Income and risk of type 2 diabetes incidence varied associations according to obesity status: a nationwide study

We investigated the association between income parameters and the risk of type 2 diabetes (T2D) influenced by obesity. We analyzed the Korean National Health Insurance Service data (2002–2022), including 3,462,002 adults (aged ≥ 30 years) without diabetes who underwent health examinations in 2012. Income status was assessed annually from 2008 to 2012, and sustained income status was defined as maintaining the same income category for all five consecutive years. Hazard ratios (HRs) for incident T2D were estimated according to income parameters, and stratified by obesity status and BMI categories. During a mean follow-up of 8.73 years, 447,688 T2D cases were identified. Individuals with sustained very low-income (multivariable adjusted HR: 1.599; 95% CI: 1.556–1.642) had a higher hazard of T2D than those who had never been in this condition These associations were stronger in participants without obesity, particularly those with underweight (HR: 2.223; 95% CI: 1.919–2.574 for sustained very low-income; p for interaction < 0.0001). Conversely, a reduced T2D hazard associated with sustained high-income (HR: 0.886; 95% CI: 0.880–0.893) and an increased hazard associated with high income variability (HR: 1.108; 95% CI: 1.098–1.117) were more pronounced in individuals with obesity (p for interaction < 0.0001). Low-income had a greater impact on incident T2D risk among individuals without obesity, whereas among those with obesity, the lower risk observed in sustained high-income groups and the adverse effect of income variability were more pronounced.