Longitudinal associations of sustained low or high income and income variability with incident cardiovascular disease in individuals with type 2 diabetes: a retrospective population-based cohort study

Abstract

ABSTRACTBackground and AimsLongitudinal change in income is crucial in explaining cardiovascular health inequalities, but there is limited evidence for cardiovascular disease (CVD) risk associated with income dynamics over time among individuals with type 2 diabetes (T2D).MethodsUsing a nationally representative sample from the Korean Health Insurance Service database, 1,528,108 adults with T2D aged 30-64 years and no history of CVD were enrolled between 2009-2012 (mean follow-up of 7.3 years). Using monthly health insurance premiums information, income levels were assessed annually for 4 years before the baseline year. Income variability was defined as the intraindividual standard deviation of the percent change in income across 5 years. The primary outcome was a composite event of incident fatal and nonfatal CVD (myocardial infarction, stroke, and heart failure) using insurance claims. Hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated after adjusting for potential confounders.ResultsSustained low income (i.e., lowest income quartile) over 5 years was associated with increased CVD risk (HRn=5yearsvs.n=0years1.38, 95% CI 1.35-1.41; Ptrend<0.0001), whereas sustained high income (i.e., highest income quartile) was associated with decreased CVD risk (HR 0.71n=5yearsvs.n=0years95% CI 0.70-0.72; Ptrend<0.0001). High-income variability was associated with increased CVD risk (HRhighestvs.lowestquartile1.25, 95% CI 1.22-1.27; Ptrend<0.001). Individuals who experienced an income decline across 5 years leading up to baseline had increased CVD risk, particularly in a decrease to the lowest income level (i.e., Medical Aids beneficiaries), regardless of initial income status. Sensitivity analyses, including potential mediators, such as lifestyle-related factors and obesity, supported the results.ConclusionsAmong non-elderly Korean adults with T2D, sustained low income, higher income variability, and income declines were associated with increased CVD risk. Our findings highlight the need to understand better the mechanisms by which income dynamics impact CVD risk among individuals with T2D.