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  3. Late-night Drinking Coffee lovers beware. Having a quick "pick-me-up" cup of coffeel late in the day will play-havoc with yo

Late-night Drinking Coffee lovers beware. Having a quick "pick-me-up" cup of coffeel late in the day will play-havoc with yo

admin2012-07-29  88
问题                             Late-night Drinking
    Coffee lovers beware. Having a quick "pick-me-up" cup of coffeel late in the day will play-havoc with your sleep. As well as being a stimulant, caffeine interrupts the flow of melatonin, 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 a. m. and 4 a. m. , before falling again. "It’s the neurohormone 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. 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-and jigged around in bed twice as much.
    In the second phase of the experiment, the researchers woke the volunteers every three hours and asked them to give a urine 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 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? ______
选项 A、Caffeine blocks production of the enzyme that stops melatonin production.
B、Caffeine interrupts the flow of the hormone that prevents people from sleeping.
C、Caffeine halves the body’s levels of sleep hormone.
D、Caffeine stays in the body for many hours.
答案C
解析 第二段的第三个句子谈到，“控制我们睡眠的是神经激素”，而这一段的最后一个句子告诉我们“含咖啡因咖啡能使这种睡眠激素减半”。这正是咖啡因影响睡眠的原理。
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