Many people think they can make-up for lost sleep during the work or school week by sleeping in on the weekend, however, a new study by researchers at Brigham and Women’s Hospital (BWH) and Rush University Medical Center finds that people may have a false sense of recovery from their sleep debt, and ultimately chronic sleep loss causes performance to deteriorate much more rapidly, particularly at night.
The research is published in the January 13, 2010 issue of Science Translational Medicine.
The research demonstrates how short-term and long-term sleep loss combine with the 24-hour circadian rhythm of a person’s internal clock to determine how well a person can perform at any moment. According to the study authors, during the afternoon and early evening, the circadian system has the remarkable capacity to override the negative effects of prior sleep loss. This combined with the short-term restorative properties of extended sleep can mask the effects of chronic sleep loss during a typical waking day.
However, the cumulative effect of chronic sleep loss causes performance to deteriorate much more rapidly for each consecutive hour spent awake, particularly during night. When individuals with a history of chronic sleep loss attempt to work extended hours into the night, their reaction times become 10 times slower, increasing the risk of accident and errors. In addition, the research found that chronic sleep loss made it more difficult to adjust to rotating shift schedules or jet lag.
“This paper continues a long line of systematic research on the effects of the brain’s 24-hour clock, sleep, and sleep deprivation. Through this process of discovery, not only are we unraveling the mysteries of normal and abnormal sleep and wakefulness, but we have crossed the threshold of being able to make evidence-based statements on the importance of protecting time for sleep in alertness-critical occupations,” said James Wyatt, PhD, study co-author and director, Sleep Disorders Service and Research Center at Rush University Medical Center.
The research involved nine healthy men who lived for three weeks on a schedule consisting of 43 hour “days,” each with 33 hours of scheduled wakefulness and 10 hours of scheduled sleep. This equates to 5.6 hour sleep opportunities every 24 hours. They were able to assess the effects of acute sleep loss from long consecutive hours awake, chronic sleep loss from reduced overall sleep over weeks, and the independent cycling of the circadian rhythm.
The study found that after waking from a 10-hour sleep, subjects’ performance was always good, but it deteriorated as each 33 hour waking day went on. As the chronic sleep debt increased, performance on reaction timing tests deteriorated at a faster rate for each hour spent awake.
When the body’s circadian rhythm was at the lowest-performing point in the late night/early morning, the reaction times were always slower, especially with acute sleep loss. When the circadian rhythm was at the highest-performing point in the late afternoon/early evening, reaction times were relatively normal despite substantial acute and chronic sleep loss.
“Many people have a false sense of reassurance that they can quickly recover from a chronic sleep debt with just one or two days of good sleep. Our work may help explain this: one long night of sleep can restore performance to normal levels for about six hours after waking, and the late afternoon and early evening alerting signal of the circadian rhythm can largely hide the effects of chronic sleep loss during the rest of a normal day,” said Daniel Cohen, lead author of the paper and a researcher in the division of Sleep Medicine at BWH, “However, the lingering effect of chronic sleep loss causes performance to deteriorate dramatically when these individuals stay awake for an extended period of time, for example when they try to pull an “all-nighter.”
Study authors say this research is of particular interest to those who work extended hours, and they hope it can be used to develop work schedules that reduce occupational errors, crashes and injuries.
“Individuals who get too little sleep during the work or school week but try to catch up on weekends may not realize that they are accumulating a chronic sleep debt.” said Elizabeth Klerman, senior author of the paper and an associate professor in the division of Sleep Medicine at BWH. “This may lead to a dangerous situation in which individuals do not realize the extent of their sleep deprivation and their vulnerability to sudden sleepiness when they try to drive or work late into the night.”
This work was supported by the U.S. Air Force Office of Scientific Research, the National Institutes of Health, and the National Space Biomedical Research Institute.