A number of tasks vital to health and quality of life are linked to sleep, and these tasks are impaired when you are sleep deprived.
Learning, Memory, and Mood
Students who have trouble grasping new information or learning new skills are often advised to “sleep on it,” and that advice seems well founded. Recent studies reveal that people can learn a task better if they are well rested. They also can remember better what they learned if they get a good night’s sleep after learning the task than if they are sleep deprived. Volunteers had to sleep at least 6 hours to show improvement in learning, and the amount of improvement was directly tied to how much time they slept. In other words, volunteers who slept 8 hours outperformed those who slept only 6 or 7 hours. Other studies suggest that all the benefits of training for mentally challenging tasks are maximized after a good night’s sleep, rather than immediately following the training or after sleeping for a short period overnight. Many well-known artists and scientists claim to have had creative insights while they slept.
Mary Shelley, for example, said the idea for her novel Frankenstein came to her in a dream. Although it has not been shown that dreaming is the driving force behind innovation, one study suggests that sleep is needed for creative problem solving. In that study, volunteers were asked to perform a memory task and then were tested 8 hours later. Those who were allowed to sleep for 8 hours immediately after receiving the task and before being tested were much more likely to find a creative way of simplifying the task and improving their performance compared to those who were awake the entire 8 hours before being tested.
Exactly what happens during sleep to improve our learning, memory, and insight isn’t known. Experts suspect, however, that while people sleep, they form or reinforce the pathways of brain cells needed to perform these tasks. This process may explain why sleep is needed for proper brain development in infants.
Not only is a good night’s sleep required to form new learning and memory pathways in the brain, but sleep is also necessary for those pathways to work up to speed. Several studies show that lack of sleep causes thinking processes to slow down. Lack of sleep also makes it harder to focus and pay attention. Lack of sleep can make you more easily confused. Studies also find a lack of sleep leads to faulty decisionmaking and more risk taking. A lack of sleep slows down your reaction time, which is particularly significant to driving and other tasks that require quick response. When people who lack sleep are tested by using a driving simulator, they perform just as poorly as people who are drunk. (See “Crash in Bed Not on the Road”.) The bottom line is: not getting a good night’s sleep can be dangerous!
Even if you don’t have a mentally or physically challenging day ahead of you, you should still get enough sleep to put yourself in a good mood. Most people report being irritable, if not downright unhappy, when they lack sleep. People who chronically suffer from a lack of sleep, either because they do not spend enough time in bed or because they have an untreated sleep disorder, are at greater risk of developing depression. One group of people who usually don’t get enough sleep is mothers of newborns. Some experts think depression after childbirth (postpartum blues) is caused, in part, by a lack of sleep.
Sleep gives your heart and vascular system a much-needed rest.
During non-REM sleep, your heart rate and blood pressure progressively slow as you enter deeper sleep. During REM sleep, your heart rate and blood pressure have boosted spikes of activity. Overall, however, sleep reduces your heart rate and blood pressure by about 10 percent.
If you don’t get enough sleep, this nightly dip in blood pressure, which appears to be important for good cardiovascular health, may not occur. According to several studies, if your blood pressure does not dip during sleep, you are more likely to experience strokes, chest pain known as angina, an irregular heartbeat, and heart attacks. You are also more likely to develop congestive heart failure, a condition in which fluid builds up in the body because the heart is not pumping sufficiently. Failure to experience the normal dip in blood pressure during sleep can be related to insufficient sleep time, an untreated sleep disorder, or other factors. African Americans, for example, tend not to have as much of a dip in blood pressure during sleep. This difference may help to explain why they are more likely than Caucasians to have serious cardiovascular disease.
A lack of sleep also puts your body under stress and may trigger the release of more adrenaline, cortisol, and other stress hormones during the day. These hormones contribute to your blood pressure not dipping during sleep, thereby increasing the risk for heart disease. Inadequate sleep may also negatively affect your heart and vascular system by the increased production of certain proteins thought to play a role in heart disease. For example, some studies find that people who chronically do not get enough sleep have higher blood levels of C-reactive protein. Higher levels of this protein may suggest a greater risk of developing hardening of the arteries (atherosclerosis).
When you were young, your mother may have told you that you need to get enough sleep to grow strong and tall. She may have been right! Deep sleep triggers more release of growth hormone, which fuels growth in children and boosts muscle mass and the repair of cells and tissues in children and adults. Sleep’s effect on the release of sex hormones also encourages puberty and fertility.
Consequently, women who work at night and tend to lack sleep are, therefore, more likely to have trouble conceiving or to miscarry.
Your mother also probably was right if she told you that getting a good night’s sleep on a regular basis would help keep you from getting sick and help you get better if you do get sick. During sleep, your body creates more cytokines - cellular hormones that help the immune system fight various infections. Lack of sleep can reduce the ability to fight off common infections. Research also reveals that a lack of sleep can reduce the body’s response to the flu vaccine.
For example, sleep-deprived volunteers given the flu vaccine produced less than half as many flu antibodies as those who were well rested and given the same vaccine.
Although lack of exercise and other factors are important contributors, the current epidemic of diabetes and obesity appears to be related, at least in part, to chronically getting inadequate sleep.
Evidence is growing that sleep is a powerful regulator of appetite, energy use, and weight control. During sleep, the body’s production of the appetite suppressor leptin increases, and the appetite stimulant grehlin decreases. Studies find that the less people sleep, the more likely they are to be overweight or obese and prefer eating foods that are higher in calories and carbohydrates. People who report an average total sleep time of 5 hours a night, for example, are much more likely to become obese compared to people who sleep 7 - 8 hours a night.
A number of hormones released during sleep also control the body’s use of energy. A distinct rise and fall of blood sugar levels during sleep appears to be linked to sleep stage. Not getting enough sleep overall or enough of each stage of sleep disrupts this pattern. One study found that, when healthy young men slept only 4 hours a night for 6 nights in a row, their insulin and blood sugar levels mimicked those seen in people who were developing diabetes. Another study found that women who slept less than 7 hours a night were more likely to develop diabetes over time than those who slept between 7 and 8 hours a night.
Revision date: July 5, 2011
Last revised: by Tatiana Kuznetsova, D.M.D.