Incidence of early-onset type 2 diabetes and sociodemographic predictors of complications: A nationwide registry study

Aims: Early-onset type 2 diabetes (T2DM) (18-45 years) is rising globally, yet complication incidence in this group remains unclear. We investigated the incidence of early-onset T2DM, the incidence of micro- and macrovascular complications, and how comorbidities (e.g., severe mental illness) and sociodemographic factors (e.g., education level) influence complication risk and timing in Denmark. Methods: Using nationwide registers, we followed 8,129,005 individuals from 1996 to 2020 to estimate the incidence rate (IR) of early-onset T2DM. 49,850 individuals with early-onset T2DM were followed to calculate IRs for microvascular (nephropathy, retinopathy) and macrovascular (cardiovascular disease, amputation) complications. Incidence rate ratios (IRRs) assessed associations between comorbidities, sociodemographic factors, and complications. Poisson regression models calculated IRs and IRRs. Results: From 1996 to 2020, the IR of early-onset T2DM more than doubled in men and tripled in women, with women dominating younger age groups. During follow-up (7.9-9.8 years), 37.6 % developed complications. Higher complication IRs were observed in men, those with sociodemographic disadvantages, and individuals with comorbidities. Early complications (<= 5 years) were more common among the unemployed, single individuals, and those with comorbidities. Conclusions: The rising IR of early-onset T2DM in younger women, and complications disproportionately affecting men and those with comorbidities or sociodemographic disadvantages, highlight the need for targeted interventions.