Circadian Rhythms
Circadian rhythms influence body temperature, sleep and wakefulness and a
variety of hormonal changes. Sunlight and other time cues help to set and
maintain circadian cycles. Even without these time cues from the great outdoors,
fluctuations in circadian rhythms would continue to occur within a period of about
one day. Circadian rhythms are coordinated by small nuclei at the base of the
brain, the suprachiasmatic nuclei (SCN). The SCN have connections with other
parts of the brain to control the body's temperature, hormone release and other
functions. A pathway runs from the eye to the SCN and light seems to play the
largest role in setting the circadian "clock". Blind people often report problems
with circadian rhythms, since it is difficult for them to get the time cues needed to
set their circadian rhythm. Other factors that may affect the SCN and the setting
of the circadian clock include changes in body temperature and medications.
Body temperature, for example, starts to rise during the later hours of sleep, just
before waking up. This seems to promote a feeling of alertness upon awakening
in the morning. In the evening, body temperatures decrease in preparation for
sleep. A drop in temperature also occurs in most people between 12 and 4pm,
which may explain why many people feels sleepy in the early afternoon. Although
it has yet to be proven that changes in body temperature determine our sleep
habits, there does appear to be a relationship between the two.
Jet lag
The most commonly experienced problem with circadian rhythm is jet lag. Jet
lag occurs when a person travels across several time zones within a day or two.
A typical flight across seas, often produces jet lag symptoms that can last for a
week or more. These symptoms include daytime sleepiness, insomnia,
indigestion, irritability and poor concentration. Some people adapt more quickly
than others, depending on the number of the time zones involved. Another
example of a jet lag scenario is a shift worker. When changing back and forth to
different sleep/ wake patterns, often a person experiences the same symptoms.
Tips for coping with jet lag and shift work
1. Allow extra time for adjustment during a trip or when switching to a new
work schedule.
2. Depending upon the new time zone, a 20 to 30 minute nap at a specific
time of day can be useful in overcoming the jet lag symptoms.
3. The occasional use of short-acting sleeping medications can help reduce
the symptoms of the circadian rhythm disorder. Check with a healthcare provider
before taking any medications and never mix sleeping pills with alcohol or a
antihistamines. Keep in mind these are for temporary use only and the
effectiveness may fade within a month's time.
