Income level and the risk of incident dementia among adults aged 50 with newly diagnosed type 2 diabetes: a population-based cohort study using the NHIS-Senior database in South Korea

BMJ Open. 2026 Jul 6;16(7):e112641. doi: 10.1136/bmjopen-2025-112641.

ABSTRACT

INTRODUCTION: Type 2 diabetes mellitus (T2DM) is a well-established independent risk factor for dementia and is associated with dementia pathophysiology; however, the role of income level remains uninvestigated in this patient population. The aim of this study was to examine the association between income level and incident dementia risk among adults aged ≥50 years with newly diagnosed T2DM.

RESEARCH DESIGN AND METHODS: We conducted a retrospective population-based assessment of Korean National Health Insurance Service-Senior Cohort (2002-2019) data. Individuals aged ≥50 years with a new primary or secondary diagnosis of T2DM from 2004 onward were included. Sex and income level were assessed. Subgroup analyses were performed to examine differences in dementia risk across income levels and assess whether associations between income levels and dementia risk varied by dementia subtype.

RESULTS: Among women with newly diagnosed type 2 diabetes, those in the low-income group showed a significantly higher risk of incident dementia compared with the high-income group (deciles 9-10) (HR=1.19, 95% CI 1.11 to 1.28). In men with newly diagnosed type 2 diabetes, a significant increase in dementia risk was observed only among Medical Aid recipients relative to the high-income group (HR=1.44, 95% CI 1.18 to 1.77). Similarly, women within this patient population showed significantly elevated risks among Medical Aid recipients (HR=1.33, 95% CI 1.11 to 1.61) and those in the first income decile. Subtype analyses further revealed that being a Medical Aid recipient was associated with an increased risk of vascular dementia in men, while lower income levels (including Medical Aid recipients and deciles 1 and 3) were associated with a higher risk of Alzheimer's disease in women all in comparison to their high-income counterparts.

CONCLUSIONS: Among middle-aged and older adults with newly diagnosed T2DM, having a lower income was significantly associated with elevated dementia risks, with the greatest risk observed among low-income women. The association between income level and dementia risk differed by dementia subtype, with vascular dementia and Alzheimer's disease being more prevalent among low-income men and low-income women, respectively. These findings highlight the need for sex-specific and income-specific dementia prevention strategies.

PMID:42409396 | PMC:PMC13343042 | DOI:10.1136/bmjopen-2025-112641