Type 2 Diabetes Mellitus as a Risk Factor for Dementia and Alzheimer’s Disease: A Narrative Review

Background Type 2 diabetes mellitus (T2DM) is associated with cognitive impairment and dementia. The underlying mechanisms and the effectiveness of preventive interventions remain incompletely understood. Aim To review the association between T2DM and dementia risk, with particular emphasis on Alzheimer’s disease. Materials and Methods This narrative review included 53 publications identified through PubMed and Google Scholar searches conducted in May and June 2026, covering publications from January 2015 to June 2026. Reference lists were screened for additional sources. Eligible publications were written in English, with an exception for Polish national clinical guidelines. Publications without accessible full texts were excluded. Evidence was synthesized narratively. Results T2DM was associated with increased dementia risk, with a generally stronger association for vascular dementia than for Alzheimer’s disease. Proposed mechanisms included cerebral insulin resistance, oxidative stress, inflammation, and vascular injury. However, the evidence did not establish that T2DM directly causes Alzheimer’s disease. Longer diabetes duration, hypoglycaemia, and greater HbA1c variability were associated with higher dementia risk, while findings concerning mean HbA1c required cautious interpretation. Cognitive impairment may compromise diabetes self-management. Evidence concerning antidiabetic medications differed across drug classes and study designs. A meta-analysis of randomized trials reported a lower risk of dementia or cognitive impairment with GLP-1 receptor agonists, but limitations in outcome ascertainment and follow-up restrict its implications for prevention. Conclusions T2DM is associated with increased dementia risk. Cognitive difficulties should be considered within comprehensive diabetes care, but the reviewed evidence does not establish a specific glycaemic target or pharmacological intervention for dementia prevention. Further trials with adequate follow-up and systematic assessment of cognitive outcomes are needed.