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Sleep that routinely occurs at odd times of the day may be caused
by a disorder of the timing system for sleep. People with a
malfunction of the biological clock for sleep may be literally
unable to fall asleep until the wee hours of the morning and
then need to sleep until the next afternoon in order to get enough
sleep. Less commonly, others may be unable to stay awake past
the late afternoon and then wake in the middle of the night,
having had plenty of sleep while wondering why they feel no choice
but to get up when the world is still dark.
A number of routine activities reflect the presence of this
timing system. We tend to sleep at night and be up in the daytime
(nocturnal animals reverse this pattern). We tend to have the
urge to eat at certain times and to be better at exercise and
high level mental activity at certain times of the day and less
so at other times. This is due in part to a number of hormones
and neurotransmitters or chemical messengers that fluctuate in
their levels of activity on a nearly, but not exactly, 24-hour
basis. It is the approximate nature of this timing system that
lends itself to “disorders” in cases in which the system is unable
to fit within the confines of a 24-hour day.
The onset of sleep occurs as hormones and chemical messengers
that help to induce sleep are produced in greater quantity and
become more active in the evening, rising to peak levels in the
late evening and supporting the entry into sleep. At the same
time, levels of chemical messengers that cause us to be awake
and alert are subsiding, such that the difference between the
two is quite distinct as we go to sleep. In the morning, this
process must reverse itself so that the alerting chemistry is
dominant and the sleep-inducing chemistry has shut off. With
normal sleep, exposure to bright daylight in the morning re-sets
and subtly adjusts the circadian rhythm as needed in order to
maintain a 24-hour schedule for sleep.
Below is a schematic illustrating normal biochemical
fluctuation in the circadian rhythm for sleep.
Circadian rhythm disorders of sleep arise when the system described
above goes awry.
Shift Work Sleep Disorder
In our round-the-clock work society, this is undoubtedly the
most common circadian rhythm disorder. It manifests when a night
or rotating shift worker has difficulty getting enough sleep
during the day time. It probably does not reflect a genetically-determined
disorder of the circadian timing system, but rather a breakdown
in the system that is trying to cope with an abnormal schedule
for sleep. Treatment can help minimize this impact.
Delayed Sleep Phase Syndrome
This is probably the most common disorder of the circadian timing
for sleep. The disorder usually begins in the early teens and
can persist throughout adulthood. People with this disorder
complain of the symptom of insomnia at the beginning
of the night, and in extreme cases are unable to go to sleep
until near sunrise. They then sleep through the morning and
often into the mid-afternoon hours, resulting in the symptom
of excessive daytime sleepiness in the early part of the
day. They go on to feel fully alert later in the evening and
during night time hours when other people are asleep.
Advanced Sleep Phase Syndrome
This is essentially
the reverse of a delayed sleep phase. People with this disorder
find themselves unable to stay awake past late afternoon or early
evening and then have a normal duration of sleep, resulting in
waking for their day often as early as 2:00 am.
Treatment
Circadian rhythm disorders can obviously cause serious difficulties
in maintaining a normal work or school schedule. Standard sleep
medications, while they may cause some drowsiness, do not typically
have major effects on the timing of sleep. The successful
mainstay treatments for circadian rhythm disorders have been
behavioral in nature. Scheduling regimes emphasizing timed
exposure to bright light have been the most effective
behavioral treatments for moving an unruly sleep schedule into
a more desirable time frame. These need to be coached and
supervised by a sleep specialist knowledgeable in the treatment
of circadian rhythm disorders. Very recently, one prescription
medication has become available that may have positive effects
on the circadian rhythm system. Over-the-counter melatonin has
also been used with some success but understanding how to select
the time to take it is critical to its effectiveness and its
use for this purpose should be guided by a knowledgeable sleep
specialist. Poorly timed treatments of any type can, in some
cases, make matters worse. Additional medications that may ultimately
prove helpful are still under development. |
