From VOA Learning English, this is the Health & Lifestyle report.
Caffeine is the most widely used
drug in the world. Many people drink coffee or tea to help them wake in the
morning. And many others drink caffeine throughout the day to prevent
sleepiness.
So, it is no surprise that if you get too much caffeine
before bedtime, it can keep you awake. It turns out that interrupting
your sleep is bad for your health on many levels, including the cellular level.
A new study explains how interrupted sleep can affect
your mental and physical health. The study also explores how poor sleep can
affect the cells in your body.
Researchers from the United States and the United Kingdom
have joined from across the pond to investigate this issue.
The investigators are from the University of Colorado,
Boulder in the U.S. and the Medical Research Council Laboratory of Molecular
Biology in Cambridge, England. They found that caffeinated drinks taken up to
three hours before expected bedtime can delay normal sleep times by as much as
40 minutes.
The amount of caffeine that disrupted sleep was
equal to about two shots of espresso.
Kenneth Wright is head of the Sleep and Chronobiology
Laboratory at the University of Colorado Boulder. Mr. Wright warns some coffee
drinks sold in coffee shops usually contain more caffeine than that.
"This particular finding tells us that the timing of
sleep and wakefulness will be pushed later because of an effect on the
(biological) clock, not just promoting wakefulness chemicals in the
brain."
This is no surprise. Scientists have known for a long time
that caffeine keeps you awake. Caffeine affects the chemicals in the brain that
control wakefulness. Caffeine also blocks chemicals in the brain that promote,
or cause you to sleep.
And interrupted sleep is not good for you.
Not getting enough sleep can affect a person’s mood.
It also disrupts the body’s natural sleep-wake cycle called the circadian
rhythm. Your body’s circadian rhythm is found in cells throughout
the entire body.
So, when caffeine disrupts your circadian rhythm, it
affects hormone production and the re-growth of new cells in the human body.
And this can play a role in many health problems – from obesity to diabetes to
cancer.
The experiment
To look into caffeine's effect on the circadian rhythm,
or circadian clock, researchers first noted the sleep-wake cycles of five
healthy volunteers.
The study lasted 49 days. Researchers gave the
participants 200 milligrams of caffeine a few hours before bed. Two hundred
milligrams of caffeine is about the amount found in two shots of espresso. Then
the researchers noted how long it took the volunteers to fall asleep.
The volunteers were also exposed at night to
bright light, which is also known to disrupt sleep. Caffeine, however,
interrupted the circadian clock, and patterns of sleep, more so than
bright light did. Caffeine affects the production of melatonin, the
sleep-producing hormone.
When a person’s circadian rhythm is disrupted, sleeping
and eating patterns are thrown off. A disrupted circadian rhythm increases the
chance of heart disease, obesity and mental illnesses such as depression
and bipolar disorder. Bipolar disorder is a disease of the brain where
people experience extreme highs and extreme lows.
But caffeine’s effect on the body is not all bad.
Mr. Wright says people could use caffeine to help their
body’s clock, for example, when they travel.
"Another example of an implication of our findings
is we may be able to use caffeine to help shift our clocks westward when we're
traveling across many time zones. In this case here, caffeine may help us adapt
to jet lag much faster."
The scientists published their findings in the journal Science
Translational Medicine. The scientists also give some common sense advice
-- people who want to wake up earlier in the morning might want to avoid that
nighttime cup of caffeine.
And that’s the Health & Lifestyle report.
I’m Anna Matteo.
Do you drink caffeine before bedtime and does
it affect your sleep or mood? Let us know in the comments section and on our Facebook
page.
Jessica Berman reported this story from Washington,
D.C. for VOA News. Anna Matteo adapted it for Learning English. Caty Weaver was
the editor.
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Words in This Story
interrupt
– v.
to cause (something) to stop happening for a time
caffeine
– n.
a substance that is found especially in coffee and tea and that makes you feel
more awake
across
the pond – idiomatic
phrase : that means on the other side of the Atlantic Ocean. It is used to
refer to the United States or the United Kingdom depending on the speaker's
location
disrupt – v. to cause
(something) to be unable to continue in the normal way
circadian
rhythm – n.
daily rhythmic activity cycle, based on 24-hour intervals, that is exhibited by
many organisms
promote
– v.
to help (something) happen, develop, or increase
hormone – n. a natural
substance that is produced in the body and that influences the way the body
grows or develops
depression
– n.
a serious medical condition in which a person feels very sad, hopeless, and
unimportant and often is unable to live in a normal way
bipolar
disorder – n.
any of several psychological disorders of mood characterized usually by
alternating episodes of depression and mania —called also manic depression,
manic-depressive illness
DG
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