The study analyzed data from eight time-use surveys. The earliest survey was conducted in 1975. The most recent data came from the 2006 American Time Use Survey.
Surveys were completed by more than 73,000 adults. They were at least 18 years of age. “Short sleep” was defined as less than six hours of sleep, nap or rest in a 24-hour period.
Results show that the overall odds of being a short sleeper have not increased over the past 31 years. The highest proportion of short sleepers was 11.8 percent in the 1998-99 survey. The lowest proportion was 7.5 percent in the 1992-94 survey. The proportion was 9.3 percent in the 2006 survey.
“The assertion that sleep durations have declined drastically in the U.S. population in general over the past 30 years may be inaccurate,” wrote the authors.
But the study did find a significant trend for full-time workers. Their odds ratio for short sleep was increased by 19 percent.
“Longer work times seem to be the most important cofactor for short sleep,” the authors concluded.
Unmarried adults, those with some college education, and African Americans also had higher odds of short sleep. Women, older adults, Asians, Hispanics and married people were less likely to be short sleepers.
The authors noted that the 24-hour time-use surveys split the sleep period. They combined the end of one night of sleep with the beginning of the second night of sleep. Daytime sleep also was added to the total.
And time categorized as “sleep” included activities such as “resting” and “getting up.” Thus the time-use surveys may have overestimated true sleep time.
Dr. Mathias Basner wrote a commentary on the study in the same issue of Sleep. He noted that chronic, partial sleep deprivation remains an important public health issue.
Why do millions of Americans put their health at risk by failing to get enough sleep? One reason may be that short sleepers simply adjust to regular sleep loss.
“Those who do need more sleep simply may have habituated to feeling sleepy,” Basner wrote. “Many of the short sleepers may have ‘forgotten’ how well they could feel and perform if they satisfied their individual sleep need.”