Why Do We Sleep?

What does sleep do for us? While it may seem like a rhetorical question, it's not. Scientists know we need sleep, but they don't know exactly what happens to our bodies and our minds while we sleep that makes those hours of shut-eye so necessary.

Carol Everson, PhD, is a Professor in the Department of Neurology and in the Department of Cell Biology, Neurobiology and Anatomy at the Medical College of Wisconsin who practices at the Clement J. Zablocki VA Medical Center. The College was recently awarded a four-year, $1.6 million grant from the National Institutes of Health (NIH) to investigate some of the effects of chronic sleep deprivation. In a series of studies, Dr. Everson hopes to answer questions about sleep and its effect on our bodies and health.

Looking for Evidence
"The idea of re-charging is a theme when people try to explain why we need sleep," Dr. Everson says. "It's a sense that people have of what is occurring. We're looking for scientific evidence of exactly what is being restored. Is it the brain? The liver? The skin? What is it, and is it the same for all tissues?"

To find that evidence, Dr. Everson, as a principal investigator for the grant Oxidative Stress Responses to Loss and Recovery of Sleep, is looking at specifically what damage is caused when sleep is withheld. "There are many indications in the population that there are linkages between sleep disorders and other diseases, but we don't know exactly what cells are affected and how those changes would promote disease," Dr. Everson says.

While, for example, scientists have studied the effects of depriving the body of food and know what other problems can be caused by malnutrition, the information about sleep deprivation is limited, says Dr. Everson.

"What we're doing is looking at sleep loss over time. Biochemically, we have some indications that suggest there's what we call uncompensated oxidative damage where cells get injured, but then they're either repaired or eliminated if irreparable." By looking for a greater incidence of cell loss or more cell production to replace damaged cells, Dr. Everson hopes to quantify the specific damages caused by chronic sleep deprivation and where they occur.

In their studies, Dr. Everson and her team have shown that sleep restriction leads to severe metabolic and endocrine disturbances, uncompensated oxidative stress and generalized cell injury. Uncompensated oxidative stress, which leads to cell damage, is a harmful condition caused by an imbalance between oxidative factors and antioxidants.

Not Just for the Brain
"Many people link sleep to the brain. There's a lot of information right now about learning and memory and sleep, but why would we be sleeping for one-third of every 24 hours just to consolidate memory? What are the benefits for the body?" Dr. Everson says. "From my point of view, the control center is in the brain, but just because the control center is there that doesn't mean the function is there. Whatever sleep does for the brain, it probably does for the body, too."

All mammals sleep, Dr. Everson said, and they go through similar stages of sleep. Humans usually pass through five phase of sleep: stages 1, 2, 3, 4 and REM (rapid eye movement) sleep. According to the National Institute of Neurological Disorders and Stroke, we spend almost 50 percent of our total sleep time in stage 2 sleep, about 20 percent in REM sleep and the remaining 30 percent in the other stages.

Sleep Discoveries Might Encourage Changes
When the links between sleep and long-term effects are made, Dr. Everson said we could see changes in health care decision-making. "It would be very similar to what we teach about proper nutrition and exercise," Dr. Everson says. "We would understand how insufficient sleep makes people prone to disease. We would understand what sleep is for, and especially for adolescents, how it affects their development, from bones to ability to perform and so on."

Many critically ill patients get little sleep for a variety of reasons, says Dr. Everson. "If you know sleep is important for survival - as fundamental as eating and drinking water - and you have a person who's very ill and being deprived of a basic need for days, wouldn't you expect it to have an effect on them?" Changes could be made in the way such patients are awakened and interrupted while in the hospital, and intervention on a biochemical level might be possible, she says.

"A lot of people say, 'don't we know this?'" says Dr. Everson. "Many people think we know a lot more than we do about sleep. We know you need it for your health, but we don't know specifically why. We do have critical leads, and breakthrough discoveries seem imminent."

Melissa Rigney Baxter
HealthLink Contributing Writer

MCW Health News presents up-to-date information on patient care and medical research by the physicians of the Medical College of Wisconsin.