共用题干第二篇Late-night DrinkingCoffee

共用题干

第二篇

Late-night Drinking

Coffee lovers,be careful.Having a quick "pick-me-up" cup of coffee late in the day will interrupt your
sleep. As well as being a stimulant（兴奋剂）,caffeine interrupts the flow of melatonin（褪黑激素）,the
brain hormone that sends people into a sleep.
Melatonin levels normally start to rise about two hours before bedtime.Levels then peak between 2 am
and 4 am , before falling again. " It ’s the neurohormone（神经激素）that controls our sleep and tells our
body when to sleep and when to wake,"says Maurice Ohayon of the Stanford Sleep Epidemiology Research
Center at Stanford University in California. But researchers in Israel have found that caffeinated coffee halves
the body’S levels of this sleep hormone.
Lotan Shilo and a team at the Sapir Medical center in Tel Aviv University found that six volunteers slept
less well after a cup of caffeinated coffee than after drinking the same amount of decaf（脱咖啡因咖啡）.On
average,subjects slept 336 minutes per night after drinking caffeinated coffee,compared with 415 minutes
after decaf. They also took half an hour to drop off,twice as long as usual.
In the second phase of the experiment,the researchers woke the volunteers every three hours and asked
them to give a urine（尿）sample.Shilo measured concentrations of a breakdown product of melatonin.The
results suggest that melatonin concentrations in caffeine drinkers were half those in decaf drinkers.In a paper
accepted for publication in Sleep Medicine,the researchers suggest that caffeine blocks production of the
enzyme（酶）that drives melatonin production.
Because it can take many hours to eliminate caffeine from the body.Ohayon recommends that coffee
lovers switch to decaf after lunch.

Which of the following tells us how caffeine affects sleep? A:It blocks production of the enzyme that stops melatonin production. B:It interrupts the flow of the hormone that prevents people from sleeping. C:It halves the body’s levels of sleep hormone. D:It stays in the body for many hours.