Incidence and risk of Alzheimer’s disease in individuals with type 2 diabetes: a systematic review and meta-analysis

Abstract Background Epidemiological evidence links type 2 diabetes (T2D) to an increased risk of dementia, including Alzheimer’s disease (AD). However, previous syntheses often combined heterogeneous diabetes and dementia definitions and have not comprehensively quantified AD incidence among individuals with T2D. We aimed to estimate both the incidence of AD among individuals with T2D and the association between T2D and AD using studies with well-defined T2D and AD outcomes. Methods We systematically searched MEDLINE, CINAHL (via EBSCO), Embase (via Ovid), and Scopus from inception to April 2026 for studies investigating the incidence of AD among individuals with T2D or the association between T2D and AD. Data were pooled using random-effects models and presented as incidence rates and adjusted relative risks (RRs) with 95% confidence intervals (CIs). Results Of the 9,430 articles identified, 40 studies involving 27,102,559 participants were included. Twenty-three studies contributed incidence data, and 26 reported adjusted relative risks (aRR). The pooled incidence of AD among individuals with T2D was 4.71 per 1,000 person-years (95% CI 3.31–6.71). T2D was associated with an increased risk of AD (aRR 1.53, 95% CI 1.38–1.70). Subgroup findings were generally consistent, results were robust in sensitivity analyses, and no publication bias was detected. Conclusions This study provides a comprehensive quantification of the AD burden associated with T2D by focusing on well-defined AD and T2D outcomes and advancing the field beyond prior broad dementia syntheses. Integrating incidence and relative risk estimates clarifies both the absolute and relative burden of AD in T2D and extends previous syntheses that primarily emphasised relative risk. Individuals with T2D experienced approximately five AD cases per 1,000 person-years and a 53% higher risk of AD, supporting the rationale for integrating cognitive risk prevention into diabetes care.