At least 40 million Americans each year suffer from chronic, long-term sleep
disorders each year, and an additional 20 million experience occasional sleeping
problems. These disorders and the resulting sleep deprivation interfere with
work, driving, and social activities. They also account for an estimated $16
billion in medical costs each year, while the indirect costs due to lost
productivity and other factors are probably much greater. Doctors have described
more than 70 sleep disorders, most of which can be managed effectively once they
are correctly diagnosed. The most common sleep disorders include insomnia, sleep
apnea, restless legs syndrome, and narcolepsy.
Almost everyone occasionally suffers from short-term insomnia. This problem
can result from stress, jet lag, diet, or many other factors. Insomnia almost
always affects job performance and well-being the next day. About 60 million
Americans a year have insomnia frequently or for extended periods of time, which
leads to even more serious sleep deficits. Insomnia tends to increase with age
and affects about 40 percent of women and 30 percent of men. It is often the
major disabling symptom of an underlying medical disorder.
For short-term insomnia, doctors may prescribe sleeping pills. Most sleeping
pills stop working after several weeks of nightly use, however, and long-term
use can actually interfere with good sleep. Mild insomnia often can be prevented
or cured by practicing good sleep habits. For more serious cases of insomnia,
researchers are experimenting with light therapy and other ways to alter
Sleep apnea is a disorder of interrupted breathing during sleep. It usually
occurs in association with fat buildup or loss of muscle tone with aging. These
changes allow the windpipe to collapse during breathing when muscles relax
during sleep. This problem, called obstructive sleep apnea, is usually
associated with loud snoring (though not everyone who snores has this disorder).
Sleep apnea also can occur if the neurons that control breathing malfunction
During an episode of obstructive apnea, the person’s effort to inhale air
creates suction that collapses the windpipe. This blocks the air flow for 10
seconds to a minute while the sleeping person struggles to breathe. When the
person’s blood oxygen level falls, the brain responds by awakening the person
enough to tighten the upper airway muscles and open the windpipe. The person may
snort or gasp, then resume snoring. This cycle may be repeated hundreds of times
a night. The frequent awakenings that sleep apnea patients experience leave them
continually sleepy and may lead to personality changes such as irritability or
depression. Sleep apnea also deprives the person of oxygen, which can lead to
morning headaches, a loss of interest in sex, or a decline in mental
functioning. It also is linked to high blood pressure, irregular heartbeats, and
an increased risk of heart attacks and stroke. Patients with severe, untreated
sleep apnea are two to three times more likely to have automobile accidents than
the general population. In some high-risk individuals, sleep apnea may even lead
to sudden death from respiratory arrest during sleep.
An estimated 18 million Americans have sleep apnea. However, few of them have
had the problem diagnosed. Patients with the typical features of sleep apnea,
such as loud snoring, obesity, and excessive daytime sleepiness, should be
referred to a specialized sleep center that can perform a test called
polysomnography. This test records the patient’s brain waves, heartbeat, and
breathing during an entire night. If sleep apnea is diagnosed, several
treatments are available. Mild sleep apnea frequently can be overcome through
weight loss or by preventing the person from sleeping on his or her back. Other
people may need special devices or surgery to correct the obstruction. People
with sleep apnea should never take sedatives or sleeping pills, which can
prevent them from awakening enough to breathe.
Restless Legs Syndrome
Restless legs syndrome (RLS), a familial disorder causing unpleasant
crawling, prickling, or tingling sensations in the legs and feet and an urge to
move them for relief, is emerging as one of the most common sleep disorders,
especially among older people. This disorder, which affects as many as 12
million Americans, leads to constant leg movement during the day and insomnia at
night. Severe RLS is most common in elderly people, though symptoms may develop
at any age. In some cases, it may be linked to other conditions such as anemia,
pregnancy, or diabetes.
Many RLS patients also have a disorder known as periodic limb movement
disorder or PLMD, which causes repetitive jerking movements of the
limbs, especially the legs. These movements occur every 20 to 40 seconds and
cause repeated awakening and severely fragmented sleep. In one study, RLS and
PLMD accounted for a third of the insomnia seen in patients older than age 60.
