Both socioeconomic position (SEP) and obesity are associated with the development of incident osteoarthritis (OA) among men and women, with body mass index (BMI) mediating the relationship between a lower SEP and incident OA, according to study results published in Seminars in Arthritis and Rheumatism.
Researchers analyzed data derived from the English Longitudinal Study of Ageing, a large longitudinal panel analysis that documented the health, social, and economic circumstances of individuals aged 50 years or older and their partners who resided in private households in England. The original sample in 2002, along with refreshment samples in 2006, 2008, 2012, and 2014, was obtained from the Health Survey of England (HSE).
The researchers measured SEP using education, income, wealth, occupation, and deprivation. Obesity was defined as a BMI of at least 30 kg/m2. Cox regression analyses were conducted to explore the associations between SEP and obesity at baseline and self-reported incident OA.
The sample population comprised a total of 9281 individuals. The number of person-years included in the analysis was 65,456. During a mean follow-up of 7.8 years, 25.5% (2369 of 9281) of the participants developed OA. Those who developed OA were more frequently women, were older, had a lower level of education, and had higher total and central obesity rates at baseline compared with participants who did not develop OA.
Participants with a lower SEP were more likely to develop OA than those with a higher SEP (hazard ratio [HR] of the lowest vs highest education category, 1.52; 95% CI, 1.30-1.79).
Formal tests evaluating the interaction between SEP indicators and gender or obesity did not demonstrate statistical significance (P ≤.89), except for the interaction between gender and deprivation (P =.014). Per stratified analysis, the relationship between higher deprivation and incident OA was stronger among men (HR of most vs least deprived, 1.89; 95% CI, 1.46-2.46) than among women (HR, 1.33; 95% CI, 1.07-1.64).
Both total and central obesity were associated with incident OA; these relationships remained the same after adjusting for such covariates as SEP indicators. The risk for incidence of OA increased by 1% for each 1-kg/m2 increase in BMI and for each 5-cm increase in waist circumference (WC). Obesity vs nonobesity was associated with increased rates of incident OA (HR, 1.37; 95% CI, 1.23-1.52). Although BMI mediated the link between a lower SEP and OA (P <.001), the direct effect was not statistically significant (P =.212).
Limitations of the study include self-reported OA diagnosis, which may lead to misclassification or recall bias. Additionally, BMI and WC at baseline only were included as no early life data were available.
The study authors conclude, “Efforts to reduce obesity, specifically in low SEP groups, may help to decrease the risk for OA.”