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The Stay-Alert Secret of Caffeine

Caffeine Might Show the Way to Better Sleep, Researchers Say
WebMD Health News

April 21, 2005 -- Just in time for final exams, scientists have figured out how caffeine keeps the brain buzzing when it's due for sleep.

"We knew that coffee kept us awake. Now we know why," says researcher Robert Greene, MD, PhD, in a news release.

The finding comes from lab tests with rats given a caffeine-like chemical. The results may shed new light on sleep problems.

"If we can understand better some of the factors involved in what makes us normally fall asleep, we can start to understand what might be going wrong when we don't," says Greene, a psychiatry professor at the University of Texas Southwestern Medical Center in Dallas.

Fighting Off Sleep

Caffeine blocks a brain chemical called adenosine, which prompts feelings of drowsiness, Greene reports in the April 21 issue of Neuron.

Ordinarily, brain cells release adenosine when they're overworked. Brain cells have a demanding job. They have to run the body, process information, and communicate with other brain cells constantly. Sooner or later, they need a break. That's when the brain starts pumping out more adenosine.

"More and more adenosine is released and feeds back onto the cells to quiet them down," says Greene. "It's like telling them, 'You guys have worked too hard. Take it easy; refresh yourselves.'"

When caffeine thwarts adenosine, go-to-sleep signals get derailed until caffeine's effects wear off.

Caffeine Sources

In the U.S., 87% adults and 76% of children consume some caffeine on a daily basis. That's up from 82% of adults and 43% of children (aged 6-17) in 1977.

Those numbers appeared in January's Journal of the American Dietetic Association, which named coffee as America's No. 1 caffeine source.

Caffeine is also found in tea, some soft drinks, and (to a lesser degree) chocolate. Herbal supplements, medications, energy drinks, and caffeinated water are other sources.

People may not realize how much caffeine they're getting, researchers reported in the Journal of the American Dietetic Association. They say caffeine must be listed as an ingredient but that Nutrition Facts labels needn't specify the amount, and that herbal caffeine sources might not be listed as an active ingredient.

A quick guide to caffeine levels:

  • 8 ounces of brewed coffee: 135 milligrams
  • 8 ounces of tea: 50 milligrams
  • 12 ounces of Coca-Cola: 34.5 milligrams
  • 12 ounces of Diet Coke: 46.5 milligrams

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