People who live near major roads and interstates and the traffic pollution they generate may have a greater risk of developing rheumatoid arthritis.

That’s the conclusion of a new study that compared the medical records of more than 90,000 participants in the Nurses Health Study with the proximity of their homes to busy roadways.

Researchers found that women who lived within 50 meters, or 164 feet, of interstates or primary, multi-lane roads had a 63 percent increased risk of developing rheumatoid arthritis compared with women who lived more than 200 meters, or about one-tenth of a mile, away from major thoroughfares.

The study was published in the March 2009 online edition of Environmental Health Perspectives, the journal of the National Institute of Environmental Health Sciences.

Previous research has indicated that environmental factors may play a risk in the development of rheumatoid arthritis, including exposure to cigarette smoke, and occupational exposures to mineral oil and silica. And other research has demonstrated that air pollution from traffic, much like cigarette smoke, can cause systemic inflammation, a hallmark of the disease.

For the current study, researchers at Brigham and Women’s Hospital, in Boston, and at the University of South Carolina in Columbia, combed the health records of more than 90,000 women enrolled in the Nurses Health Study to identify women diagnosed with rheumatoid arthritis.

They then used computer-mapping technology to measure the distance of all the nurses’ homes from major roads.

Those who lived within 50 meters of major streets (usually larger than two lanes), primary multi-lane roads, or interstates, had a 31 percent elevated risk of developing rheumatoid arthritis compared to women who lived 200 or more meters away. The risk remained elevated even after researchers eliminated the effects of things like age, race, sex, socioeconomic status and cigarette smoking. When researchers restricted their analysis to nurses who lived within 50 meters of the largest roadways, the risk of developing rheumatoid arthritis rose from 31 to 63 percent.

Elizabeth W. Karlson, MD, a rheumatologist at Brigham and Women’s Hospital and Harvard Medical School, co-authored the study.

She says the findings fit well with previous research conducted by her group which found that those living in the Midwest and Northeast, areas with higher levels of air pollution, have significantly higher risks of developing rheumatoid arthritis than those living in the West.

“The hypothesis is that living close to the road exposes women to more traffic, which is a major source of air pollution, and that increases their risk,” Dr. Karlson says.

Of concern, Dr. Karlson says, are particulates, tiny bits of soot or dust mixed with droplets of acids or organic chemicals.

The smallest particulates pass through the nose and mouth and enter the lungs, where they can trigger an immune reaction.

“We’re interested in whether those particles from the traffic are responsible for this increased risk, or whether there’s some other pollutant,” she says.

Dr. Karlson notes, however, that the researchers were not able to measure actual pollution levels that the nurses may have been exposed to, nor were they able to gauge traffic intensity.

“The findings will need to be replicated by other research studies,” Dr. Karlson says.