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Do you live
by the clock, checking your watch so you're not late for work, school
or appointments? While you struggle to stay on time for your daily activities,
your body has its own internal clock. This biological clock helps you
feel alert at work, hungry at mealtime and drowsy at night. When your
internal clock is out of whack, your health can suffer. Scientists have
long known that the human body has daily rhythms, called circadian rhythms
(circadian is Latin for "around a day"). These natural rhythms are coordinated
by a tiny region in your brain. This "master clock" generally operates
on a 24-hour cycle, and it adjusts to several cues in your surroundings.
The most important cue is light and darkness. During the day, when it's
light outside, the brain's master clock sends out signals to other brain
regions to make hormones that will help keep you awake, boost your heart
rate and give you energy. In the evening, when less light enters your
eyes, the master clock triggers production of a hormone called melatonin.
Melatonin makes you feel drowsy and helps you stay asleep. The brain's
clock affects various body functions, including body temperature, hormone
levels, urine production and blood pressure. "Many processes are patterned
around a 24-hour cycle: sleeping, eating, waking, drinking and even
health-related events," says Dr. Martha Gillette, a scientist at the
University of Illinois at Urbana-Champaign. For instance, she notes,
heart attacks are more likely to occur early in the morning, when the
level of a hormone called cortisol starts its daily rise. Time of day
has also been shown to influence the effectiveness and side-effects
of certain drugs. When you fight against your circadian clock and your
activities take you out of sync with day and night, your health may
suffer. The schedules of shift workers who must be on the job after
the sun goes down are at odds with their biological clocks. These people
often find themselves sleepy at work. They may also have trouble falling
or staying asleep during daylight hours after work. Studies show that
shift workers have increased risk for heart disease, digestive disturbances,
cancer and other health problems. Another less severe disruption of
the circadian clock is jet lag. It's caused by traveling across time
zones. Jet lag is usually more severe for eastbound travelers, because
their days are shortened and the brain has more trouble adjusting to
a shorter day than a longer one. Some studies suggest that taking melatonin
pills just before bedtime may help jet-lagged travelers adjust to new
time zones. But the scientific evidence for using melatonin to treat
sleep disorders is still unclear. In recent years, researchers have
discovered that circadian activities are far more complicated than they'd
ever expected. Inside our cells, clock genes and proteins keep each
cell running on a near-24-hour schedule. "Every single cell that we've
looked at in the body has a clock inside of it," says Gillette. "Cellular
timekeeping is a molecular dance, and it's very complicated." Researchers
continue to explore exactly what makes our biological clocks tick. The
answers they find may eventually lead to new treatments for sleep disorders,
jet lag and other health problems.
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