Need to stay awake and alert? Small, frequent doses of that old standby, caffeine, will do the trick, researchers report.

Sleep-deprived people who took frequent low-dose caffeine tablets had fewer incidences of "accidental" sleep. And they did better on cognitive tests when compared to those not taking caffeine, the researchers found.

Lead researcher James Wyatt is laboratory director of the Sleep Disorder Center at Rush University Medical Center in Chicago. He said the study was funded by the U.S. Air Force's Office of Scientific Research.

"They were interested in some way to keep pilots awake when they were on long missions," Wyatt said. The Air Force was concerned because during the first Gulf War, pilots used amphetamines and other stimulants to keep awake, he said.

To see how caffeine might work, Wyatt's team studied 16 healthy, young men, aged 18 to 30. The men were put on a 43-hour day, which required them to be awake for 28.5 hours and asleep for 14.25 hours.

This let the researchers keep the subjects awake longer than normal, and also awake and asleep at a variety of body-clock times. "It's like sleep deprivation mixed with jet lag, mixed with shift work," Wyatt said.

Half the men were given low-dose caffeine tablets every hour, during the hours they were awake, and the other men got a placebo, according to the report in the May issue of Sleep. The amount of caffeine given was equal to about one-quarter cup of coffee or half a can of soda, Wyatt said.

This regimen was designed to take into account the two contrasting though interacting processes that control sleep. The first is our body clock -- called the circadian system -- that promotes sleep in a cyclical fashion. The second process is the homeostatic system, which builds the desire for sleep the longer one is awake, Wyatt explained.

According to the researchers, caffeine blocks the receptor for adenosine, a sugar that is involved in the homeostatic drive for sleep.

"Even though caffeine is the most widely used wake-promoting substance in the world, and that it has been used for thousands of years, this is the first time it has been scientifically studied by trying to match it to the body's biology you are trying to counteract," Wyatt said.

What's more, when the men were awake, their cognitive functions were tested every two hours with a series of mental performance tests. Also, every half hour, the men were asked how sleepy or alert they felt.

Using the low-dose caffeine regimen, Wyatt's team was able to match the brain's physiology and negate many of the sleep-deprivation impairments in mental performance. Men receiving caffeine continued to perform well on the tests of cognitive function, compared to the men who didn't get caffeine, Wyatt said.

However, while those taking caffeine were more awake and alert than their counterparts, they reported feeling sleepier. This suggests the effects of caffeine don't replace the beneficial effects of sleep, the researchers said.

For people who have to be awake longer than the standard 16-hour stretch -- such as EMTs, firefighters, medical residents and people in the military -- caffeine can be a "very effective countermeasure to sleep-related impairments in performance," Wyatt said.

Dr. Clifford B. Saper, the James Jackson Putnam Professor of Neurology and Neuroscience at Harvard Medical School, said, "The study does seem to indicate that many cognitive deficits can be minimized by continuous, low-dose caffeine."

However, "every undergraduate has known this from time immemorial," Saper added.

This study supports the role of the homeostatic drive in the cognitive decline associated with sleepiness. However, it doesn't explain the role that caffeine plays in reducing the effects of circadian rhythms on sleep, he said.

"There is no evidence that this caffeine effect is adenosine induced. Rather, the evidence suggests that the caffeine effect may be a generalized arousing one, rather than a specific reversal of an adenosine impact on performance," Saper said.

More information

More on Decaf and Caffeine
More articles on caffeine

Having trouble sleeping? Check with the National Center on Sleep Disorders Research. And the International Food Information Council has lots of information about caffeine.

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