Understanding the impact of social isolation and loneliness on cognitive function in older adults: longitudinal evidence of trajectories and influencing factors-a systematic review

OBJECTIVES: This review aims to synthesize longitudinal evidence regarding the trajectories of social isolation, loneliness, and cognitive function among older adults, and to examine the associated influencing factors . METHODS: A comprehensive search was conducted in MEDLINE, CINAHL, EMBASE, PsycINFO, and Web of Science from inception to February 23, 2025. Eligible studies employed longitudinal designs to investigate the trajectories of social isolation, loneliness, and cognitive function among older adults. Two reviewers independently extracted data and assessed study quality using the Newcastle-Ottawa Scale. RESULTS: Twenty studies were included. Group-based trajectory modeling was the most commonly used method, with three or four trajectory classes commonly reported. Persistent or increasing social isolation and loneliness were associated with greater cognitive decline and higher dementia risk. Despite general support for loneliness trajectories predicting cognitive outcomes, inconsistencies arose due to differences in contextual, measurement, and data handling. Mediators included depression, health indicators, and biological aging markers, while moderators such as sex, education, and neighborhood factors influenced these relationships. CONCLUSION: This review highlights the dynamic trajectories of social isolation, loneliness, and cognitive function in older adults. Understanding these long-term patterns is important to developing timely and practical interventions that maintain cognitive health in aging populations.