RLS and PLMD often can be relieved by drugs that affect the neurotransmitter
dopamine, suggesting that dopamine abnormalities underlie these disorders’
symptoms. Learning how these disorders occur may lead to better therapies in the
Narcolepsy affects an estimated 250,000 Americans. People with narcolepsy
have frequent “sleep attacks” at various times of the day, even if they have had
a normal amount of night-time sleep. These attacks last from several seconds to
more than 30 minutes. People with narcolepsy also may experience cataplexy (loss
of muscle control during emotional situations), hallucinations, temporary
paralysis when they awaken, and disrupted night-time sleep. These symptoms seem
to be features of REM sleep that appear during waking, which suggests that
narcolepsy is a disorder of sleep regulation. The symptoms of narcolepsy
typically appear during adolescence, though it often takes years to obtain a
correct diagnosis. The disorder (or at least a predisposition to it) is usually
hereditary, but it occasionally is linked to brain damage from a head injury or
Once narcolepsy is diagnosed, stimulants, antidepressants, or other drugs can
help control the symptoms and prevent the embarrassing and dangerous effects of
falling asleep at improper times. Naps at certain times of the day also may
reduce the excessive daytime sleepiness.
In 1999, a research team working with canine models identified a gene that
causes narcolepsy – breakthrough that brings a cure for this disabling condition
within reach. The gene, hypocretin receptor 2, codes for a protein that allows
brain cells to receive instructions from other cells. The defective versions of
the gene encode proteins that cannot recognize these messages, perhaps cutting
the cells off from messages that promote wakefulness. The researchers know that
the same gene exists in humans, and they are currently searching for defective
versions in people with narcolepsy.
Sleep: A Dynamic Activity
Until the 1950s, most people thought of sleep as a passive, dormant part of
our daily lives. We now know that our brains are very active during sleep.
Moreover, sleep affects our daily functioning and our physical and mental health
in many ways that we are just beginning to understand.
Nerve-signaling chemicals called neurotransmitters control whether we
are asleep or awake by acting on different groups of nerve cells, or neurons, in
the brain. Neurons in the brainstem, which connects the brain with the spinal
cord, produce neurotransmitters such as serotonin and norepinephrine that keep
some parts of the brain active while we are awake. Other neurons at the base of
the brain begin signaling when we fall asleep. These neurons appear to “switch
off” the signals that keep us awake. Research also suggests that a chemical
called adenosine builds up in our blood while we are awake and causes
drowsiness. This chemical gradually breaks down while we sleep.
During sleep, we usually pass through five phases of sleep: 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 with stage 1. 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. Infants, by
contrast, spend about half of their sleep time in REM sleep.
During stage 1, which is light sleep, we drift in and out of sleep and can be
awakened easily. Our eyes move very slowly and muscle activity slows. People
awakened from stage 1 sleep often remember fragmented visual images. Many also
experience sudden muscle contractions called hypnic myoclonia, often
preceded by a sensation of starting to fall. These sudden movements are similar
to the “jump” we make when startled. When we enter stage 2 sleep, our eye
movements stop and our brain waves (fluctuations of electrical activity that can
be measured by electrodes) become slower, with occasional bursts of rapid waves
called sleep spindles. In stage 3, extremely slow brain waves called
delta waves begin to appear, interspersed with smaller, faster waves. By
stage 4, the brain produces delta waves almost exclusively. It is very difficult
to wake someone during stages 3 and 4, which 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.
When we switch into 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 tales – dreams.
The first REM sleep period usually occurs about 70 to 90 minutes after we
fall asleep. 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. By morning, people spend nearly all their
sleep time in stages 1, 2, and REM.
People awakened after sleeping more than a few minutes are usually unable to
recall the last few minutes before they fell asleep. This sleep-related form of
amnesia is the reason people often forget telephone calls or conversations
they’ve had in the middle of the night. It also explains why we often do not
remember our alarms ringing in the morning if we go right back to sleep after
turning them off.
Since sleep and wakefulness are influenced by different neurotransmitter
signals in the brain, foods and medicines that change the balance of these
signals affect whether we feel alert or drowsy and how well we sleep.
Caffeinated drinks such as coffee and drugs such as diet pills and decongestants
stimulate some parts of the brain and can cause insomnia, or an inability
to sleep. 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. Many people who suffer
from insomnia try to solve the problem with alcohol – the so-called night cap.
While alcohol does help people fall into light sleep, 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, so abnormally hot or cold temperatures in the environment can disrupt this
stage of sleep. If our REM sleep is disrupted one night, our bodies don’t follow
the normal sleep cycle progression the next time we doze off. Instead, we often
slip directly into REM sleep and go through extended periods of REM until we
“catch up” on this stage of sleep.
People who are under anesthesia or in a coma are often said to be asleep.
However, people in these conditions cannot be awakened and do not produce the
complex, active brain wave patterns seen in normal sleep. Instead, their brain
waves are very slow and weak, sometimes all but undetectable.