The association between chronotype and incident dementia: exploring age, educational-attainment and sex differences

Chronotype reflects individual variation in circadian rhythm (CR) (e.g., morningness versus eveningness). CR and chronotype have been associated with dementia pathology, and recent literature suggests that impaired sleep quality and CR disturbances may represent relevant causal factors for dementia. Current evidence is scarce and consists of just a small number of cross-sectional analyses and one longitudinal study. The aim of this study is to investigate the longitudinal association between chronotype and dementia risk in the older adult population, aged 60 years and older.

Linking data from the Lifelines Cohort Study and data from Vektis obtained by Statistics Netherlands led to a sample for analysis of n = 16,757 participants. Chronotype was measured with the Munich ChronoType Questionnaire (MCTQ) between 2011 and 2015. Chronotype was categorised into five categories: extremely early, slightly early, intermediate, slightly late, extremely late. Dementia incidence was based on having at least one dementia indicator from the Vektis dataset in the years 2018 until 2024. A discrete-time survival model was used to examine the association between chronotype and dementia. Age was specified as the underlying time scale in the discrete-time logistic survival analysis. Sex was included as a covariate. Interactions between age, sex, and educational attainment and chronotype were measured by including relevant interaction terms in the model.

The median age in the sample was 65 years old, and 54% was female. In total, 7% got dementia during a mean follow-up period of 6.6 years. Most individuals had an intermediate chronotype (56%), with about 20% of the individuals having a slightly early and late chronotype, and only about 3% having an extremely early and late chronotype. Individuals with a slightly early (HR, 1.26 [95% CI: 1.08, 1.46]) and an extremely late chronotype (HR, 1.42 [95% CI: 1.00, 2.02]) had an elevated risk of dementia. There were no significant interactions.

Having a slightly early as well as an extremely late chronotype was associated with an elevated risk of dementia.