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Penn Study Finds People Respond Poorly Despite Feeling only 'Slightly' Tired

(Philadelphia, PA) -- Sleep: Don't be too sure you're getting enough of it.

Those who believe they can function well on six or fewer hours of sleep every night may be accumulating a "sleep debt" that cuts into their normal cognitive abilities, according to research conducted at the University of Pennsylvania School of Medicine. What's more, the research indicates, those people may be too sleep-deprived to know it.

The study, published in the March 15 issue of the journal Sleep, found that chronically sleep-deprived individuals reported feeling "only slightly sleepy" even when their performance was at its worst during standard psychological testing. The results provide scientific insight into the daily challenges that confront military personnel, residents and on-call doctors and surgeons, shift workers, parents of young children, and others who routinely get fewer than six hours of sleep each night.

"Routine nightly sleep for fewer than six hours results in cognitive performance deficits, even if we feel we have adapted to it," said Hans P.A. Van Dongen, PhD, Assistant Professor of Sleep and Chronobiology in Penn's Department of Psychiatry and corresponding author of the study. "This work demonstrates the importance of sleep as a necessity for health and well-being. Even relatively moderate sleep restriction, if it is sustained night after night, can seriously impair our neurobiological functioning."

David F. Dinges, PhD, Professor of Psychology in the Department of Psychiatry and Chief of the Division of Sleep and Chronobiology, served as principal investigator for the study.

Dinges, Van Dongen and their colleagues looked at the effects of four hours nightly sleep and six hours nightly sleep on healthy volunteer subjects aged 21 to 38, over a two-week period. They compared the results of the subjects' accumulating performance deficits, determined by standard psychomotor vigilance and other cognitive tests, with similar test results obtained from subjects who had gone without sleep for more than three nights.

The first group of subjects experienced increasing lapses in psychomotor vigilance over days, resulting in a decline of performance that matched that of the subjects who went without sleep for 88 hours. At that level, the subjects suffered lapses in their ability to react that would put them at risk driving or flying an airplane. They were also less able to multi-task successfully.
"The physiologic expression of sleep in humans appears to have multiple functions, ranging from the metabolic to the neurocognitive," Van Dongen said.

Other scientists who worked on the study are Greg Maislin, MS, MA, also of Penn, and Janet M. Mullington, PhD, of Beth Israel Deaconess Medical Center and Harvard University.

The study was funded by the National Institute of Nursing Research of the National Institutes of Health with additional financial assistance from the National Center for Research Resources and the National Heart, Lung and Blood Institute.


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Penn Medicine is one of the world's leading academic medical centers, dedicated to the related missions of medical education, biomedical research, and excellence in patient care. Penn Medicine consists of the Raymond and Ruth Perelman School of Medicine at the University of Pennsylvania (founded in 1765 as the nation's first medical school) and the University of Pennsylvania Health System, which together form a $5.3 billion enterprise.

The Perelman School of Medicine has been ranked among the top five medical schools in the United States for the past 18 years, according to U.S. News & World Report's survey of research-oriented medical schools. The School is consistently among the nation's top recipients of funding from the National Institutes of Health, with $373 million awarded in the 2015 fiscal year.

The University of Pennsylvania Health System's patient care facilities include: The Hospital of the University of Pennsylvania and Penn Presbyterian Medical Center -- which are recognized as one of the nation's top "Honor Roll" hospitals by U.S. News & World Report -- Chester County Hospital; Lancaster General Health; Penn Wissahickon Hospice; and Pennsylvania Hospital -- the nation's first hospital, founded in 1751. Additional affiliated inpatient care facilities and services throughout the Philadelphia region include Chestnut Hill Hospital and Good Shepherd Penn Partners, a partnership between Good Shepherd Rehabilitation Network and Penn Medicine.

Penn Medicine is committed to improving lives and health through a variety of community-based programs and activities. In fiscal year 2015, Penn Medicine provided $253.3 million to benefit our community.

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