Excess Weight Linked to Increased Risk of Developing Rheumatoid Arthritis

Overweight women face a higher risk of rheumatoid arthritis than their normal-weight peers, according to a study presented at the annual scientific meeting of the American College of Rheumatology in Washington, DC.

Women from two prospective cohorts who were overweight with body mass indexes of 25 to 29.9 were 19 percent more likely or 78 percent more likely to develop RA than women whose BMI was less than 25 kg/m². Those who were obese, with BMI over 30 were 18 percent and 73 percent more likely to develop RA than their normal weight counterparts.

“We found that being overweight or obese increased the chance that women will get RA,” said lead investigator Bing Lu, MD, DrPH, assistant professor of medicine at Brigham and Women’s Hospital and assistant professor of medicine at Harvard Medical School. “We also found that the effect was stronger in seronegative type of RA.” In contrast, women whose weight remained level didn’t have a higher risk. He noted that the two different phenotypes may be due to different genetic and environmental studies.

While he couldn’t definitively explain the findings, Lu speculated that inflammatory proteins known as cytokines regulate the immune system. Given that rheumatoid arthritis is an inflammatory disease, it’s possible that obesity increases risk of RA.

This long-term prospective cohort study builds upon earlier studies, which were case control studies, limited by causality bias. According to Lu, the his research team’s ability to measure obesity before onset of RA, the large sample size and long follow-up time yielded more reliable results than the earlier studies which were inconclusive.

Researchers at Brigham and Women’s Hospital, Harvard Medical School and Harvard School of Public Health decided to examine the relationship between women who were overweight and obese and their future risk of developing RA. They drew upon data from more than 230,000 women from two large, prospective cohort studies, the Nurses Health Study and Nurses Health Study II, which followed women for up to 32 years and involved 1292 cases of RA.

Data came from questionnaires that captured lifestyle and environmental information, as well as body mass index. Women with a BMI of 25 to 29.9 were considered overweight. Those with a BMI of 30 or higher were considered obese. Rheumatoid arthritis was validated based on connective tissue screening questionnaires and a review of medical records. The researchers adjusted for factors such as age, tobacco and alcohol use, breastfeeding, use of oral contracepties, menopausal status and post-menopausal hormone use.

The study design allowed the researchers to examine the association of risk factors measured before onset of RA, which reduced some chance of bias.

When asked about the takeaway message of the study, Lu noted that besides preventing cardiovascular disease and diabetes, “controlling weight will also reduce risk of rheumatoid arthritis.”

Future studies are needed, the researchers noted, to confirm these findings in other populations.

The National Institutes of Health provided funding for this study.