Association of postlunch napping duration and night-time sleep duration with cognitive impairment in Chinese elderly: a cross-sectional study.

Objective: To analyse the independent and combined associations of postlunch napping duration and night-time sleep duration with risk of cognitive impairment among Chinese elderly.

Design: A cross-sectional study.

Setting: We analysed the data from Zhejiang Ageing and Health Cohort, a population-based survey of seven counties located in Zhejiang province in eastern China.

Participants: 10 740 participants aged 60 years or older were included in final analysis.

Primary And Secondary Outcome Measures: Cognitive impairment was assessed through Mini-Mental State Examination. Data on sleep-related characteristics was collected in the behavioural habits section within the questionnaire.

Results: Relative to participants with 1-30 min of postlunch napping, those who did not nap and who napped longer had significantly higher risks for cognitive impairment. OR of cognitive impairment were 1.41 (95% CI 1.14 to 1.75) for participants with longer night-time sleep duration (≥9 hours), compared with those sleeping 7-8.9 hours. In addition, combined effects were further identified. Participants with both longer night-time sleep duration (≥9 hours) and longer postlunch napping duration (>60 min) (OR=2.01, 95% CI 1.30 to 3.13), as well as those with both longer night-time sleep duration (≥9 hours) and appropriate postlunch napping duration (1-30 min) (OR=2.01, 95% CI 1.20 to 3.38), showed significantly higher risk of cognitive impairment than those with sleeping 7-8 hours and napping 1-30 min. Meanwhile, a 34% increase in odds of cognitive impairment was observed in participants with both shorter night-time sleep duration (5-6.9 hours) and no napping.

Conclusion: Both postlunch napping duration and night-time sleep duration were independently and jointly associated with cognitive impairment, which needs verification in prospective studies.