Air Pollution May Affect Risk of Rheumatoid Arthritis

November 15, 2011

By Fran Lowry

NEW YORK (Reuters Health) Nov 11 - Air pollution, especially sulfur dioxide, may increase the risk of rheumatoid arthritis (RA), Boston researchers said this week at the American College of Rheumatology Annual Scientific Meeting in Chicago.

"Some cardiovascular disease is associated with increased inflammatory markers and oxidative stress from air pollution, and respiratory exposures to silica and cigarettes are associated with rheumatoid arthritis, so it seemed logical to look at rheumatoid arthritis and links to air pollution because the disease is characterized by such a large level of inflammation," Dr. Jaime Hart told Reuters Health.

Collaborating with researchers from the Karolinska Institutet in Stockholm, Dr. Hart and colleagues from Harvard Medical School studied 1,330 incident RA cases and 2,235 controls. The data came from the Swedish Epidemiological Investigation of Rheumatoid Arthritis (EIRA) study and from the U.S. Nurses' Health Study (NHS).

The researchers created models that predicted exposures to common air pollutants in gas form, such as carbon monoxide, sulfur dioxide and nitrogen dioxide, or particulate air pollution, such as soot or dust at the participants' residential addresses.

They then examined the association between increases in these pollutants and the risk of developing RA, after controlling for age, gender, socioeconomic status, education, race, smoking, hormone use, physical activity, and body mass index.

They found no evidence of an increased risk of RA from particulate air pollution either in Sweden or in the U.S.

In the Swedish cohort, however, they did find that increasing exposure to gas air pollutants over 10 to 20 years was associated with an increased risk of developing RA.

For example, for each interquartile range increase in exposure, the risk of RA onset 10 years later rose by 7% with each interquartile range increase in exposure to sulfur dioxide, 11% for each interquartile range increase in nitrogen dioxide exposure, and 7% for each interquartile range increase in exposure to nitrogen oxide.

The risks were higher in people of lower socioeconomic status, Dr. Hart said.

"People of lower socioeconomic status are generally at lower baseline health so an additional insult to them from air pollution may be more harmful," she said. "Also they tend to live in poor neighborhoods, in older housing stock, and a greater proportion of the pollution may be getting into their house."

"We also found that home heating pollution in Sweden tended to be more adverse," she noted.

The results from this study need to be replicated in larger geographic areas and in more diverse populations, Dr. Hart added.

"Our study adds to the body of literature that air pollution is not good for you. Our hope is that it will stimulate more research looking into this disease."

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