Being overweight is linked to a higher risk of rheumatoid arthritis in women, according to new research findings presented this week at the American College of Rheumatology Annual Meeting in Washington, D.C.

Rheumatoid arthritis is a chronic disease that causes pain, stiffness, swelling, limitation of motion and loss of function of multiple joints. Though joints are the principal areas affected by RA, inflammation can develop in other organs as well. An estimated 1.3 million Americans have RA, and the disease typically affects women twice as often as men.

While several case-control studies have suggested a link between excess weight and RA risk, evidence was conflicting. So researchers at Brigham and Women's Hospital, Harvard Medical School and Harvard School of Public Health decided to investigate further to confirm and better understand the connection. "Obesity or being overweight is a major global public health problem," says Bing Lu, MD, DrPH, researcher at Brigham and Women's Hospital in Boston, and the lead investigator in the study. He and his colleagues sought to learn more about the connections between excess weight in women and RA through this study.

The researchers looked at the relationship between pre-existing overweight and obesity conditions and future risk of developing RA in women. Data was gathered from two large cohort studies, the Nurses Health Study and Nurses Health Study II. In the first study, 121,700 females of ages 30 to 55 were included. In the second study, 116,608 females of ages 25 to 42 were included.

All participants answered questionnaires to determine lifestyle and environmental exposures as well as body mass index (commonly called BMI). A person with a BMI of 25 to 29.9 is considered overweight. A person with a BMI of 30 or higher is considered obese. RA was determined based on connective tissue screening questionnaires and review of medical records. The analysis was adjusted for factors such as age, tobacco and alcohol use, breastfeeding, oral contraceptive use, menopausal status and post-menopausal hormone use, etc.

Results showed that women who were overweight or obese had a higher incidence of developing future RA compared to women with normal weight. Hazard ratio is a statistical term to describe a ratio of the incident rates at which the study participants in the groups are developing RA. Women who were overweight with BMIs of 25 to 29.9, had a hazard ratio of 1.19 in the first cohort and 1.78 in the second cohort (meaning a 19 percent and 78 percent increased risk of developing RA, respectively). Women who were obese, with a Body Mass Index higher than 30, had hazard ratios of 1.18 and 1.73 in the two cohorts respectively.

"This study examining the potential role of obesity and overweight in [the] development of RA may furnish novel information about the etiology of RA, and have large potential public health implications," Dr. Lu says.

Funding for this study was provided by the National Institutes of Health.