The Association Between Social Isolation and Incident Dementia Among Older Adults: Evidence From National Health and Aging Trend Study.

Background and Objectives: Older adults are vulnerable to social isolation, making it crucial to understand its impact on dementia risk. Yet, existing evidence lacks consistency, with studies using varied measures of social isolation and overlooking potential confounders. We aim to investigate the associations between social isolation and dementia risk among older adults, hypothesizing that this association may diminish after adjusting for confounding factors. Research Design and Methods: We used 2 977 community-dwelling older adults who had no dementia in 2015 from National Health and Aging Trends. Group-based trajectory modeling was used to analyze the trajectories of social isolation, depression, and anxiety from 2011 to 2015. Cox proportional hazards regression models were then employed to estimate the association between social isolation trajectories and incident dementia from 2015 to 2022, adjusting for demographic variables, depression, anxiety, self-rated health, smoking status, and cardiovascular disease-related variables. Results: Three social isolation trajectories were identified: minimal, moderate, and high levels of social isolation. During a mean follow-up of 3.6 years, 19.0% of participants were diagnosed with dementia. When only demographics were adjusted, individuals in the moderate social isolation group were 22% less likely to develop dementia compared to those with high social isolation. This association between social isolation and incident dementia became nonsignificant after further adjustment for depression, anxiety, and health indicators. Discussion and Implications: The association between social isolation and dementia risk may be mediated by factors such as depression and other health indicators.