For years people have believed that getting too little sleep can make people sick. Yet, scientists have not been able to show how sleeping affects human health. Now studies are beginning to provide answers. Experiments show that the body defense system is somehow repaired or strengthened during sleep. And they seem to show that the defense system itself helps control how much a person sleeps. Researchers divide sleep into two different periods. One is called rapid eye movement or REM (rapid eye movement) sleep. In this period, the person dreams and the eyes move quickly behind the closed eyelids. The other period is longer. It is called non-REM sleep. Researchers do not understand either one very well. They think, however, that REM sleep serves some feeling purposes for the brain. They do not exactly know the purpose of non-REM sleep, but the new studies are trying to explain it.
Not long ago, an experiment looked at the effect of the lack of sleep on rats. Rats die if they are not permitted to sleep for several weeks, but rats who died during the sleep experiments seemed normal when researchers later tested their organs. Carol Abelson of the National Institute of Mental Health found that the rats died of a blood infection caused by bacteria. The bacteria were kinds that normally do not cause disease. She also found that the infection did not damage body tissue. Dr. Abelson says this seems to show that the lack of sleep made the rats' defense systems unable to attack the bacteria.
Another study looked at healthy people and sleep loss. David Digges at the University of Pennsy1vania studied 24 healthy people who agreed to live in a laboratory and remain awake for one week. The researchers expected to find low defense system activity after sleep loss, but instead, they found increased activity in cells that attacked bacteria and viruses. After one week without sleep the body seemed to be developing a defense against an unknown attacker. Scientists also question how the defense system is involved in normal sleep. One answer is that defense system cells are involved in producing sleep factors. James Kugel of the University of Tennessee says sleep factors increase during the day and make people feel the need for sleep at night. The sleep factors can come from many parts of the body.
Recently, Dr. Kugel helped find one sleep factor. It is in the human intestines. During the day, a kind of defense system cells eat intestinal bacteria and release tiny proteins from the cell walls of the bacteria. These proteins move throughout the body. They may reach the brain. When they are placed in animal brains, the animals fall into a long deep sleep.
Scientists say that sleep research may help answer many questions. For example, they explain the cause of chronic fatigue syndrome, in which a person always feels tired. This could also help people with AIDS. AIDS patients feel tired during the day. The reason may be that their damaged defense systems interfere with normal sleep.