Schizophrenia and dementia across the lifespan: epidemiological links, cognitive trajectories, and the pathophysiological interplay

Background: Schizophrenia is a severe psychiatric disorder characterized by persistent cognitive impairment across multiple domains and is increasingly associated with elevated risk of late-life dementia. However, the nature of this association and its underlying mechanisms remain unclear. Objective: This mini-review synthesizes current evidence on dementia risk in schizophrenia, focusing on epidemiology, cognitive trajectories, biological mechanisms, and differential relationships with Alzheimer's disease (AD), vascular dementia (VaD), and frontotemporal dementia (FTD). Results: Epidemiological studies consistently indicate a two- to threefold increased risk of dementia among individuals with schizophrenia, although estimates vary due to diagnostic and ascertainment biases. Cognitive trajectories are heterogeneous: many patients remain cognitively stable over time, while subgroups demonstrate gradual or accelerated decline associated with negative symptoms, medical comorbidities, and social factors. Current evidence does not support a uniform progression toward Alzheimer-type neurodegeneration. Biomarker, neuropathological, and neuroimaging findings suggest distinct biological profiles, with reduced cognitive reserve, neurodevelopmental vulnerability, accelerated aging processes, and vascular and metabolic burden contributing to dementia risk. Genetic overlap between schizophrenia and AD appears modest, whereas partial clinical and molecular convergence is observed with FTD. Screening tools such as MMSE and MoCA may overestimate dementia prevalence due to longstanding baseline cognitive deficits. Sex differences, late-onset psychosis, and cardiometabolic comorbidities further modify risk trajectories. Conclusion: Dementia risk in schizophrenia likely reflects the interaction of lifelong neurodevelopmental vulnerability with aging-related and modifiable factors rather than a disorder-specific neurodegenerative pathway. Longitudinal biomarker-informed studies and tailored diagnostic frameworks are needed to improve differentiation between chronic cognitive impairment and true neurodegeneration.