In a study on the effects of sleep deprivation, investigators at the University of Pennsylvania found that subjects who slept four to six hours a night for fourteen consecutive nights showed significant deficits in cognitive performance equivalent to going without sleep for up to three days in a row. Yet these subjects reported feeling only slightly sleepy and were unaware of how impaired they were. The research article, "The Cumulative Cost of Additional Wakefulness: Dose-Response Effects on Neurobehavioral Functions and Sleep Physiology From Chronic Sleep Restriction and Total Sleep Deprivation," appears in the March issue of the journal 'SLEEP'.
According to Principal Investigator David Dinges, "This is
the first systematic study to look at the prolonged
cognitive effects of chronic sleep restriction lasting for
more than a week. The results provide a clearer picture of
possible dangers to people who typically are awake longer
on a regular basis," he explained, "including members of
the military, medical and surgical residents, and shift
workers. Reduced cognitive abilities can occur even with a
moderate reduction in sleep."
Cognitive performance deficits included reduced ability to
pay attention and react to a stimulus, such as when
driving, or monitoring at airports. Other deficits involved
impairment of the ability to think quickly and not make
mistakes, and a reduced ability to multi-task -- to hold
thoughts in the brain in some order while doing something
else.
Dr. Patricia A. Grady, Director of the National Institute
of Nursing Research, NIH, which provided primary funding
for the study, said, "These findings show that while young
adults may believe they can adapt to less than a full
night's sleep over time, chronic sleep deprivation may
seriously affect their performance while they are awake,
and they may not even realize it."
Investigators also found that to prevent neurobehavioral
defects from accumulating, the average person needs 8.16
hours of sleep during a 24-hour day, although there were
differences among individuals in their need for sleep.
The study included 48 healthy individuals aged 21 to 38 who
were divided into four groups -- those who were allowed to
sleep up to either 8, 6 or 4 hours per night during a 24-
hour period for two weeks, and those who were deprived of
sleep for three consecutive 24-hour periods. The
experiments were conducted in a lab with constant
monitoring. When awake, participants could watch movies,
read, and interact with lab staff but could not have
caffeine, alcohol, tobacco or medications.
In addition to NINR, other NIH funding was provided by the
National Center for Research Resources and National Heart,
Lung and Blood Institute. NIH is part of the Department of
Health and Human Services. A grant from the Air Force
Office of Scientific Research supported total sleep
deprivation data used in the study.
National Institute of Nursing Research (NINR)
http://www.nih.gov/ninr/