Sustained exposure to low- and high-income status and risk of all-cause mortality in individuals with rheumatoid arthritis: a population-based retrospective cohort study from 2010 to 2020

OBJECTIVE: Although socioeconomic status has been linked to various rheumatoid arthritis (RA)-related outcomes, evidence on the association of sustained income status with mortality among patients with RA remains limited. METHODS: We followed a nationally representative cohort of 50 600 Korean adults aged ≥40 years newly diagnosed with RA between 2010 and 2017 through 31 December 2020. Income status, based on monthly health insurance premiums, was tracked over the 5-year period preceding diagnosis. Primary exposure included the cumulative years in a low- or high-income status. The outcome was all-cause mortality. Cox proportional hazards models were used to estimate HRs after adjusting for sociodemographic, behavioural and clinical covariates. We conducted a comprehensive stratified analysis using a range of relevant factors. RESULTS: Sustained low-income status was significantly associated with increased mortality in a dose-response manner among patients aged <65 years, even after adjusting for income status at diagnosis (p for trend=0.011 vs 0.374 in older patients). Sustained high-income status was associated with reduced mortality in both age groups, with a stronger association observed in younger patients (adjusted HR (95% CI) for 5-year high-income exposure: 0.50 (0.38-0.64) in patients aged <65 years versus 0.74 (0.62-0.88) in patients ≥65 years). Rural residence further amplified the adverse effects of prolonged low-income exposure. CONCLUSIONS: Persistent low-income status increases mortality risk among younger patients with RA, a group often overlooked by policy interventions. Policies that address the sustained economic disadvantages beyond short-term assistance are required.