Background In a previous study from the United States (1), obesity has been associated with increasing incidence of rheumatoid arthritis (RA) in women. In a small study of autoantibody positive individuals at risk for RA from the Netherlands, overweight was a risk factor for RA development (2). The underlying mechanisms are incompletely understood.
Objectives To examine sex-specific effects of body mass index (BMI) on the future risk of RA.
Methods Between 1974 and 1992, subjects (n=33346; 22444 men and 10902 women) from a defined catchment area were included in a Preventive Medicine Program (PMP). Information on life style factors was obtained using a self-administered questionnaire. Height and weight were measured in light indoor clothing as part of the health survey. Classification of socio-economic status was based on information on occupation derived from the National Census, and collapsed into two predefined categories, white-collar workers and blue-collar workers. From this population, we identified individuals who developed RA after inclusion by linking the PMP register to the local community based RA register, the local patient administrative register, the National Hospital Discharge Register and the National Cause of Death Register. In a structured review of the medical records, patients were classified according to the 1987 American College of Rheumatology criteria for RA, and the year of RA diagnosis was noted. Four controls for every validated case, matched for sex, year of birth and year of screening, who were alive and free of RA when the index person was diagnosed with RA, were selected from the PMP register. The impact of BMI on the risk of RA was examined in conditional logistic regression models, stratified by sex
Results Two hundred and ninety patients (151 men and 139 women) were diagnosed with RA and fulfilled the ACR criteria after inclusion in the PMP. The median time from inclusion to RA diagnosis was 12 years (interquartile range 8–18, range 1-28). The mean age at diagnosis was 60 years. There was no difference in BMI between women who subsequently developed RA and controls [mean 24.3; standard deviation (SD) 4.1 vs. 24.3 (SD 4.3) kg/m2 ; odds ratio (OR) for RA development 1.02 per SD; 95 % confidence interval (CI) 0.81-1.28]. By contrast, men with a diagnosis of RA during the follow-up had a lower BMI at baseline compared to controls [mean 24.3 (SD 2.7) vs. 25.0 (SD 3.3) kg/m2; OR 0.72 per SD (95 % CI 0.58-0.89)]. The negative association between BMI and RA development in men remained significant in models adjusted for smoking (OR 0.74 per SD; 95 % CI 0.60-0.92) and socio-economic status (OR 0.78 per SD; 95 % CI 0.61-0.99). Men with BMI in the highest quartile (>26.8 kg/m2) had a reduced risk of RA compared to those in the lowest quartile (<22.7 kg/m2) (OR 0.47; 95 % CI 0.26-0.88, adjusted for smoking).
Conclusions In this study, BMI did not affect development of RA in women. In men, a high BMI was associated with a reduced risk of RA. This and the discrepancy from other studies suggest that sex-specific exposures and life style factors that vary across populations modify the impact of BMI on the risk of RA.
Crowson CS et al. Arthrits Care Res 2013; 65: 71-7.
de Hair MJ et al. Ann Rheum Dis 2012 Nov 17. [Epub ahead of print]
Disclosure of Interest None Declared