Rheumatoid arthritis (RA) occurs most commonly in women, and is an intensely painful condition where your body’s own immune system attacks the joints. The reason why this happens is unknown, but this new study, published in the journal Annals of the Rheumatic Diseases, suggested a link between sunlight and the risk of developing the disease.
For the study, Harvard Medical School researchers monitored two groups of over 100,000 women, one from 1976 onwards, and the other from 1989. Based on where they lived, the participants’ estimated levels of UV-B radiation exposure were compared to their health, and the researchers found that, in the 1976 group, those who lived in the sunniest parts of the US were 21% less likely to develop RA than those who got the least UV radiation. Yet there was no link between UV levels and RA risk in the 1989 group.
According to the authors of the report, ‘our study adds to the growing evidence that exposure to UV-B light is associated with decreased risk of rheumatoid arthritis.’ They surmised that vitamin D, which is produced in sunlight, may be the reason why RA risk was reduced for the women in 1976, but that ‘differences in sun protective behaviour, e.g. greater use of sun block’ could explain why the younger group of women showed no benefit from living in sunnier climes.
A vitamin D deficiency has already been implicated by other immune system disorders, such as multiple sclerosis, but experts warn that this doesn’t mean you should spend all day in the sun. According to Dr Chris Deighton, the president of the British Society for Rheumatology, the study ‘gives us more clues’ about how the environment can affect your chances of developing RA, but ‘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.’
Professor Alan Silman, medical director of Arthritis Research UK, added, ‘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.’ He went on to say that ‘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.’