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 off4twice as long as usualand 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 Medicinc, 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.

　　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.

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