Late-Night Drinking

Coffee loversbeware.Having a quick"pick-me-up"cup of coffee late in the day willplay havoc with your sleep .As well as being a stimulant,caffeine interruptsthe flow of

melatonin,the brainhormone that sends people into a sleep.

Melatonin levelsnormally start to rise about two hours before bedtime. Levels then peak be-tween2 am and 4 am,before falling again."It's the neurohormone that controlsour

sleep tells our bodywhen to sleep and when to wake,"says Maurice Ohayon of the Stanford SleepEpidemiology ResearchCenter at Stanford Universityin California.But

researchers in Israelhave found that caf feinated coffee halves the body's levels of this sleephormone.

Lotan Shilo and ateam at the Sapir Medical Center in Tel Aviv University found that sixvol-unteers slept less well after a cup of caffeinated coffee than after drinkingthe

same amount ofde-caf. On average,subjects slept 336 minutes per night after drinkingcaffeinated coffee,compared with 415 minutes after decaf. They also took halfan hour

to drop offtwice aslong as usual-and jigged around in bed twice as much.

In the second phaseof the experiment,the researchers woke the volunteers every three hours andasked them to give a urine sample.Shilo measured concentrations of a

breakdown product ofmelatonin .The results suggest that melatonin concentrations in caffeinedrinkers were half those in decaf drinkers .In a paper accepted for publication

in SleepMedicine,the researchers suggest that caffeine blocks production of the enzymethat drives melatonin production.

Because it can takemany hours to eliminate caffeine from the body,Ohayon recommends that coffeelovers switch to decaf after lunch.Which of thefollowing tells us how caffeine affects sleep?

A.Caffeine blocksproduction of the enzyme that stops melatonin production.

B. Caffeineinterrupts the flow of the hormone that prevents people from sleeping.

C. Caffeine halvesthe body's levels of sleep hormone.

D. Caffeine stays inthe body for many hours.