We may be sleeping less than we think, says a study that found blacks sleep less than whites, men sleep less than women, and the poor sleep less than the wealthy!
The National Sleep Foundation (NSF) in US recommends at least eight hours of sleep for both men and women.
Researchers led by Diane Lauderdale of the department of health studies at University of Chicago found that people sleep much less than they should, and even less than they think, reported science portal EurekAlert.
They studied the sleep characteristics of 669 middle-aged adults using the Actiwatch - a watch that uses a motion sensor to measure when people fall asleep. They also kept a log of their hours in bed.
They recorded how long people spent in bed, how long it took them to fall asleep, how long they slept, and their total sleep "efficiency" -- time asleep divided by time in bed.
Although participants spent an average of 7.5 hours 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.
The study published in the July issue of the American Journal of Epidemiology also found the poor indeed sleep less than the wealthy.
"People who make more money may have fewer worries," Lauderdale suggested, "or they may have more control over their sleep environment."
Studies indicate 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.
Lack of sleep has long been connected with reduced ability to concentrate, decreased attention to detail and increased risk of motor vehicle accidents.
Recent studies have also linked chronic partial sleep deprivation to medical problems, including obesity, diabetes and hypertension.