Can a week of unrestricted sleep make up for long-term sleep loss?

Seven days of unrestricted sleep following prolonged sleep restriction did not fully restore cognitive performance, locomotor activity, and neurophysiological measures in healthy young people.

This Study Summary was published on October 3, 2021.


According to a 2014 CDC survey, 35% of U.S. adults sleep less than 7 hours per night. These short sleepers are more likely to smoke, to be physically inactive, to have suffered a stroke or heart attack, and to suffer from arthritis, asthma, cancer, chronic kidney disease, chronic obstructive pulmonary disease, coronary artery disease, depression, diabetes, or obesity.

Sleep loss can also worsen alertness, attention, cognitive performance, and memory. Many people experience sleep loss at some point, so this study sought to understand how the human brain recovers from long periods of sleep restriction.

The study

In this 21-day nonrandomized, noncontrolled trial, 4 days of unrestricted sleep were followed by 10 days of restriction and 7 days of recovery. Data from 13 of the 23 participants (12 women and 1 man, healthy, aged 21.5 on average) were used in the final analysis.

Sleepiness (as measured via the Karolinska Sleepiness Scale[1]), cognitive performance (reaction time and accuracy from a Stroop task), brain activity (measured via EEG), and locomotor activity (measured via actigraphy) were assessed daily.

The results

The average baseline sleep time was 7 hours 37 minutes; the average restricted sleep time was 5 hours 18 minutes (baseline − 30%); and the average recovery sleep time was 7 hours 36 minutes. The average sleepiness scores were 3.4 at baseline (alert), 5.55 during sleep restriction (not alert but not sleepy), and 3.25 during recovery.

With regard to the Stroop task, time to completion (a measure of reaction time) was 24.3 minutes at baseline, 37.5 minutes during sleep restriction, and 21.6 minutes during recovery, whereas response accuracy was lower during sleep restriction (−1.96%) and recovery (−1.64%) than at baseline.

Locomotor activity was increased and brain activity disrupted during sleep restriction, compared to baseline, with only partial recovery during the sleep recovery period.

The big picture: How much sleep is needed to recover from sleep deprivation? Several other studies have tried to find the answer.

In a 2020 randomized trial, 1 night of total sleep deprivation followed by 2 nights of sleep recovery (12 and 8 hours) restored hippocampal connectivity but not memory performance.[2]

A 2016 trial comparing the participants’ optimal sleep duration to their habitual sleep duration found that individuals who routinely underslept by an hour may need up to 9 days of unrestricted sleep to recover.[3]

A 2003 trial explored the dose-response of chronic sleep deprivation. It found that even moderate sleep loss could impair neurobehavioral function.[4]

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This Study Summary was published on October 3, 2021.