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Type 2 diabetes mellitus (T2DM) is increasingly recognized as a major risk factor for Alzheimer's disease (AD), with mounting evidence highlighting shared pathophysiological mechanisms. This review explores the intricate biological and molecular links between these two chronic disorders. Key overlapping pathways include impaired insulin signaling, chronic inflammation, oxidative stress, mitochondrial dysfunction, amyloid-beta (Aβ) accumulation, tau hyperphosphorylation, and the formation of advanced glycation end-products (AGEs). Disruption of insulin signaling in the brain contributes to synaptic loss and neurodegeneration, while systemic metabolic disturbances aggravate blood-brain barrier dysfunction and neurovascular damage. Emerging studies also underscore the role of antidiabetic treatments, especially newer agents targeting the gut-brain axis, in modulating AD progression. The review further examines preclinical models, clinical observations, and the development of biomarkers to improve early detection and intervention. Despite growing insights, challenges remain in translating mechanistic knowledge into effective therapies. A multidisciplinary approach integrating metabolic control and neuroprotective strategies is essential for addressing the comorbid burden of T2DM and AD. See also the graphical abstract(Fig. 1).