Sex differences in assessment of obesity in rheumatoid arthritis

Objective To determine the prevalence of obesity and how accurately standard anthropometric measures identify obesity among men and women with rheumatoid arthritis (RA). Methods Dual x-ray absorptiometry (DXA) was performed for 141 persons with RA (56 men and 85 women). Two anthropometric proxies of obesity (body mass index [BMI] and waist circumference [WC]) were compared to a DXA-based obesity criterion. Receiver operating characteristic curves determined optimal cut points for each anthropometric measure, relative to DXA. The association of body fat and anthropometric obesity measures with disease status and cardiovascular risk was assessed in multiple regression analyses, controlling for age and glucocorticoid use. All analyses were performed separately for men and women. Results A total of 20%, 32%, and 44% of women and 41%, 36%, and 80% of men were classified as obese by BMI, WC, and DXA, respectively. Cut points were identified for anthropometric measures to better approximate DXA estimates of percent body fat (BMI =26.1 kg/m2 for women and =24.7 kg/m2 for men; WC =83 cm for women and =96 cm for men). For women and men, higher percent fat was associated with poorer RA status. Anthropometric measures were more closely linked to RA status for women, but identified cardiovascular risk for both women and men. Conclusion A large percentage of this RA sample was overfat; DXA-defined obesity was twice as common in men as in women. Utility of revised BMI and WC cut points compared to traditional cut points remains to be examined in prospective studies, but results suggest that lower, sex-specific cut points may be warranted to better identify individuals at risk for poor RA and/or cardiovascular outcomes.