title: Paradoxical effect of body mass index on survival in rheumatoid arthritis: role of comorbidity and systemic inflammation.
abstract: BACKGROUND
  Despite high cardiovascular mortality in rheumatoid arthritis (RA), few studies of body mass index (BMI) and obesity as risk factors for death in RA have been published.
  
  
  METHODS
  We estimated the effect of BMI on survival in a cohort of 779 patients with RA adjusting for comorbidity, RA disease severity, erythrocyte sedimentation rate (ESR), and other potential confounders.
  
  
  RESULTS
  The cohort accrued 123 deaths in 3460 person-years (3.6 deaths per 100 person-years; 95% confidence interval [CI], 3.0-4.2). The BMI was inversely associated with mortality. Patients with BMIs of 30 or higher had the lowest mortality, 1.7 deaths per 100 person-years (95% CI, 1.1-2.5). Mortality was higher in each lower BMI category, reaching its highest rate among patients with BMIs lower than 20 with 15.0 deaths per 100 person-years (95% CI, 9.9-23.0). The survival advantage of high BMI was independent of RA onset age, RA duration, sex, ethnic group, socioeconomic status, smoking status, and use of methotrexate but was lost on adjusting for comorbidity and RA severity. We observed an interaction between BMI and ESR, where the BMI protective influence occurred only if the ESR was low. The BMI x ESR interaction was independent of all covariates, including comorbidity and RA severity.
  
  
  CONCLUSIONS
  Body mass has a paradoxical effect on mortality in RA. Patients with high BMI have lower mortality than thinner patients. This effect is mediated in part by comorbidity. The effect of body mass on survival seems to be modified by the level of systemic inflammation.
authors.affiliation: Division of Rheumatology and Clinical Immunology, Department of Medicine, The University of Texas Health Science Center at San Antonio, 78229-3900, USA. escalante@uthscsa.edu
authors.forename: Agustín
authors.initials: A
authors.lastname: Escalante
authors.forename: Roy W
authors.initials: RW
authors.lastname: Haas
authors.forename: Inmaculada
authors.initials: I
authors.lastname: del Rincón
mesh_terms: D000328:Adult; D000368:Aged; D001172:Arthritis, Rheumatoid / Q000097:blood / Q000453:epidemiology / Q000401:mortality*; D001799:Blood Sedimentation; D015992:Body Mass Index; D015331:Cohort Studies; D015897:Comorbidity; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012720:Severity of Illness Index; D015996:Survival Rate; D014481:United States / Q000453:epidemiology