Sleep debt, also known as sleep deficit, describes the cumulative effect of a person not having sufficient sleep. It’s important for people to understand that a large sleep debt can well lead to physical and/or mental fatigue. The two known kinds of sleep debt are the results of total sleep deprivation and the results of partial sleep deprivation. Total sleep deprivation is when a person is kept awake for a minimum of 24 hours, while partial sleep deprivation occurs when either a person or lab animal has limited sleep for several days or even weeks. The specifics of sleep debt are still being debated by the scientific community; however, sleep debt is not considered to be a disorder.
It’s still being debated by researchers as to whether or not the concept of sleep debt is a measurable phenomenon. Duelling editorials are offered by two leading sleep researchers, Jim Horne and David F Dinges, in the September 2004 issue of the journal Sleep. Psychiatrists at the University of Pennsylvania School of Medicine conducted an experiment in 1977 which suggested that accumulative nocturnal sleep debt actually affects daytime sleepiness on the first, second, sixth, and seventh days of restricted sleep. In one particular study, subjects were tested using the PVT (Psychomotor Vigilance Task), where testing was done for a period of two weeks on different groups of people with different sleep times – this was done with four hours, six hours, eight hours, and total sleep deprivation. Every day the study group was tested on the PVT for the number of lapses. The results are interesting, showing that as time went by the performance of each group worsened, and that there was no obvious stopping point. It was found that moderate sleep deprivation was detrimental: the results of those who slept for six hours each night for a period of 10 days were similar to those who are completely sleep deprived for one day.
Sleep debt has been tested in a number of studies using the Sleep Onset Latency Test, which is a test designed to determine how quickly and easily a person can fall asleep. It’s known as a Multiple Sleep Latency Test when the test is done several times during a period of one day. In this test the subject is told to sleep, and is then awakened after determining how long it took the subject to fall asleep. Another useful tool for screening potential sleep debt is the Epworth Sleepiness Scale (ESS): this is a questionnaire with eight items, with scoring ranging between 0 and 24.
Another interesting study conducted in January 2007 at the Washington University in Saint Louis suggests that saliva testing of the enzyme amylase could be an indicator of sleep debt, because the activity of amylase increases in correlation with the length of time that the subject has been sleep deprived. Wakefulness can be controlled by the protein orexin, while important connections have been discovered between orexin, sleep debt, and amyloid beta. The suggestion here is that the development of Alzheimer’s could hypothetically be the result of excessive periods of wakefulness, or chronic sleep debt.
It’s been suggested that the demands of social activities, our work, plus the on-tap availability of the Internet and access to 24-hour home entertainment are the reasons why people tend to sleep less hours today than they did in days gone by. In fact, it was reported in 2007 by USA Today that most adults in America get approximately an hour less sleep time then the average sleep time 40 years ago.