What Is Sleep?
Sleep was long considered just a block of time when your brain and body shut down. Thanks to sleep research studies done over the past several decades, it is now known that sleep has distinct stages that cycle throughout the night in predictable patterns. How well rested you are and how well you function depend not just on your total sleep time but on how much sleep you get each night and the timing of your sleep stages. Your brain and body functions stay active throughout sleep, and each stage of sleep is linked to a specific type of brain waves (distinctive patterns of electrical activity in the brain). Sleep is divided into two basic types: rapid eye movement (REM) sleep and non-REM sleep (with three different stages). Typically, sleep begins with non-REM sleep. In stage 1 non-REM sleep, you sleep lightly and can be awakened easily by noises or other disturbances. During this first stage of sleep, your eyes move slowly, your muscles relax, and your heart and breathing rates begin to slow. You then enter stage 2 non-REM sleep, which is defined by slower brain waves with occasional bursts of rapid waves. You spend about half the night in this stage. When you progress into stage 3 non- REM sleep, your brain waves become even slower, and the brain produces extremely slow waves almost exclusively (called Delta waves). Stage 3 is a very deep stage of sleep, during which it is very difficult to be awakened. Children who wet the bed or sleep walk tend to do so during stage 3 of non-REM sleep. Deep sleep is considered the “restorative” stage of sleep that is necessary for feeling well-rested and energetic during the day. During REM sleep, your eyes move rapidly in different directions, even though your eyelids stay closed. Your breathing also becomes more rapid, irregular, and shallow, and your heart rate and blood pressure increase. Dreaming typically occurs during REM sleep. During this type of sleep, your arm and leg muscles are temporarily paralyzed so that you cannot “act out” any dreams that you may be having.
You typically first enter REM sleep about an hour to an hour and a half after falling asleep. After that, the sleep stages repeat themselves continuously while you sleep. As you sleep, REM sleep time becomes longer, while time spent in stage 3 non-REM sleep becomes shorter. By the time you wake up, nearly all your sleep time has been spent in stages 1 and 2 of non-REM sleep and in REM sleep. If REM sleep is severely disrupted during one night, REM sleep time is typically longer than normal in subsequent nights until you catch up. Overall, almost one-half of your total sleep time is spent in stage 2 non-REM sleep and about one-fifth each in deep sleep (stage 3 of non-REM sleep) and REM sleep. In contrast, infants spend half or more of their total sleep time in REM sleep. Gradually, as they grow, the percentage of total sleep time they spend in REM continues to decrease, until it reaches the one-fifth level typical of later childhood and adulthood.
Why people dream and why REM sleep is so important are not well understood. It is known that REM sleep stimulates the brain regions you use to learn and make memories. Animal studies suggest that dreams may reflect the brain’s sorting and selectively storing new information acquired during wake time. While this information is processed, the brain might revisit scenes from the day and mix them randomly. Dreams are generally recalled when we wake briefly or are awakened by an alarm clock or some other noise in the environment. Studies show, however, that other stages of sleep besides REM also are needed to form the pathways in the brain that enable us to learn and remember.
What Makes You Sleep?
Although you may put off going to sleep in order to squeeze more activities into your day, eventually your need for sleep becomes overwhelming. This need appears to be due, in part, to two substances your body produces. One substance, called adenosine, builds up in your blood while you’re awake. Then, while you sleep, your body breaks down the adenosine. Levels of this substance in your body may help trigger sleep when needed. A buildup of adenosine and many other complex factors might explain why, after several nights of less than optimal amounts of sleep, you build up a sleep debt. This may cause you to sleep longer than normal or at unplanned times during the day. Because of your body’s internal processes, you can’t adapt to getting less sleep than your body needs. Eventually, a lack of sleep catches up with you.
The other substance that helps make you sleep is a hormone called melatonin. This hormone makes you naturally feel sleepy at night. It is part of your internal “biological clock,” which controls when you feel sleepy and your sleep patterns. Your biological clock is a small bundle of cells in your brain that works throughout the day and night. Internal and external environmental cues, such as light signals received through your eyes, control these cells. Your biological clock triggers your body to produce melatonin, which helps prepare your brain and body for sleep. As melatonin is released, you’ll feel increasingly drowsy. Because of your biological clock, you naturally feel the most tired between midnight and 7 a.m. You also may feel mildly sleepy in the afternoon between 1 p.m. and 4 p.m. when another increase in melatonin occurs in your body.
