You're getting less sleep than you think, a study of 669 people in Chicago, shows.
Ask most folks, and they'll say they get less sleep than they like.
But if you then ask how long they sleep, they're likely to say they get more sleep than they really do.
That's what University of Chicago researcher Diane S. Lauderdale, PhD, and colleagues found when they strapped sensitive movement detectors to the wrists of 38- to 50-year-olds who volunteered for a long-term study of heart disease.
Based on the wristwatch-sized instruments -- and on detailed sleep logs kept by each study participant -- Lauderdale's team measured how long people slept, how long it took them to get to sleep, how much time they spent in bed, and how much of their time in bed they slept.
Averaging 6 hours and 42 minutes a night, white women slept longest -- but not as long as the seven hours they claimed to sleep on weeknights. They also got to sleep fastest (in about 13 minutes), spent the most time in bed (nearly eight hours), and slept most efficiently (85.7% of their time in bed).
Black men slept least: only 5 hours and 6 minutes a night. That was even less than the six hours they said they got on weeknights. They also took longest to fall asleep (about 36 minutes), spent the least time in bed (about seven hours), and slept least efficiently (73.2% of their time in bed).
These gender and racial differences persisted even when the researchers took various factors, such as income and employment, into account. However, lower income was associated with taking longer to get to sleep and lower sleep efficiency.
"People who make more money may have fewer worries, or they may have more control over their sleep environment," Lauderdale says.
Lauderdale and colleagues report their findings in the July issue of the American Journal of Epidemiology. Accompanying the study is an editorial by sleep expert Stuart F. Quan, MD, of the University of Arizona.
Sleep Deprivation in Blacks?
Quan notes that the sleep time and sleep efficiency Lauderdale saw in black Americans would merit a diagnosis of sleep deprivation.
But, "caution should be exercised before accepting these values as normative for all middle-aged African-Americans and Caucasians," he warns.
Lauderdale and colleagues agree with Quan that the sleep levels they found cannot be considered normal for all black Americans. However, they say they are the first to include a significant number of black Americans in a sleep study.
"We also agree that persons in northern metropolitan areas might sleep less than other persons," they write. "However, there are a great many people in such settings."
Bottom line: "People don't get enough sleep, and they get less sleep than they think," Lauderdale says, in a news release.
SOURCES: Lauderdale, D.S. American Journal of Epidemiology, July 2006; vol 164: pp. 5-16 and 19-20. Quan, S.F. American Journal of Epidemiology, July 2006; vol 164: pp. 17-18. News release, University of Chicago Medical Center.
By Daniel J. DeNoon
Reviewed by Louise Chang, M.D.
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