Newswise — WASHINGTON – 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.
The American College of Rheumatology is an international professional medical society that represents more than 9,000 rheumatologists and rheumatology health professionals around the world. Its mission is to advance rheumatology. The ACR/ARHP Annual Meeting is the premier meeting in rheumatology. For more information about the meeting, visit www.acrannualmeeting.org or join the conversation on Twitter by using the official hashtag: #ACR2012.
Learn more about living well with rheumatic disease as well as rheumatologists and the role they play in health care. Also, discover the ACR’s Simple Tasks campaign, which highlights the severity of rheumatic diseases and the importance of early and appropriate referral to a rheumatologist.
Editor’s Notes: Bing Lu, MD, DrPH will present this research during the ACR Annual Meeting at the Walter E. Washington Convention Center at 3:30 PM on Monday, November 12. Dr. Lu will be available for media questions and briefing at 1:30 PM on Tuesday, November 13 in the on-site press conference room, Room 203 A-B.
Presentation Number: 1608
Overweight and Obesity Increase Risk of Rheumatoid Arthritis in Women in a Large Prospective Study
Bing Lu (Brigham and Women’s Hospital, Harvard Medical School, Boston, Mass.)
Chia-Yen Chen (Harvard School of Public Health, Boston, Mass.)
Linda T. Hiraki (Brigham and Women's Hospital, Harvard School of Public Health, Boston, Mass.)
Karen H. Costenbader (Brigham and Women's Hospital, Harvard Medical School, Boston, Mass.)
Elizabeth W. Karlson (Brigham and Women's Hospital, Harvard Medical School, Boston, Mass.)
Background/Purpose: Several case-control studies have suggested that overweight and obesity may increase the risk of rheumatoid arthritis (RA), but the evidence is conflicting. We examined the relationship between pre-existing overweight or obesity in development of future RA in two large prospective cohorts, the Nurses' Health Study (NHS) and Nurses' Health Study II (NHSII).
Methods: The NHS is a prospective cohort study established in 1976 that enrolled 121,700 US female registered nurses, ages 30–55 years. NHSII began in 1989, enrolling 116,608 female nurses aged 25–42 years. Lifestyle and environmental exposures and anthropometric measures have been collected through biennial questionnaires. The incident RA cases were identified using the previously validated connective tissue disease screening questionnaire followed by a medical record review, according to the 1987 ACR criteria. Body Mass Index (BMI) was calculated as weight /height 2 (kg/m2). Overweight and obesity were defined as 25.0≤BMI<30 kg/m2 and BMI≥30.0 kg/m2 respectively based on World Health Organization classification. We assessed the exposure variable using a time-varying status of overweight and obesity since baseline updated every two years up to 2006/2007. Cox proportional hazards models were used to estimate hazard ratios (HR) of RA, seropositive RA, and seronegative RA phenotypes after adjusting for potential confounders.
Results: During 2,769,593 person-years of follow-up from 1976 to 2008 in NHS and 2,139,702 person-years of follow-up from 1989 to 2009 in NHSII, 1292 incident cases of RA developed (903 in NHS, 389 in NHSII). The age-adjusted incidence rates of RA ranged from 30 to 36 /100,000 person-years in NHS, and 12 to 26 /100,000 person-years in NHSII across increasing levels of BMI. Overweight and obese women have increased risk of RA compared with women with BMI<25 (Table). The multivariate hazard ratios of RA in NHS were 1.19 (95% CI, 1.03-1.38) for overweight and 1.18 (95% CI, 0.98-1.42) for obesity respectively (p trend = 0.029). Consistent with the NHS, the HRs in NHSII were 1.78 (95% CI, 1.40-2.26) for overweight, and 1.73 (95% CI, 1.34-2.23) for obesity (p trend <0.001). Further stratified analyses in NHS demonstrated that the effect of overweight and obesity on RA risk was stronger in seronegative RA than in seropositive RA. The multivariate HRs of seronegative RA were 1.30 (95% CI, 1.03-1.63) for overweight and 1.34 (95% CI, 1.01-1.77) for obese, while the HRs of seropositive RA were 1.12 (95% CI, 0.92-1.36) for overweight and 1.08 (95% CI, 0.84-1.38).
Conclusion: In this long-term prospective cohort study of women, we found overweight and obesity were significantly associated with increased risk of developing future RA compared to women with BMI <25kg/m2. Future studies are needed to confirm our findings in other populations.
Disclosure: B. Lu, None; C. Y. Chen, None; L. T. Hiraki, None; K. H. Costenbader, None; E. W. Karlson, None.