Living alone and risk of dementia, cognitive decline, and institutionalization in the MEMENTO cohort.

Introduction: Alzheimer's disease and related dementias (ADRD) represent a public health challenge, with prevention strategies focusing on modifiable risk factors such as isolation. Living alone is used as a proxy for social isolation, although its relationship with ADRD outcomes remains unclear, partly due to the distinction between objective isolation and subjective loneliness. This study examined the association between living alone and the risk of dementia, cognitive decline, and institutionalization in the MEMENTO cohort, a French clinic-based study of individuals with cognitive complaints or mild cognitive impairment. Methods: Living alone at baseline was the main exposure. Perceived isolation was assessed using self-reported measures. Outcomes included incident dementia, institutionalization; and trajectories of Mini-Mental State Examination (MMSE) scores over a 5-year median follow-up. Cause-specific Cox models accounting for competing risks were used for dementia and institutionalization, and linear mixed models for MMSE trajectories. Results: Among 2,269 participants (median age 71.5 years, 62% women, median MMSE 28), 30.7% lived alone and 6.5% reported perceived isolation. At 60 months, estimated cumulative incidences were 15% for dementia, 1.0% for institutionalization and 3.6% for death. Living alone was not associated with incident dementia (HR = 0.88 [95%CI: 0.67-1.16], p = 0.38), or cognitive decline. In contrast, it was associated with a higher risk of institutionalization (HR = 3.21 [95%CI: 1.09-9.48], p = 0.03). Discussion: Living alone was not linked to dementia risk or cognitive decline, but was associated with a higher risk of institutionalization. This finding may indicate that living alone captures vulnerability related to reduced day-to-day support rather than cognitive decline itself.