Some research has suggested a connection between exposure to air pollution and the risk of developing rheumatoid arthritis, but a large study of US nurses has found no link.
Nearly 1pc of US adults have rheumatoid arthritis, an incurable joint-eroding disease that deforms patients' bodies, triples their risk of heart attack and raises their chances for certain cancers.
"Overall, we did not observe any evidence that increases in pollution levels were associated with increases in the risk of rheumatoid arthritis," wrote study leader Jaime Hart, an instructor of medicine at Brigham and Women's Hospital in Boston, in an email.
The triggers for the inflammation at the root of rheumatoid arthritis still elude researchers.
Some have theorised that pollution could set off an inflammatory response in the lungs that would then spread to the entire body. Genetic risk factors, interacting with the environment or hormones, are also thought to play a role because women tend to get the disease more than men.
For the study, Hart's group used data from the Nurses' Health Study, a registry that tracked 111,425 women – all originally registered nurses – across the United States every two years from 1976 to 2006.
Over three decades, 858 confirmed cases of rheumatoid arthritis arose among the women, according to the report.