Chronotype as a Potential Risk Factor for Cognitive Decline: The Mediating Role of Sleep Quality and Health Behaviours in a 10-year Follow-Up Study

Background – With rising life expectancies and ageing populations worldwide, preserving cognitive health is an urgent global priority. Chronotype could be a potential risk factor for cognitive decline, either directly through mediators such as sleep quality, alcohol intake, physical inactivity, and smoking. 
Methods - This study used data from individuals aged 40 years and older the Lifelines cohort study (n=23,798). Chronotype was assessed with the Munich ChronoType Questionnaire, included as a continuous score of mid-point sleep corrected for sleep debt on work-days. Multiple linear regression examined the association between chronotype and cognitive decline, including moderation by age, educational attainment, and sex. The KHB-method was applied to test mediation by sleep quality, alcohol intake, physical activity, and smoking. 
Outcomes – Non-verbal fluency and executive functioning assessed with the Ruff Figural Fluency Test (RFFT). Cognitive decline was calculated by subtracting the RFFT sum score at 10-year follow-up from the score at baseline. 
Results – Educational attainment, but not age or sex, moderated the relationship with chronotype. No significant effects were observed in the low (0·07, 95% CI: -0·44, 0·57) or middle (0·41, 95% CI: -0·88, 0·06) education groups. In the high-education group, however, each one-hour increase in chronotype corresponded to a 0·80-point decline per decade (95% CI: -1·34, -0·26). In the latter group, sleep quality and current smoking mediated 13·52% and 18·64% of the association, respectively. 
Interpretation - Chronotype was associated with cognitive decline in individuals with higher education, highlighting the importance of targeted prevention strategies.
Funding – This work is funded by the Dutch Medical Research Council (grant number:1051003210005).