London: Eating oily fish reduces the risk of developing rheumatoid arthritis, but smoking and stress can hasten the advent of the condition, according to a new study.

New data presented June 13 at EULAR 2008, the Annual Congress of the European League Against Rheumatism in Paris, France, shows that intake of oily fish is associated with a reduced risk of developing rheumatoid arthritis (RA), whereas psycho-social work stress and smoking can increase the risk of developing the condition.

The findings of the study, by Swedish researchers, has also shed light on the important role of environmental and social factors in the development of rheumatoid arthritis, better known as RA.

The study, which involved 1,899 patients, found that the intake of oily fish reduced an individual's risk of developing RA by as much as 20 to 30 percent.

Researchers found that the odds ratio (OR) for developing RA was 0.8 for those who consumed oily fish one to seven times a week or one to three times a month, compared with those who never, or seldom consumed oily fish.

However, the study found no significant association with RA risk and the consumption of fish oil supplements.

The researchers found that there is a dose dependency for the level of smoking on the odds ratio of developing RA. The highest odds ratios were seen in those carrying a risk variant of a susceptibility gene called PTPN22.

The study also found psycho-social stress at work, defined as low decision latitude (or low level of control), was associated with a higher risk for RA.

"The findings from these studies add to an increasing body of evidence to support the assertion that lifestyle modifications can have a significant impact on an individual's risk for developing RA, one of the most common autoimmune diseases, affecting approximately one percent of adults worldwide," said Annmarie Wesley, the author of the study.

"We hope that the data will contribute to the growing understanding of the aetiology of RA and, ultimately, its treatment and prevention."