Background/Purpose

Low body mass index (BMI) is a risk factor for poor long-term outcomes in rheumatoid arthritis (RA). Low BMI in RA has been speculated to reflect weight loss due to the greater resting energy expenditure among subjects with more active and severe RA. We determined predictors of change in BMI in RA, and specifically examined whether greater disease activity was associated with weight loss over time.

Methods

Subjects from the Veterans Affairs RA Registry (VARA) (n=1396) were studied. Information on inflammatory markers, presence of erosions, and smoking status were extracted from the VARA database. VARA participants without longitudinal data were excluded (n = 349) but were similar in age, gender, race, and enrollment BMI (data not shown). BMI was extracted from the vital signs package from VA electronic medical records within 14 days of each visit date. VA pharmacy records were queried to identify prescriptions for specific RA therapies within 1 month of each visit. Robust Generalized Estimating Equations (GEE) regression models determined independent associations between pre-hypothesized clinical variables and change in BMI (or odds of weight loss >1 kg/m²) over the subsequent observation period. Variables were either time-varying (log-transformed C-Reactive Protein [lnCRP] and medication use) or time-invariant (baseline CCP seropositivity, erosive disease, and smoking status).

Results

Increasing age, current smoking, and the presence of erosions at baseline were associated with lower BMI (all p<0.001). On average, weight decreased over time [β: -0.017 (-0.029, -0.0052) p=0.005]. Higher ln(CRP), current smoking at baseline, greater baseline BMI, and older age were associated with greater reductions in BMI over the subsequent observation period (Table 1) (all p<0.01). Higher ln(CRP), current smoking, greater baseline BMI, and older age were also associated with a greater risk of weight loss over the subsequent observation period (Table 1) (all p<0.01). Methotrexate use was associated with a lower risk of weight loss (p=0.002). The use of prednisone and the use of anti-TNF therapies were not associated with change in BMI or the risk of weight loss.

Conclusion

Greater age, greater inflammatory activity, and current smoking are associated with weight loss in RA. The weight loss (and lack of weight gain) among subjects with inflammation may be due to the greater resting energy expenditure and catabolism seen with the active inflammatory process. While methotrexate was associated with a decreased risk of weight loss, there were no consistent associations between other RA medications and changes in weight.

Abbreviations: Obs= Observations; CI= Confidence Interval; BMI= Body Mass Index; CRP= C-Reactive Protein; TNF= Tumor Necrosis Factor Inhibitor; CCP= Cyclic Citrullinated Peptide Ab