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Late-Night Drinking

Coffee lovers beware. Having a quick “pick-me-up” cup of coffee1 late in the day will play havoc with2 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 am and 4 am, before falling again3. “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 caffcinated 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 decal. On average, subjects slept 336 minutes per night after drinking caffeinated coffee, compared with 415 minutes after decal. They also took half an hour to drop off4 - twice as long as usual - and jigged around5 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 suggest6 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.

1. The author mentions “pick-me-up” to indicate that

A melatonin levels need to be raised.

B neurohormone can wake us up.

C coffee is a stimulant.

D decaf is a caffeinated coffee.

2. Which of the following tells us how caffeine affects sleep?

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.

3. What does paragraph 3 mainly discuss?

A Different effects of caffeinated coffee and decaf on sleep.

B Different findings of Lotan Shilo and a team about caffeine.

C The fact that the subjects slept 415 minutes per night after drinking decaf.

D The proof that the subjects took half an hour to fall asleep.

4. What does the experiment mentioned in paragraph 4 prove?

A There are more enzymes in decaf drinkers’ urine sample.

B There are more melatonin concentrations in caffeine drinkers’ urine sample.

C Decaf drinkers produce less melatonin.

D Caffeine drinkers produce less sleep hormone.

5. The author of this passage probably agrees that

A coffee lovers sleep less than those who do not drink coffee.

B we should not drink coffee after supper.

C people sleep more soundly at midnight than at 3 am.

D if we feel sleepy at night, we should go to bed immediately.

答案与题解 :

1. C pick-me-up指提神饮料，也就是一种剌激物，在这篇文章里具体指咖啡。所以，答案应选 C。

2. C 第二段的第三个句子谈到，“控制我们睡眠的是神经激素”，而这一段的昀后一个句子也告诉我们“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。

3. A第三段涉及的是一个实验，这个实验的目的是测试含咖啡因咖啡和脱咖啡因咖啡对睡眠的影响，该段主要谈论的是这个实验的结果。

4. D 第四段是第三段实验的继续，是该实验的第二个阶段。研究人员通过对志愿者尿样进行化验发现，咖啡因摄入者体内的褪黑激素仅为非咖啡因摄入者的一半。褪黑激素就是睡眠激素，所以，答案应该选 D。

5. B 文章的结尾谈到， “Ohayon建议爱喝咖啡的人午饭后应该换喝脱咖啡因咖啡”。另外，整个文章都在探讨咖啡因影响睡眠的机理，所以，作者大概会同意“晚饭后不应该喝咖啡”的说法。选项 A是一个全称判断，这等于说“所有喜欢喝咖啡的人都比不喝咖啡的人睡觉少”。这不一定，因为如果咖啡适量，喝咖啡的时间适当，咖啡不会影响睡眠。所以，作者可能不会同意这种说法。根据文章第二段第二个句子，选项 C是错的。根据文章第二段的第一个句子，我们体内褪黑激素 (睡眠激素 )的浓度在我们上床时间前两个小时开始上升，而这个时候我们会开始有困意。反过来说就是，人们并非一有困意就睡觉。所以，选项 D不是答案。

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