"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.
In the U.S., 87 percent adults and 76 percent of children consume some caffeine on a daily basis. That's up from 82 percent of adults and 43 percent 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.