A 6-8-Hour Nighttime Sleep Strategy and Subsequent Cognitive Performance: A Target Trial Emulation Study

Sleep duration is a modifiable factor linked to cognitive aging among middle-aged and older adults, but existing evidence is largely correlational. Using observational data in which sleep duration was self-reported, we emulated a target trial to estimate the effect of maintaining a 6-8 h nighttime sleep strategy on subsequent cognitive performance.

This target trial emulation study analyzed participants from the China Health and Retirement Longitudinal Study (CHARLS), a longitudinal, nationally representative prospective cohort of Chinese adults aged 45 years and older, and followed them from 2011 to 2020. Nocturnal sleep duration was self-reported at every wave. The 6-8 h sleep strategy was compared with a non-6-8 h strategy (<6h or >8h) using intention-to-treat (ITT), per-protocol (PP), and inverse probability of censoring weighting (IPCW)-weighted PP analyses. Primary outcome was the total cognitive score (range 0-21) after 9 years. Groups were balanced by 1:1 propensity-score matching (PSM) on 18 baseline covariates, and missing baseline covariate data were handled by multiple imputation by chained equations.

Of 8147 eligible participants, 2341 matched pairs were included after PSM. The 6-8 h sleep strategy was consistently associated with higher cognitive scores than the non-6-8 h strategy in the ITT analysis (β = 0.237, 95% CI 0.016 to 0.458, p=0.036), the unweighted PP analysis (β = 0.394, 95% CI -0.013 to 0.801, p=0.058), and the IPCW-weighted PP analysis (β = 0.614, 95% CI 0.176 to 1.052, p=0.006). All estimates were modest in absolute terms, corresponding to 5.3% and 13.7% of one standard deviation of the outcome for the ITT and weighted PP analyses. The dose-response curve showed a nonlinear, inverted U-shaped association (P for non-linearity <0.001), with the highest predicted cognition at about 6.7 h of sleep. Neither sex nor age modified the association (P for interaction 0.84 and 0.27).

By emulating a target trial with repeated prospective cohort data, this study moves beyond simple association and suggests that maintaining 6-8 h of self-reported nighttime sleep is associated with modestly higher subsequent cognitive performance. Target trial emulation improves the rigour of effect estimation but does not eliminate residual confounding, exposure misclassification or selective attrition; the findings require confirmation in studies using objective sleep assessment and more complete control of time-varying confounding.