Article Text
Abstract
Background Body mass index (BMI) and waist circumference (WC) are the measures most commonly used to identify total and central obesity, respectively. Research on the associations between obesity and incident rheumatoid arthritis (RA) and osteoarthritis (OA) is limited, particularly for central obesity. Therefore, we investigated the associations between obesity defined by both BMI and WC and incident RA and OA in England.
Methods The English Longitudinal Study of Ageing (ELSA) is a nationally representative panel study of non-institutionalised adults aged ≥50 years, with biannual waves of data collection (2002–2019). Participants with at least one nurse visit measuring height, weight and WC and one follow-up assessment were included in this study. BMI of ≥30kg/m2 and WC ≥102 cm for men and ≥88 cm for women defined total and central obesity, respectively. Outcomes were self-reported incident RA and OA during follow-up. Prevalent RA or OA cases at baseline were excluded. Cox proportional hazards models were used to investigate the associations between total and central obesity and incident RA and OA separately, controlling for baseline covariates (i.e. age, gender, ethnicity, education, occupation, wealth, smoking and alcohol consumption). Gender differences were formally tested by including interaction terms between gender and obesity. Analyses were conducted using Stata v14.
Results The RA and OA analyses included 10,931 (54.1% female; mean age 64.0 (standard deviation (SD) 9.6); mean follow-up 8.8 (SD 4.2) years; and 1,216 incident cases of RA) and 9,281 (51.3% female; mean age 63.6 (SD 9.6); mean follow-up 7.8 (SD 4.2) years; and 2,369 incident cases of OA) participants, respectively. In both samples, more women than men had total and central obesity. Total and central obesity were both associated with incident RA and these associations were maintained after adjustment for covariates (fully-adjusted hazard ratios (HRs) 1.58 (95% confidence interval (CI) 1.39, 1.80) and 1.43 (95% CI 1.25, 1.62), respectively). Similarly, total and central obesity were both associated with incident OA (fully-adjusted HRs 1.45 (95% CI 1.32, 1.60) and 1.42 (95% CI 1.30, 1.55), respectively). There was no evidence of gender differences in any of these associations (p-values from tests of interaction >0.33).
Conclusion Both total and central obesity were associated with increased rates of RA and OA among adults aged 50 years and older. There were no gender differences for these associations. Education about obesity and the development of both RA and OA may result in better prevention or early intervention strategies.