June 8 (HealthDay News) -- Many generations ago, a dark night sky and fatigue probably signaled it was time to go to sleep.
Today, Conan O'Brien, Jon Stewart and the Desperate Housewives are more influential in determining bedtimes -- and it may be contributing to many Americans' chronic sleep deprivation, a new study says.
In the study, researchers looked at data about the sleep habits and bedtime rituals of 21,475 participants aged 15 or older who completed the American Time Use Survey between 2003 and 2006.
In the two hours around bedtime, TV viewing was the most common activity, accounting for almost 50 percent of the activities undertaken in the time before bed, according to the study to be presented Monday at the Associated Professional Sleep Societies annual meeting, in Seattle.
The finding means that TV -- rather than hours past sunset or biological signs -- has become the most important signal for sleep.
And staying up to catch the end of a favorite show may make people stay up later than they otherwise would. In the morning, their alarm clocks may jar them awake earlier than they would naturally awaken.
These facets of modern life are potentially reducing sleep time below what is physiologically required, the researchers noted in a news release from the American Academy of Sleep Medicine.
"Given the relationship of short sleep duration to health risks, there is concern that many Americans are chronically under-sleeping due to lifestyle choices," study co-author David Dinges, of the University of Pennsylvania School of Medicine in Philadelphia, said in the news release.
Americans should watch less late-night TV and go to work later in the morning, the researchers suggested.
"While the timing of work may not be flexible, giving up some TV viewing in the evening should be possible to promote adequate sleep," said study co-author Dr. Mathias Basner.
Getting less than seven to eight hours of sleep daily can lead to impaired alertness and has been linked to higher rates of obesity, illness and death. Even so, up to 40 percent of Americans are not getting the recommended amount of sleep at night, according to the news release.
SOURCE: American Academy of Sleep Medicine, news release, June 8, 2009