Is lack of sleep a problem in your home?

If lack of sleep is a problem in your family, blame Thomas Edison. Before the invention of electricity, our sources of light were expensive and inefficient, so the whole family was in bed shortly after sunset. Today we pay bills online at 11 p.m. and our kids are instant-messaging their friends because they're just finishing their homework or walking in from hockey practice.

"A lot of families don't see getting a good night's sleep as a health habit in the same way they see eating well, wearing sunscreen or not smoking," says Dr. Judith Owens, director of the pediatric sleep disorders clinic at Hasbro Children's Hospital in Providence, R.I.

Sleep scientists have studied the damaging effects of insufficient sleep in adults for many years. In fact, studies of the Three Mile Island and Challenger space shuttle disasters, as well as thousands of vehicle accidents every year, reveal lost sleep as the culprit. But researchers have only recently turned their attention to children.

One study turned up a startling find: for each of the past three decades, children have lost a half-hour of sleep. Today's kids sleep an average of 90 minutes less each night than their counterparts did 30 years ago. Projecting that pattern forward is frightening, especially since the effect of sleep loss on growing minds and bodies is still not well understood.

Scientists know that children's sleep is different from that of adults in one important way: children spend much more time in rapid eye movement (REM) sleep, which is the "dream" stage of the sleep cycle. Infants, who typically sleep up to 16 hours a day, spend half that time in REM sleep; compare that with a young adult, who spends about 90 minutes in REM sleep, or a 60-year-old, who spends only 20 minutes in the dream stage.

REM sleep is a crucial time for brain activity. The brain is at least as active during the dream cycle as it is when a person is awake. Scientists assume all this activity is related to neural plasticity, the growth and change of brain cells. Recent research on children's brain development shows that kids aren't born with complete brains; instead, they have a "starter set" that expands and contracts according to experience.

Scientists believe REM sleep provides the opportunity for this growth and change. It's during this time that kids' brains process the information they encounter during the day that's why they spend so much more time in this stage of sleep. Because the length of the REM cycle increases as the night wears on, a shortened night of sleep means less time spent in REM sleep. Less time in REM sleep, in turn, means less time for this important brain activity.

In theory, less time for brain growth and development means that the brain can't change and modify itself as it needs to. This affects the brain's ability to react and perform during the day. Recent studies on children's sleep support this idea. In an American study of kids aged 10 to 14, researchers limited their sleep to just five hours. The next day, both their abstract thinking and their creativity (as measured with standardized tests) had decreased temporarily.

One study of nine- to 12-year-old Israeli children, subtitled "What a Difference an Hour Makes," intended to address the just-one-more-TV-show problem. The study, released earlier this year, showed that reducing a child's sleep by a single hour negatively affected his memory and reaction time on standardized tests, says Avi Sadeh, an associate professor in the department of psychology at Tel Aviv University and author of the study.