The Associations between Socioeconomic Position, Obesity and the Development and Progression of Arthritis

Abstract

Aim: Consistent evidence suggests that people with lower socioeconomic position (SEP) are more likely to be obese. Although research points towards social inequalities in arthritis, prospective cohort studies are lacking. Obesity is also related to both osteoarthritis (OA) and rheumatoid arthritis (RA). This PhD project aimed to improve our understanding of the complex relationships between SEP, obesity and the development and progression of OA and RA. Methods: First, a systematic literature review (SLR) and a meta-analysis were performed to summarise the current understanding of the relationship between SEP and obesity. Meta-regression analyses were performed to investigate differences between measures of obesity (body mass index (BMI) and waist circumference (WC)) and gender. Then, using longitudinal data from the English Longitudinal Study of Ageing (ELSA) and the Rheumatoid Arthritis Medication Study (RAMS), the relationships between different indicators of SEP (education, occupation, income, wealth and area-level deprivation), obesity (BMI of 30 kg/m2 or higher) and the development and progression of arthritis were investigated. Cox regression analyses estimated associations of SEP and obesity with incident arthritis and knee joint replacement surgery (JRS) in OA. Linear mixed models were used to study associations of SEP and obesity with repeated measures of disability and disease activity scores in OA and RA. Structural equation modelling and causal mediation analyses were performed to estimate the mediating effect of BMI on the relationships between lower SEP and the development and progression of OA and RA. Results: The SLR indicated an association between having a lower education and obesity; this relationship was stronger among women than men (adj odds ratio (OR) women vs men 1.66 (95% CI 1.32, 2.08)). Only in men, the relationship was found to be stronger for obesity measured by WC compared to obesity measured by BMI (adjOR central vs total obesity in men 1.27 (95% CI 0.97, 1.67)). In ELSA, lower SEP was associated with higher rates of OA and RA (adj hazard ratios (HRs) lowest vs highest education category OA: 1.52 (95% CI 1.30, 1.79); RA: 2.23 (95% CI 1.74, 2.86)), which was mediated through BMI (completely for OA and partially for RA). Lower SEP was also associated with increased functional limitations over time in people with knee OA (e.g. difficulty walking 100 yards: no qualification vs degree adjOR 4.33 (95% CI 2.20, 8.55)). A small proportion of the association between lower SEP and functional limitations could be explained by BMI (6.2% to 12.5%). Those with lower SEP were less likely to have knee JRS (e.g. adjHR most vs least deprived 0.37 (95% CI 0.19, 0.73)). Using RAMS, deprivation was associated with higher disability (adj regression coefficients highest vs lowest deprivation fifths 0.32 (95% CI 0.19, 0.45)) and disease activity (0.34 (95% CI 0.11, 0.58)). BMI mediated part of the association between higher deprivation and self-reported disability (14.24%) and disease activity scores (17.26%). Conclusion: Lower SEP is associated with the development and progression of arthritis, partially mediated through BMI. These findings illustrate the need to investigate the effectiveness of weight management strategies in people with arthritis from lower SEP.

Date of Award	1 Aug 2023
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Suzanne Verstappen (Supervisor), James Gwinnutt (Supervisor) & Jenny H Humphreys (Supervisor)