Effect of body mass index on mortality and clinical status in rheumatoid arthritis

Abstract

To study the relative risk (RR) of all-cause and cause-specific mortality in rheumatoid arthritis (RA) associated with body mass index (BMI), and to quantify the clinical and outcome consequences of abnormal BMI. We studied mortality in 24,535 patients over 12.3 years, dividing patients into 3 age groups, <50, 50-70, and >70 years and fit Cox regression models separately within each age stratum. We used BMI categories of <18.5 kg/m(2) (underweight), 18.5 to <25 kg/m(2) (normal weight, reference category), 25 to <30 kg/m(2) (overweight), and ≥30 kg/m(2) (obesity). BMI ≥30 kg/m(2) was seen in 63-68% and underweight in ~2%. Reduction in the RR (95% confidence interval [95% CI]) for all-cause (AC) and cardiovascular mortality was seen for overweight (AC 0.8 [95% CI 0.8, 0.9]) and obese groups (AC 0.8 [95% CI 0.7, 0.8]), with and without comorbidity adjustment. Underweight was associated with increased mortality risk (AC 1.9 [95% CI 1.7, 2.3]). By contrast, obesity produced profound changes in clinical variables. Compared with normal weight, the odds ratio in the obese group was 4.8 for diabetes mellitus, 3.4 for hypertension, 1.3 for myocardial infarction, 1.4 for joint replacement, and 1.9 for work disability. Total semiannual direct medical costs were $1,683 greater, annual household income $6,481 less, pain scores 1.1 units higher, Health Assessment Questionnaire 0.28 higher, and EuroQol utility 0.7 units lower in the obese. Overweight and obesity reduce the RR of all-cause and cardiovascular mortality across different age groups and durations of RA. By contrast, overweight and obesity are associated with substantial increased risks of comorbidity, total joint replacement, greater pain, medical costs, and decreased quality of life.