Association between longitudinal trajectories of insomnia symptoms and subsequent cognitive decline: a prospective cohort study

BACKGROUND: Previous studies found that insomnia was an important risk factor for cognitive decline. However, previous studies only focused on baseline insomnia status, not taking into consideration the changes in insomnia status during follow-up. The study aimed to investigate the association between longitudinal trajectories of insomnia symptoms and subsequent cognitive decline. METHODS: Data were from 7727 adults aged ≥50 in the Health and Retirement Study. The exposure variable was insomnia symptoms, including difficulties in initiating and maintaining sleep, early morning awakening and non-restorative sleep. Insomnia status was assessed biennially from 2002 to 2006, and its change patterns were categorised as low, decreasing, increasing and high trajectory. Linear mixed effects models were used to evaluate the associations between trajectories of insomnia symptoms and consequent cognitive decline. FINDINGS: Compared with participants experiencing sustained low insomnia symptoms, those experiencing decreasing insomnia symptoms (β = -0.013; 95% CI, -0.020 to -0.006), increasing insomnia symptoms (β = -0.018; 95% CI, -0.031 to -0.006) and sustained high insomnia symptoms (β = -0.025; 95% CI, -0.037 to -0.014) showed significantly accelerated global cognitive decline. In contrast, compared with participants experiencing sustained high insomnia symptoms, those with decreasing insomnia symptoms were significantly associated with decelerated global cognitive decline. CONCLUSION: Sustained high insomnia symptoms accelerates cognitive decline, while recovery of insomnia symptoms decelerates cognitive decline.