Background: Mount evidence from observational studies suggested that associations between sleep duration and the risks of mild cognitive impairment (MCI)/dementia or cognitive decline had been recognized.
Methods: To explore the precise and continuous effect of sleep duration on these risks, we conducted a dose-response meta-analysis to quantitatively assess it.
Results: Five prospective cohort studies and 4 cross-sectional studies were eligible for inclusion criteria, which involved 62937 individuals, and documented 2718 MCI/dementia cases and 5596 cognitive decline cases. The pooled RR per 1 h increases in sleep duration was 0.99 (95% CI 0.97-1.01, I2 = 62.40%, P = 0.02, n = 6) for cognitive decline risk, and 0.98 (95% CI 0.97-1.00, I2 = 0%, P = 0.42, n = 4) for MCI/dementia risk. Similar U-shaped non-linear relationship of sleep duration and the risks of MCI/dementia and cognitive decline was revealed, respectively (all Pnon-linearity < 0.001), whose peaks are approximately 7 h.
Conclusion: In conclusion, 7 h sleep duration tends to acquire the least risk of MCI/dementia or cognitive decline; however, more well-designed randomized controlled trials are urgently needed to balance potential modifiers.
Keywords: Cognitive decline; Dementia; Dose–response; Meta-analysis; Mild cognitive impairment (MCI); Sleep duration.