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 of the American Journal of Epidemiology, the study also found that African Americans 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 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. Higher income also was associated with more sleep.

Studies suggest that average sleep times have declined since 1900, when people reported sleeping 9 hours a night. Studies from the 1970s reported average sleep times closer to 7 hours a night.

“Our study tells that we can’t entirely trust those earlier surveys because people do not know how much they sleep,” said study author Diane Lauderdale, PhD, associate professor of health studies at the University of Chicago.

In the study, the researchers combined sleep diaries with wrist actigraphy, which 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 their homes for 3 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 time in bed (81%). Below is a chart summarizing the author’s findings:
 

	All	White women	White men	Black women	Black men
Time in bed (hours)	7.51	7.84	7.34	7.55	7.10
Sleep latency (minutes)	22.33	13.30	18.52	28.36	35.93
Sleep duration (hours)	6.13	6.71	6.09	5.90	5.10
Sleep efficiency	80.8%	85.7%	82.4%	78.2%	73.2%

They found that sleep duration and sleep efficiency were “remarkably lower” than values reported in most previous studies, noted Stuart F. Quan of the University of Arizona in a commentary. The researchers were particularly surprised by the short span and poor quality of sleep among African-American men―5.1 hours a night and 73% sleep efficiency.

“Although sleep scientists have generally accepted that the average sleep duration of Americans has been declining in parallel with our transformation to a frenetic 24-hour society,” Quan wrote, “most sleep clinicians would consider those values indicative of sleep deprivation even by current standards.”

Lack of sleep has long been connected with reduced ability to concentrate, trouble learning, decreased attention to detail, and increased risk of motor vehicle accidents. More recent studies have tied chronic partial sleep deprivation to medical problems, including obesity, diabetes, and hypertension.

To submit stories for the Sleep Report enewsletter, email lkauffman@ascendmedia.com

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