman, medical director of Arthritis Research UK, said: "Studies that have been undertaken have not shown, thus far, that vitamin D is a useful treatment for rheumatoid arthritis.
"We know that many people with arthritis have low levels of vitamin D and this can have a powerful effect on the types of immune cells which may cause this condition.
"We're currently doing research to find out how this happens and are performing lab studies to find out whether vitamin D can alter the aggressive immune response found in rheumatoid arthritis and turn it into a less harmful or even a protective one.
"In the meantime, until we know more, the best thing that people can do is to go out in the sunshine for up to 15 minutes in the summer months and expose their face and arms to the sun to top up their vitamin D levels."
Ann Rheum Dis doi:10.1136/annrheumdis-2012-202302
Clinical and epidemiological research
Exposure to ultraviolet-B and risk of developing rheumatoid arthritis among women in the Nurses’ Health Study
Elizabeth V Arkema1,2, Jaime E Hart3,4, Kimberly A Bertrand1,3, Francine Laden1,3,4, Francine Grodstein1,3, Bernard A Rosner3,5, Elizabeth W Karlson2, Karen H Costenbader2
+ Author Affiliations
1Department of Epidemiology, Harvard School of Public Health, Boston, Massachusetts, USA
2Division of Rheumatology, Immunology and Allergy, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts, USA
3Channing Division of Network Medicine, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts, USA
4Department of Environmental Health, Harvard School of Public Health, Boston, Massachusetts, USA
5Department of Biostatistics, Harvard School of Public Health, Boston, Massachusetts, USA
Dr Elizabeth V Arkema, Department of Epidemiology, Harvard School of Public Health, 677 Huntington Avenue, 9th Floor, Boston, MA 02115, USA; email@example.com
Received 4 July 2013
Revised 3 January 2013
Accepted 4 January 2013
Published Online First 4 February 2013
Objective To examine the association between ultraviolet-B (UV-B) light exposure and rheumatoid arthritis (RA) risk among women in two large prospective cohort studies, the Nurses’ Health Study (NHS) and the Nurses’ Health Study II (NHSII).
Methods A total of 106?368 women from NHS, aged 30?55?years in 1976, and 115?561 women from NHSII, aged 25?42 in 1989, were included in the analysis. We identified women with incident RA from the start of each cohort until 2008 (NHS) and 2009 (NHSII). Cumulative average UV-B flux, a composite measure of ambient UV exposure based on latitude, altitude and cloud cover, was estimated according to state of residence and categorised as low, medium or high. Estimates of UV-B at birth and age 15 years were also examined. We used multivariable-adjusted Cox proportional hazards models to estimate HR and 95% CI.
Results 1314 incident RA cases were identified in total. Among NHS participants, higher cumulative average UV-B exposure was associated with decreased RA risk; those in the highest versus lowest category had a 21% decreased RA risk (HR (95% CI); 0.79 (0.66 to 0.94)). UV-B was not associated with RA risk among younger women in NHSII (1.12 (0.87 to 1.44)). Results were similar for UV-B at birth and at age 15.
Conclusions 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 (eg, greater use of sun block in younger generations) may explain the disparate results.
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