第3篇 Late-night drinking
Coffee lovers beware. Having a quick “ pick-me-up” cup of coffee late in the day will play havoc with you sleep. As well as being a stimulant, caffeine interrupts the flow
of melatonin, the brain hormone that send 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 Epidemiklogy 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 twice as much..
In the second phase of the experiment, the researchers woke the volunteers evey three hous and asked them to give a urine sample. Shilo measured concentrations of abreakers
were half those in decaf drinkers. 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 the 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.
练习：
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 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 sleep hormone.
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 evidence that the subjects took half an hour to fall asleep.
4. What does the experiment mentioned in paragraph in paragraph 4 prove?
A) There are more enzymes in decaf drinkers’ urine sample.
B) There are more melatonin concenrrations 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.
