Impact of one night of sleep restriction on sleepiness and cognitive function: A systematic review and meta-analysis

Sleep is essential for maintaining optimal psychological and physical health, yet many people often find themselves sacrificing sleep due to busy schedules or other demands. In a recent meta-analysis of 44 studies, Larissa Wüst and colleagues from the Center for Chronobiology in Basel, found that one night of reduced sleep duration already affects sleepiness and cognitive function in healthy adults.

The meta-analysis included data from over 1,000 participants and compared the effects of one night of sleep restriction—where participants averaged around 4 hours of sleep—to a normal sleep condition, where participants slept around 8 hours. One key requirement for the included studies was a sleep duration difference of at least two hours between the restricted and normal sleep conditions.

The results showed a significant decrease in subjective alertness following sleep restriction. Participants reported feeling sleepier, as measured with the Karolinska Sleepiness Scale or the Stanford Sleepiness Scale. Sustained attention, which is often interpreted as an objective indicator of alertness, was significantly impaired after one night of sleep restriction, as indicated by longer reaction times and a higher number of attentional lapses after sleep restriction. Sustained attention is crucial for several activities, such as driving and monitoring tasks.

Interestingly, not all cognitive functions were equally affected. The analysis found that more complex cognitive tasks including, assessing working memory (tasks that involve holding and manipulating information), inhibitory control (tasks that require managing impulses and distractions), and cognitive throughput (how many pieces of information can be processed within a given time) did not show significant declines after one night of sleep restriction. However, it’s important to note that fewer studies investigated these more complex cognitive tasks, so more research is needed to draw firm conclusions.

Overall, the findings from this meta-analysis emphasize that even a single night of restricted sleep can reduce both subjective and objective alertness, while more complex cognitive tasks may remain unaffected in the short term. These results are particularly relevant for understanding how sleep loss can impact everyday activities that require sustained attention, such as driving.