Sleep duration and cognitive function : a systematic review

Abstract

Objective: To investigate the association of sleep duration with cognitive function in adults. Methods and Results: Relevant studies were searched through PubMed, ScienceDirect and Google Scholar using keywords of ((“cognitive” OR “cognition” OR “memory impairment”) AND (“sleep duration” OR “sleep hours” OR “sleep time”)). Studies on the association of sleep duration with cognitive function as measured by various cognitive assessment tools in adults aged 18+ years were included. The initiate search generates 415 articles, after excluding studies that were duplicates, not published in English journals and not conducted in adults, giving 10 to be included in this systematic review. These studies were conducted in 6 countries (US, China, France, Spain, England, and Finland) and most of them were cross-sectional studies (7 cross-sectional studies and 3 prospective studies). Most of the studies showed that participants with either long sleep duration (≥ 9 h per day) or short sleep duration (≤ 6 h per day) had higher risks of cognitive impairment than participants with sleep hours of about 7 hour per day. One study showed that short, but not long sleep duration was associated with poor cognitive function while four studies showed that only long sleep duration was associated with poor cognitive function. Some sleep-related factors such as sleep disorder breathing, excessive daytime sleepiness, sleep quality and sleep cycle may partly explain the association of sleep duration with cognitive functions. Conclusion: Most of the earlier studies consistently showed that both long (≥ 9 h per day) and short (≤ 6 h per day) sleep duration were associated with poor cognitive function. These findings provide evidence support for further intervention studies to examine the potential beneficial effect of normalizing sleep duration in preventing cognitive decline.