Sleep debt exacts deceptive cost

A modest but constant sleep shortage undermines alertness and other mental faculties in a matter of days, according to a report in the March 15 Sleep. Moreover, people who get by on a modest sleep deficit are often not aware of their shrinking thinking capabilities and don’t feel particularly drowsy, say Hans P.A. Van Dongen of the University of Pennsylvania School of Medicine in Philadelphia and his colleagues.

The results raise concerns about the effects of such “sleep debts” on military personnel, medical residents, and shift workers, the researchers say.

They studied 48 volunteers, ages 21 to 38, for 2 weeks. Participants were randomly assigned to 8, 6, or 4 hours nightly’ sleep, or no sleep at all for one 3-day period. Before the 2-week-long study, volunteers averaged 7 to 8 hours of nightly sleep.

Scores on tests of information monitoring and reaction times dropped for the 6-hour and 4-hour sleepers, but not the 8-hour sleepers. These losses, which were greater for 4-hour sleepers, mounted throughout the study. After 14 days, members of the 4- and 6-hour groups cited little sleepiness or difficulty thinking, but they displayed cognitive declines comparable to those in the entirely sleep deprived group 2 days into their 3-day ordeal.


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Bruce Bower has written about the behavioral sciences for Science News since 1984. He writes about psychology, anthropology, archaeology and mental health issues.