Circadian syndrome (CircS) and cognitive trajectory deterioration in middle‐aged and older adults: A national cohort study with causal forest analysis

INTRODUCTION: Cognitive impairment is a global health challenge. Circadian syndrome (CircS) extends beyond metabolic syndrome to include sleep and mental health, but its long-term impact on cognitive trajectories remains unclear. METHODS: We analyzed 6218 participants from the China Health and Retirement Longitudinal Study (2011-2018). CircS was defined as ≥4 of 7 components. Cognitive trajectories were identified using latent class growth modeling. Associations were assessed via multinomial logistic regression, and heterogeneous effects via causal forest analysis. RESULTS: Three cognitive trajectories were identified: "persistently high" (40.29%), "persistently moderate" (43.78%), and "persistently low" (15.93%). CircS increased odds of "persistently low" global cognitive (adjusted OR = 1.27, 95%CI:1.06-1.52) and episodic memory (OR = 1.28, 95%CI:1.06-1.55) trajectories. Causal forest identified a vulnerable subgroup: younger age, mild anemia (Hb∼95 g/L), and elevated BMI. DISCUSSION: CircS is a significant, modifiable risk factor for adverse cognitive trajectories. Screening for CircS could enable early identification and targeted interventions, especially for the identified high-risk subgroup.