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The conclusion of the three-part story on how sleep
impacts health.
FOOD
intake can also affect body clocks—and vice versa. The
movement of glucose and nutrients through the
bloodstream to organs affects appetite, digestion and
metabolism. Travelers frequently encounter stomach and
digestive difficulties when crossing time zones, for
example, because food intake is in conflict with the
time-keeping molecules in the body’s digestive system.
“When
you’re a shift worker and displace your sleep, you also
displace your feeding schedule,” says sleep researcher
Eve Van Cauter, a professor of medicine at the
University of Chicago. The liver, pancreas and digestive
system are not expecting food at the time that they’re
getting it.
Sleep
schedules that buck the body’s natural circadian rhythms
can disrupt insulin production and other hormones that
are important to weight control, Van Cauter says. In a
series of studies, she found that sleep-deprived adults
produce more ghrelin, a hormone that promotes hunger,
and less leptin, a hormone that suppresses appetite.
Thus, the brains of tired people are sending out
compelling messages to eat—especially foods that are
starchy, sweet and high-carb.
Accordingly, people who sleep less may have more trouble
keeping their blood sugar stable. In one of Van Cauter’s
studies, healthy young men were restricted to four hours
of sleep per night for six consecutive nights and were
found to have blood test results for insulin sensitivity
so abnormal they almost matched those of diabetics.
Other
research is exploring the effects of sleep and shift
work on neurotransmitters called orexins. These brain
chemicals have unique, dual roles, making sure humans
are alert when hungry to maximize food-seeking behavior.
After a
big meal, fast-rising glucose levels in the body switch
off orexin neurons, often making people feel
sleepy—possibly an evolutionary response signaling
humans to conserve energy after eating. “There is wiring
in our brains that links feeding and being awake,” Van
Cauter says.
Thus,
eating at
midnight and sleeping at
noon
could lay the groundwork for the obesity, diabetes and
heart disease seen more commonly in night workers.
Moreover, as people age, they spend less time each night
in phases of deep sleep. Van Cauter’s research team is
investigating whether this poorer-quality sleep may
contribute to a variety of ailments in old age.
Preventing the damage
FOR
people such as registered nurse Liberty Bunag and UPS
truck driver Dennis Corrigan—and for society as a
whole—night-shift work is a reality. “Our entire
transportation infrastructure would break down if those
trucks decided to use the roads during the day,” says
Dr. Charles Czeisler, director of the division of sleep
medicine at
Harvard
Medical School.
That’s
why, ultimately, scientists want to prevent the damage
from shift work or insufficient sleep.
It’s not
easy, however, to tease apart the biological effect of
disrupted circadian rhythms from other factors that may
influence night-shift workers’ health, such as poor
diets, stress and lack of exercise. Many diseases, such
as cancer and heart disease, are also influenced by risk
factors that have nothing to do with occupation.
Moreover, individuals differ in how they cope with
circadian rhythm disruption. As many as 10 percent adapt
well, but 15 percent to 20 percent simply can’t tolerate
staying awake all night, according to Czeisler. The
remainder cope, but with difficulty.
Sleep
researchers have devised compensation tactics, such as
the use of bright lights and melatonin supplements, to
help night-shift workers remain alert on the job and
sleep better after the shift. But the research on the
body’s molecular clocks may lead the way to better
therapies, says Paolo Sassone-Corsi, chairman of the
department of pharmacology at the University of
California, Irvine.
Identifying the molecular clocks that affect cell
division, for example, may point the way to treatments
to prevent cancer.
In a
paper published in December in the journal Nature,
Sassone-Corsi found that a single amino acid activates
the genes that regulate circadian rhythms. This chemical
switch could perhaps be manipulated by a medication of
some sort to restore circadian rhythms that have gone
awry.
“If we
can explain how these molecules work, we can get
targets” for potential therapies, he says. “We cannot
beat the system, but we can work on it.”
For now,
however, researchers and sleep doctors alike implore
people to show a little respect for slumber.
“People
think of sleep as a waste of time,” Sassone-Corsi says.
“But it’s essential. A correct sleep-wake cycle is as
important to health as any other thing in our lives.”
*****
How to cope with shift work
SLEEP
experts suggest various ways to cope with unusual work
and sleep schedules.
Regular
hours:
Keep the same sleep schedule on days off from work.
Strategic napping:
Studies show naps of 20 minutes to two hours—either just
before a shift or during a shift—can improve alertness
and performance at work.
Bright
light:
Exposure to bright lights during the first half of a
shift may help fight fatigue later in the shift.
Light
restriction:
Avoiding bright lights in the morning (such as by
wearing sunglasses on the way home and sleeping in a
very dark room) can help night-shift workers sleep
better during the day.
Melatonin:
Supplements can promote daytime sleep when taken an hour
or two before bedtime.
Modafinil:
This medication, brand name Provigil, was approved in
2004 for the treatment of shift-related sleep disorder.
Taken just before a shift, it can enhance alertness at
night, studies have shown.
Caffeine:
Caffeine
has been shown to counteract drops in performance levels
at night. |
