June 19, 2003 - Playing a video game or finishing up some work on computer before bed may keep you awake long after you turn the computer off. A new study shows that the bright light of a computer screen may alter the body's biological clock and suppress the natural production of melatonin that's critical to the normal sleep-wake cycle.

Melatonin is a hormone in the body that helps regulate a person's sleeping and waking hours. Researchers say exposure to light is thought to alter the amount of melatonin produced, and a decline in melatonin production is often blamed for sleep problems in the elderly.

In this study, published in the May issue of the Journal of Applied Physiology, researchers tested the effects of computer use at night on melatonin production as well as a variety of other factors known to affect a person's biological clock, such as body temperature and heart rate that are known to drop during sleep.

Seven healthy male computer users with an average age of 25 were told to wake up between 8 and 9 a.m. and go to bed between midnight and 1 a.m. for a week before the start of the experiment. They were then asked to perform either an exciting task (a video shooting game) or a boring task (simple math) using a computer with either a bright or dark display monitor on alternating nights between 11:30 p.m. and 2 a.m. before going to bed.

Researchers Shigekazu Higuchi and colleagues at the Akita University School of Medicine in Akita, Japan, found that melatonin production was significantly affected by the brightness of the computer screen as well as the type of task performed. Melatonin levels were lower after performing the exciting task in front of a bright display than in front of a darker one. But there was no difference in melatonin levels during the boring tasks.

Although the body temperature dropped at night under all conditions, working in front of a bright computer screen caused the computer user's body temperature to be significantly higher than when it was performed using a dimmer monitor.

Researchers say those results show that computer users who work or play at night in front of a bright display might lose sleep because performing an exciting task late at night may alter the normal nocturnal changes in melatonin and body temperature associated with a person's biological clock.