Women who are overweight or obese are at greater risk of developing rheumatoid arthritis (RA), according to a new study presented at the 2012 annual meeting of the American College of Rheumatology. This adds to existing evidence that maintaining a healthy weight is necessary to avoid potential health problems, including RA.

“Controlling your weight not only prevents diabetes and cardiovascular diseases, but it can also prevent RA,” says study researcher Bing Lu, MD, assistant professor of medicine at Brigham and Women's Hospital in Boston.

“Previous studies have had inconsistent results, but we were able to confirm that obesity increases RA risk based on two large studies, with a much better study design and a very large sample size,” says Dr. Lu.

For the analysis, Dr. Lu and his colleagues reviewed two large studies, the Nurses’ Health Study (NHS), which ran from 1976 to 2008, and the Nurses’ Health Study II (NHSII), which ran from 1989 to 2009.

The NHS group included 121,700 female registered nurses, who were between the ages of 30 and 55 years at the start of the study; the NHSII group included 116,608 nurses between the ages of 25 and 42 years at the start of the study.

Their body fat was calculated by using the Body Mass Index (BMI), a ratio of weight to height. Women were classified as being of normal weight if their BMI was 25 or less, overweight if their BMI was between 25.0 to 29.9 and obese if their BMI was 30 or greater.