Washington, June 8 : Watching television before bedtime may contribute to chronic sleep debt, according to a new study.

For the study, researchers included data from 21,475 people aged 15 or older who completed the American Time Use Survey between the years 2003 and 2006.

They studied the activities participants undertook two hours before and after bed time.

The authors found that television viewing was by far and away the dominant pre-sleep activity, accounting for almost 50 percent of pre-bed time.

Study authors Mathias Basner, MD, MS, MSc, and David F. Dinges, PhD, of the University of Pennsylvania School of Medicine in Philadelphia, 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.

The study has been presented at SLEEP 2009, the 23rd Annual Meeting of the Associated Professional Sleep Societies. (ANI)