Does insomnia severity increase the risk of dementia? A 7-year longitudinal study

Although sleep disorders may be a modifiable risk factor for dementia onset, the association between insomnia and dementia remains unclear. The aim of this study was to examine whether the severity of insomnia accelerates the onset of dementia among older adults.

This 7-year community-based longitudinal study was conducted in Tsuru City, Yamanashi, Japan. All residents aged ≥65 years without functional disability were invited to participate in the baseline survey in January 2016, and 5255 older adults responded. Follow-up data were collected for up to seven years and included in the analysis. Dementia onset was assessed using data from long-term care insurance. Insomnia severity was measured using the Athens Insomnia Scale. Restricted cubic spline models and time-varying Cox proportional hazards models were conducted to examine the association between insomnia severity and dementia onset.

During the follow-up period, 878 participants (16.7%) developed dementia. The spline curve indicated a linear dose-response association between insomnia severity and dementia risk. After adjusting for sociodemographic factors and health characteristics, greater insomnia severity was associated with a higher incidence of dementia (hazard ratio [95% confidence interval]: 1.02 [1.00, 1.04]). Stratified analyses by sex, age, and educational attainment, as well as sensitivity analyses excluding participants who developed dementia within two years of baseline, showed results consistent with the main analyses.

We found a linear dose-response relationship, in which greater insomnia severity is associated with a higher risk of dementia. These findings support the importance of prevention and management of insomnia in dementia prevention strategies.