Your biological clock makes you the most alert during daylight hours and the least alert during the early morning hours. Consequently, most people do their best work during the day. Our 24/7 society, however, demands that some people work at night. Nearly one-quarter of all workers work shifts that are not during the daytime, and more than two-thirds of these workers have problem sleepiness and/or difficulty sleeping. Because their work schedules are at odds with powerful sleep-regulating cues like sunlight, night shift workers often find themselves drowsy at work, and they have difficulty falling or staying asleep during the daylight hours when their work schedules require them to sleep. The fatigue experienced by night shift workers can be dangerous. Night shift workers also are at greater risk of being in car crashes when they drive home from work during the early morning hours, because the biological clock is not sending out an alerting signal. One study found that one-fifth of night shift workers had a car crash or a near miss in the preceding year because of sleepiness on the drive home from work. Night shift workers are also more likely to have physical problems, such as heart disease, digestive troubles, and infertility, as well as emotional problems. All of these problems may be related, at least in part, to the workers’ chronic sleepiness, possibly because their biological clocks are not in tune with their work schedules.
What Disrupts Sleep?
Many factors can prevent a good night’s sleep. These factors range from well-known stimulants, such as coffee, to certain pain relievers, decongestants, and other culprits. Many people depend on the caffeine in coffee, cola, or tea to wake them up in the morning or to keep them awake. Caffeine is thought to block the cell receptors that adenosine (a substance in the brain) uses to trigger its sleep-inducing signals. In this way, caffeine fools the body into thinking it isn’t tired. It can take as long as 6–8 hours for the effects of caffeine to wear off completely. Thus, drinking a cup of coffee in the late afternoon may prevent your falling asleep at night.
Nicotine is another stimulant that can keep you awake. Nicotine also leads to lighter than normal sleep, and heavy smokers tend to wake up too early because of nicotine withdrawal. Although alcohol is a sedative that makes it easier to fall asleep, it prevents deep sleep and REM sleep, allowing only the lighter stages of sleep. People who drink alcohol also tend to wake up in the middle of the night when the effects of an alcoholic “nightcap” wear off.
Certain commonly used prescription and over-the-counter medicines contain ingredients that can keep you awake. These ingredients include decongestants and steroids. Many medicines taken to relieve headaches contain caffeine. Heart and blood pressure medications known as beta blockers can make it difficult to fall asleep and cause more awakenings during the night. People who have chronic asthma or bronchitis also have more problems falling asleep and staying asleep than healthy people, either because of their breathing difficulties or because of the medicines they take. Other chronic painful or uncomfortable conditions— such as arthritis, congestive heart failure, and sickle cell anemia— can disrupt sleep, too.
A number of psychological disorders—including schizophrenia, bipolar disorder, and anxiety disorders—are well known for disrupting sleep. Depression often leads to insomnia, and insomnia can cause depression. Some of these psychological disorders are more likely to disrupt REM sleep. Psychological stress also takes its toll on sleep, making it more difficult to fall asleep or stay asleep. People who feel stressed also tend to spend less time in deep sleep and REM sleep. Many people report having difficulties sleeping if, for example, they have recently lost a loved one, are going through a divorce, or are under stress at work.
Menstrual cycle hormones can affect how well women sleep. Progesterone is known to induce sleep and circulates in greater concentrations in the second half of the menstrual cycle. For this reason, women may sleep better during this phase of their menstrual cycle. On the other hand, many women report trouble sleeping the night before their menstrual flow starts. This sleep disruption may be related to the abrupt drop in progesterone levels that occurs just before menstruation. Women in their late forties and early fifties, however, report more difficulties sleeping (insomnia) than younger women. These difficulties may be linked to menopause, when they have lower concentrations of progesterone. Hot flashes in women of this age also may cause sleep disruption and difficulties.
Certain lifestyle factors also may deprive a person of needed sleep. Large meals or vigorous exercise just before bedtime can make it harder to fall asleep. While vigorous exercise in the evening may delay sleep onset for various reasons, exercise in the daytime is associated with improved nighttime sleep. If you aren’t getting enough sleep or aren’t falling asleep early enough, you may be overscheduling activities that can prevent you from getting the quiet relaxation time you need to prepare for sleep. Most people report that it’s easier to fall asleep if they have time to wind down into a less active state before sleeping. Relaxing in a hot bath or having a hot, caffeine-free beverage before bedtime may help. In addition, your body temperature drops after a hot bath in a way that mimics, in part, what happens as you fall asleep. Probably for both these reasons, many people report that they fall asleep more easily after a hot bath.
