Association between body mass index and anti-citrullinated protein antibody-positive and anti-citrullinated protein antibody-negative rheumatoid arthritis: results from a population-based case-control study.

Objective: Being overweight or obese is associated with many chronic diseases, but previous studies of the association with rheumatoid arthritis (RA) have shown inconsistent results. The aim of this study was to investigate the association between body mass index (BMI) and the risk of developing the 2 main subtypes of RA.

Methods: At inclusion, cases and controls answered questions about their weight and height and donated blood samples. The presence of antibodies to citrullinated protein antigens (ACPAs) was analyzed among 2,748 cases and 3,444 controls (28% men). Odds ratios (ORs) and 95% confidence intervals (95% CIs) were calculated using conditional logistic regression.

Results: Compared to those with normal weight (BMI <25 kg/m(2) ), the adjusted overall OR for developing ACPA-negative RA was 1.1 (95% CI 0.9-1.3) for overweight individuals (BMI ≥25 to <30 kg/m(2) ) and 1.4 (95% CI 1.1-1.9) for obese individuals (BMI ≥30 kg/m(2) ). When stratified by sex, the OR for ACPA-negative RA for obese women was 1.6 (95% CI 1.2-2.2), and there was no association between obesity and ACPA-negative RA in men (OR 1.1, 95% CI 0.6-1.8). In obese men compared to men with normal weight, the OR for ACPA-positive RA was 0.6 (95% CI 0.3-0.9), while there was no association between BMI and ACPA-positive RA among women (OR 1.0, 95% CI 0.8-1.2).

Conclusion: Our findings show that obesity is associated with developing ACPA-negative RA in women, and indicate an inverse association between BMI and ACPA-positive RA in men.