Income dynamics and risk of early-onset dementia: a nationwide cohort study

The relationship between income dynamics-including sustained income level, income changes, and income variability-and early-onset dementia (EOD) has not been well established. This study investigated the association between income dynamics and the risk of EOD.

This cohort study included 2,247,461 adults aged 40-60 years who underwent health examinations in 2012 through the Korean National Health Insurance Service, with a median follow-up duration of 5.4 years till 2018. Income status was assessed for 2012 and the 4 preceding years using monthly health insurance premiums, and income-related parameters were derived from this pre-baseline 5-year window. Income variability was defined as the intra-individual standard deviation of four consecutive annual percentage changes. Hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated to evaluate the relationship between income dynamics and EOD risk, adjusting for potential confounders.

Sustained low-income status over five years was associated with an increased risk of EOD (HR for 5 years vs. 0 years 1.63, 95% CI 1.49-1.78; P-trend < 0.001), whereas sustained high-income status was associated with a reduced EOD risk (HR for 5 years vs. 0 years 0.55, 95% CI 0.51-0.59; P-trend < 0.001). Notably, higher income variability was linked to a greater risk of EOD (HR for highest vs. lowest quartile 1.37, 95% CI 1.28-1.48; P-trend < 0.001). The decline in income-particularly to the lowest level (Medical Aid beneficiaries)-was associated with an elevated risk of EOD, irrespective of the initial income status.

Sustained low income, income decline, and greater income variability were associated with higher EOD risk. These findings may help identify socioeconomically vulnerable middle-aged adults for targeted dementia risk assessment and prevention.