Although scientists are still trying to learn exactly why people need sleep, animal studies show that sleep is necessary for survival. For example, while rats normally live for two to three years, those deprived of REM sleep survive only about 5 weeks on average, and rats deprived of all sleep stages live only about 3 weeks. Sleep-deprived rats also develop abnormally low body temperatures and sores on their tail and paws. The sores may develop because the rats' immune systems become impaired. Some studies suggest that sleep deprivation affects the immune system in detrimental ways.
Sleep appears necessary for our nervous systems to work properly. Too little sleep leaves us drowsy and unable to concentrate the next day. It also leads to impaired memory and physical performance and reduced ability to carry out math calculations. If sleep deprivation continues, hallucinations and mood swings may develop. Some experts believe sleep gives neurons used while we are awake a chance to shut down and repair themselves. Without sleep, neurons may become so depleted in energy or so polluted with byproducts of normal cellular activities that they begin to malfunction. Sleep also may give the brain a chance to exercise important neuronal connections that might otherwise deteriorate from lack of activity.
Deep sleep coincides with the release of growth hormone in children and young adults. Many of the body's cells also show increased production and reduced breakdown of proteins during deep sleep. Since proteins are the building blocks needed for cell growth and for repair of damage from factors like stress and ultraviolet rays, deep sleep may truly be "beauty sleep." Activity in parts of the brain that control emotions, decision-making processes, and social interactions is drastically reduced during deep sleep, suggesting that this type of sleep may help people maintain optimal emotional and social functioning while they are awake. A study in rats also showed that certain nerve-signaling patterns that the rats generated during the day were repeated during deep sleep. This pattern repetition may help encode memories and improve learning.
Neurons that control sleep interact closely with the immune system. The chemicals our immune systems produce while fighting an infection are powerful sleep-inducing chemicals. Sleep may help the body conserve energy and other resources that the immune system needs to mount an attack. Sleep deprivation weakens the immune system leaving us more susceptible to other diseases and disorders like diabetes, cancer and even the common cold. It also alters the way your brain functions and impedes brain activity. In fact, sleep is as necessary to maintaining health and life as food and water and almost as important as the air we breathe.
How Much Sleep Do We Need?
Infants: about 16 hours a day
Teenagers: about 9 hours a night
Adults: 7 to 8 hours a night, but women in the first 3 months of pregnancy often need several more hours of sleep than usual.
Sleep Debt
Getting too little sleep creates a "sleep debt," which is much like being overdrawn at a bank. Eventually, your body will demand that the debt be repaid. We don't seem to adapt to getting less sleep than we need, while we may get used to a sleep-depriving schedule, our judgment, reaction time, and other functions are still impaired. The widespread practice of "burning the candle at both ends" in western industrialized societies has created so much sleep deprivation that what is really abnormal sleepiness is now almost the norm.
Sleep Deprivation Is Dangerous
Sleep-deprived people perform as badly as or worse than those who are intoxicated, and driver fatigue accounts for an estimated 100,000 motor vehicle accidents and 1500 deaths each year, according to the National Highway Traffic Safety Administration. Since drowsiness is the brain's last step before falling asleep, driving while drowsy can lead to disaster.
Sleep Affects Our Mental and Physical Health
Our sleep cycle consists of stages 1, 2, 3, 4, and REM (rapid eye movement) sleep. These stages progress in a cycle from stage 1 to REM sleep, then the cycle starts over again.
Stage 1: We drift in and out of sleep and can be awakened easily. Our eyes move very slowly and muscle activity slows.
Stage 2: Our eye movements stop and our brain waves become slower.
Stage 3: Extremely slow brain waves called delta waves begin to appear, interspersed with smaller, faster waves.
Stage 4: The brain produces delta waves almost exclusively. It is very difficult to wake someone during stages 3 and 4, and these stages together are called deep sleep. There is no eye movement or muscle activity. People awakened during deep sleep do not adjust immediately and often feel groggy and disoriented for several minutes after they wake up. Some children experience bedwetting, night terrors, or sleepwalking during deep sleep.
REM sleep: Our breathing becomes more rapid, irregular, and shallow, our eyes jerk rapidly in various directions, and our limb muscles become temporarily paralyzed. Our heart rate increases, our blood pressure rises, and males develop penile erections. When people awaken during REM sleep, they often describe bizarre and illogical talesdreams.
A complete sleep cycle takes 90 to 110 minutes on average. The first sleep cycles each night contain relatively short REM periods and long periods of deep sleep. As the night progresses, REM sleep periods increase in length while deep sleep decreases.
The Effect of Foods and Medicines On Sleep
Caffeinated drinks such as coffee and drugs such as diet pills and decongestants stimulate some parts of the brain and can cause insomnia. Many antidepressants suppress REM sleep. Heavy smokers often sleep very lightly and have reduced amounts of REM sleep. They also tend to wake up after 3 or 4 hours of sleep due to nicotine withdrawal. Alcohol does help people fall into light sleep, but it also robs them of REM and the deeper, more restorative stages of sleep. Instead, it keeps them in the lighter stages of sleep, from which they can be awakened easily.
People lose some of the ability to regulate their body temperature during REM, and abnormally hot or cold temperatures in the environment can disrupt this stage of sleep.
