A study of the sleep characteristics of 669 middle-aged adults found that people sleep much less than they should, and even less than they think. Published in the July issue in the American Journal of Epidemiology, the study also found that blacks sleep less than whites, men sleep less than women, and the poor sleep less than the wealthy.
Although participants spent an average of 7.5 hour a night in bed, they spent only 6.1 hours asleep. White women slept the most, 6.7 hours a night, followed by white men at 6.1 hours, black women at 5.9 hours and black men at 5.1 hours. Higher income also was associated with more sleep.
"People don't think they get enough sleep and they get less sleep than they think," said study author Diane Lauderdale, Ph.D., associate professor of health studies at the University of Chicago. "As we learn more and more about the importance of sleep for health, we find evidence that people seem to be sleeping less and less."
Studies suggest that average sleep times have declined since 1900, when people reported sleeping nine hours a night. Studies from the 1970s reported average sleep times closer to seven hours a night.
"Our study tells that we can't entirely trust those earlier surveys," Lauderdale said, "because people do not know how much they sleep."
This was one of the first large studies to combine sleep diaries with a technique called wrist actigraphy that uses a motion sensor -- worn like a watch -- to measure not just when people go to bed but when they fall asleep. Participants wore the device in the home for three days and nights. They also kept a log of their hours in bed.
Using the Actiwatch and nightly logs, Lauderdale and colleagues recorded how long people spent in bed (on average, 7.5 hours), how long it took them to fall asleep (22 minutes), how long they slept (6.1 hours), and their total sleep "efficiency" -- time asleep divided by tim
Contact: John Easton
University of Chicago Medical Center