Background/Purpose: Obesity is a known risk factor for OA and hypothesised as a risk factor for RA, although due to different underlying mechanisms. Lower socioeconomic position (SEP) has also been associated with both OA and RA. Given the well-established links between SEP and obesity, there may be interactions between these two risk factors in the development of OA and RA. This study investigated obesity and SEP in relation to incident OA and RA including potential interactions between obesity and SEP.

Methods: The English Longitudinal Study of Ageing (ELSA) is a nationally representative panel study of adults aged ≥50 years, with biannual waves of data collection (2002–2019). Participants with at least one nurse visit measuring height, weight and waist circumference (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. Level of education, occupation (current or last occupation if retired), wealth quintiles and index of multiple deprivation (IMD) quintiles were used as SEP indicators. Outcomes were self-reported incident OA and RA during follow-up. Prevalent OA and RA cases at baseline were excluded for the two different samples; however, people with OA could be included in the RA analyses and vice versa. Weighted Cox proportional hazards models were used to investigate the associations of obesity and SEP indicators with incident OA and RA separately, controlling for baseline covariates. Effect modification of each SEP indicator and obesity was tested by including interaction terms between them. Multiple imputation using chained equations was used to impute missing data on predictors and covariates.

Results: The OA and RA analyses included 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) and 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) participants, respectively. In both samples, more women than men had total and central obesity. Total and central obesity were both associated with incident OA and RA and these associations were maintained after adjustment for covariates, including SEP indicators (Table 1). Those with the lowest education, who are/were employed in manual/routine occupations, who have lower wealth status and were from the most deprived areas were more likely to develop OA and RA; this is seen in basic models and maintained after adjustments for covariates including BMI and WC (Table 1). There was no evidence of effect modification/interactions between obesity and SEP indicators.

Conclusion: Obesity and SEP are both associated with incident OA and RA among adults aged 50 years and older in England and there was no evidence of an interaction between obesity and SEP indicators for incident OA and RA. Although obesity is a known risk factor for OA, the results show that SEP is independently associated with incident OA. Educating rheumatologists and public health experts about the importance of both of these factors, may result in better prevention strategies. To understand underlying mechanisms, further research should investigate the mediators of these associations.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/obesity-and-lower-socioeconomic-position-are-independently-associated-with-incident-osteoarthritis-and-rheumatoid-arthritis-results-from-the-english-longitudinal-study-of-ageing/