Sleep, Performance, and Public Safety

Costly, Preventable Accidents

Insufficient sleep may not have led the news in reporting on serious accidents in recent decades. However, that doesn't mean fatigue and inattention due to sleep loss didn't play a role in these disasters. For example, investigators have ruled that sleep deprivation was a significant factor in the 1979 nuclear accident at Three Mile Island, as well as the 1986 nuclear meltdown at Chernobyl.  Investigations of the grounding of the Exxon Valdez oil tanker, as well as the explosion of the space shuttle Challenger, have concluded that sleep deprivation also played a critical role in these accidents. In both cases, those in charge of the operations and required to make critical decisions were operating under extreme sleep deprivation. While the Challenger disaster put the multi-billion dollar shuttle program in peril, the Exxon Valdez oil spill resulted in incalculable ecological, environmental, and economic damage.

In addition to the ties between such high-profile disasters and sleep deprivation, there is a growing recognition of the link between lack of sleep and medical errors in our hospitals. According to the Institutes of Medicine, over one million injuries and between 50,000 and 100,000 deaths each year result from preventable medical errors, and many of these may be the result of insufficient sleep, Doctors, especially newly graduated interns, are often expected to work continuous shifts of 24 to 36 hours with little or no opportunity for sleep. Although it is difficult to estimate the extent that sleep deprivation plays in medical errors, studies have shown a significant impact. For example, a 2004 study led by Dr. Charles Czeisler of the Division of Sleep Medicine at Harvard Medical School found that hospitals could reduce the number of medical errors by as much as 36 percent by limiting an individual doctor's work shifts to 16 hours and reducing the total work schedule to no more than 80 hours per week. Long shifts and other factors that result in sleep loss have safety consequences for our highways as well. A National Sleep Foundation survey has revealed that 60 percent of adult drivers—about 168 million people—say they have driven a vehicle while feeling drowsy in the past year, and that more than one-third (103 million people) have actually fallen asleep at the wheel. Unfortunately, many of these situations end in tragedy. The National Highway Traffic Safety Administration estimates that 100,000 police-reported crashes are the direct result of driver fatigue each year, and they consider this a conservative estimate. More recent data suggests that the true number is likely much higher. The Institute of Medicine estimates—based on recent high quality naturalistic and epidemiologic studies—that drowsy driving is responsible for fully 20 percent of all motor vehicle crashes. That would mean that drowsy driving causes approximately 1 million crashes, 500,000 injuries, and 8,000 deaths each year in the U.S.

How Sleep Deprivation Affects Mental Performance

The earliest scientific evidence of a link between sleep and performance dates back to the early 1930's, when Nathaniel Kleitman, one of most significant figures in the field of sleep medicine, discovered a daily pattern in the speed and accuracy of cognitive performance. He showed that even in well-rested individuals there was a decrease in the level of individual performance that occurred in the early morning and again late at night. Thus, even when we are getting the amount of sleep we need, we can still expect normal fluctuations in our ability to function.  In addition to these normal fluctuations, not getting enough sleep—whether for just one night or over the course of weeks to months—has a significant effect on our ability to function. Sleep deprivation negatively impacts our mood, our ability to focus, and our ability to access higher-level cognitive functions. The combination of these factors is what we generally refer to as mental performance. In the laboratory, researchers use scientific studies to determine just how significantly varying levels of sleep disturbance impact various types of mental performance.

The most immediate effect of sleep deprivation is sleepiness. In our daily lives, we may experience this as a general fatigue, lack of motivation, or even the experience of nodding off. In the research or clinical setting, scientists measure sleepiness using a variety of methods. After a period of sleep deprivation, there are noticeable changes in brain activity, as measured by an electroencephalogram (EEG). These changes correspond to a lower level of alertness and a general propensity to sleep. Any period of continual wakefulness beyond the typical 16 hours or so will generally lead to these measurable changes.

In addition to the feeling of sleepiness and changes in brain activity that accompany a night without sleep, other measures of performance are noticeably altered. Concentration, working memory, mathematical capacity, and logical reasoning are all aspects of cognitive function compromised by sleep deprivation. However, not all of these functions rely on the same regions of the brain, nor are they impacted by sleep deprivation to the same degree. For example, the region of the brain known as the prefrontal cortex (PFC) is responsible for many higher-level cognitive functions and is particularly vulnerable to a lack of sleep. As a result, people who are sleep deprived will begin to show deficits in many tasks that require logical reasoning or complex thought.

Determining just how much performance is affected by sleep loss is difficult, in part because of factors such as individual differences in sensitivity to sleep deprivation, as well as individual differences in motivation to stay alert despite sleep loss. Even so, the evidence is clear that a lack of sleep leads to poor performance. As the prevalence of inadequate sleep grows and the demands of the workplace change, it becomes increasingly critical that we recognize and take action to mitigate the impact that insufficient sleep has on our safety and well-being.