Obesity partly explains the effect of socioeconomic position on multiple long-term conditions in UK Biobank

The mechanisms through which lower socioeconomic position (SEP) leads to increased risk of multiple long-term conditions (MLTC) are poorly understood. Using data from UK Biobank (n = 194,038), we applied four-way decomposition to investigate the mediating and moderating roles of overall (body mass index [BMI] > 30 kg/m 2 ) and central (waist-to-hip ratio > 0.85 [females]/ > 0.9 [males]) obesity in the association between SEP (indicated by educational attainment) and incident MLTC. Incident MLTC was defined as the diagnosis of two LTC of interest from linked healthcare data. Over five-years follow up, 11,071 participants developed MLTC. Socioeconomic inequalities in MLTC were observed and partly mediated by overall and central obesity. For example, compared with degree educated participants, those with no qualifications had an approximately 71% (95%CI 59%, 77%) higher rate of MLTC. The proportion mediated by overall obesity was 8% (6%, 11%) and central obesity was 13% (10%, 16%). Approximately one fifth of this total effect was attributable to interaction between SEP and central obesity. A hypothetical intervention eradicating central obesity could eliminate around one third of socioeconomic inequalities in incident MLTC. Obesity partly mediated the association between SEP and incident MLTC and targeting different indices of obesity could reduce socioeconomic inequalities in MLTC.