The study included data from 21,475 people aged 15 or older who completed the American Time Use Survey between the years 2003 and 2006. The study examined the activities participants undertook two hours before and after bed time. It found that television viewing was by far and away the dominant pre-sleep activity, accounting for almost 50% of pre-bed time.

According to the authors of the study, Mathias Basner, MD, MS, MSc, and David F. Dinges, PhD, of the University of Pennsylvania School of Medicine in Philadelphia, they were surprised to find that watching television seemed to be the most important time cue for the beginning of the sleep period, rather than hours past sunset or other more biological factors. So, in fact, TV may make people stay up late, while alarm clocks make them get up early, potentially reducing sleep time below what is physiologically needed.

Sleeping less than 7-8 hours daily impairs alertness and is associated with increased obesity, morbidity and mortality. Despite this fact, up to 40 percent of Americans sleep for less than the recommended time per night.

"Given the relationship of short sleep duration to health risks, there is concern that many Americans are chronically under-sleeping due to lifestyle choices," said Dinges. Dr. Basner added that "According to our results, watching less television in the evening and postponing work start time in the morning appear to be the candidate behavioral changes for achieving additional sleep and reducing chronic sleep debt. While the timing of work may not be flexible, giving up some TV viewing in the evening should be possible to promote adequate sleep."

*The abstract, "The Time of Our Lives: Work, Sleep and Television" was presented on June 8.

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Materials provided by American Academy of Sleep Medicine. Note: Content may be edited for style and length.