Your sleeping environment also can affect your sleep. Clear your bedroom of any potential sleep distractions, such as noises, bright lights, a TV, a cell phone, or computer. Having a comfortable mattress and pillow can help promote a good night’s sleep. You also sleep better if the temperature in your bedroom is kept on the cool side. For more ideas on improving your sleep, check out the tips for getting a good night’s sleep.
Information from the National Institutes of Health
Tips for Getting a Good Night’s Sleep
Stick to a sleep schedule. Go to bed and wake up at the same time each day. As creatures of habit, people have a hard time adjusting to changes in sleep patterns. Sleeping later on weekends won’t fully make up for a lack of sleep during the week and will make it harder to wake up early on Monday morning.
Exercise is great, but not too late in the day. Try to exercise at least 30 minutes on most days but not later than 2–3 hours before your bedtime.
Avoid caffeine and nicotine. Coffee, colas, certain teas, and chocolate contain the stimulant caffeine, and its effects can take as long as 8 hours to wear off fully. Therefore, a cup of coffee in the late afternoon can make it hard for you to fall asleep at night. Nicotine is also a stimulant, often causing smokers to sleep only very lightly. In addition, smokers often wake up too early in the morning because of nicotine withdrawal.
Avoid alcoholic drinks before bed. Having a “nightcap” or alcoholic beverage before sleep may help you relax, but heavy use robs you of deep sleep and REM sleep, keeping you in the lighter stages of sleep. Heavy alcohol ingestion also may contribute to impairment in breathing at night. You also tend to wake up in the middle of the night when the effects of the alcohol have worn off.
Avoid large meals and beverages late at night. A light snack is okay, but a large meal can cause indigestion that interferes with sleep. Drinking too many fluids at night can cause frequent awakenings to urinate.
If possible, avoid medicines that delay or disrupt your sleep. Some commonly prescribed heart, blood pressure, or asthma medications, as well as some over-the-counter and herbal remedies for coughs, colds, or allergies, can disrupt sleep patterns. If you have trouble sleeping, talk to your doctor or pharmacist to see whether any drugs you’re taking might be contributing to your insomnia, and ask whether they can be taken at other times during the day or early in the evening.
Don’t take naps after 3 p.m. Naps can help make up for lost sleep, but late afternoon naps can make it harder to fall asleep at night.
Relax before bed. Don’t overschedule your day so that no time is left for unwinding. A relaxing activity, such as reading or listening to music, should be part of your bedtime ritual.
Take a hot bath before bed. The drop in body temperature after getting out of the bath may help you feel sleepy, and the bath can help you relax and slow down so you’re more ready to sleep.
Have a good sleeping environment. Get rid of anything in your bedroom that might distract you from sleep, such as noises, bright lights, an uncomfortable bed, or warm temperatures. You sleep better if the temperature in the room is kept on the cool side. A TV, cell phone, or computer in the bedroom can be a distraction and deprive you of needed sleep. Having a comfortable mattress and pillow can help promote a good night’s sleep. Individuals who have insomnia often watch the clock. Turn the clock’s face out of view so you don’t worry about the time while trying to fall asleep.
Have the right sunlight exposure. Daylight is key to regulating daily sleep patterns. Try to get outside in natural sunlight for at least 30 minutes each day. If possible, wake up with the sun or use very bright lights in the morning. Sleep experts recommend that, if you have problems falling asleep, you should get an hour of exposure to morning sunlight and turn down the lights before bedtime.
Don’t lie in bed awake. If you find yourself still awake after staying in bed for more than 20 minutes or if you are starting to feel anxious or worried, get up and do some relaxing activity until you feel sleepy. The anxiety of not being able to sleep can make it harder to fall asleep.
See a doctor if you continue to have trouble sleeping. If you consistently find it difficult to fall or stay asleep and/ or feel tired or not well-rested during the day despite spending enough time in bed at night, you may have a sleep disorder. Your family doctor or a sleep specialist should be able to help you, and it is important to rule out other health or psychiatric problems that may be disturbing your sleep.
