Background The links between adipose tissue and inflammation on the one hand and obesity and joint dysfunction on the other, are well established. However, how these translate into clinical disease activity and functional disability in rheumatoid arthritis (RA), remains to be clearly defined.
Objectives To investigate the association between BMI and 1. The achievement of disease remission or low disease activity and 2. Functional ability, in RA.
Methods Data from two consecutive UK multi-centre RA inception cohorts with similar design were used: the Early RA Study (ERAS) and Early RA Network (ERAN). Recruitment figures/median follow up for ERAS and ERAN were 1465/10 years (maximum 25 years), and 1236/6 years (maximum 10 years) respectively. Standard demographic and clinical variables were recorded at baseline and then annually until loss to follow-up or the end of study follow-up. Multilevel logistic regression analysis was used with either remission (R-DAS) or low disease activity status (L-DAS) and health assessment questionnaire (HAQ, <1 vs ≥1) as the dependent categorical variables of interest in models adjusting for patient, disease-related clinical variables and recruitment year. BMI was examined in separate models as both a continuous and categorical predictor variable according to WHO definitions: underweight (BMI less than 18.5), normal (BMI between 18.5 and 25), overweight (BMI between 25 and 30) and obese (BMI greater than 30). BMI was included in the models relating to the same time point as the outcome assessed.
Results Baseline BMI data from 2420 patients (90%) indicated that 40.0% had BMI scores in the normal range, 1.8% were underweight, 37.2% were overweight and 21.3% were obese. Mean BMI increased slightly over time from 26.5 at baseline to 26.8 at 2 years and then 27.1 at 5 years. In multilevel logistic models adjusting for age, sex, smoking status, antibody status, haemoglobin, erosions and year of recruitment, higher BMI was associated with reduced odds of achieving R-DAS (OR 0.97;95% CI 0.95, 0.99) (table) and L-DAS, although the latter did not reach statistical significance (OR 0.98;95% CI0.96, 1.00). Obesity was related to a significantly lower chance of R-DAS by 29% (OR 0.71;95% CI 0.55, 0.93) and L-DAS by 31% (OR 0.69;95% CI 0.55,0.87). Higher BMI was predictive of higher disability (OR 1.04;95% CI 1.01,1.06). More specifically, obesity increased the odds of higher disability by 63% (OR 1.63;95% CI 1.20,2.23) and in the same models, higher DAS was also strongly predictive of higher disability (OR 3.67;95% CI 3.41,3.95).
Conclusions The findings support a link between higher BMI and worse clinical outcomes, namely disease activity and functional ability. Obesity was associated with lower levels of both remission and low disease activity states, and of higher disability. The findings highlight the importance of monitoring the patients' weight, screening and targeting obesity as part of routine clinical practice, in order to improve disease outcomes. This work provides clinical insights into the role of BMI on disease outcomes in RA.
Disclosure of Interest None declared