SLEEP: Continual Caffeine Overcomes Sleep Deprivation

SALT LAKE CITY, June 21 - A 200-mg jolt of caffeine every two hours can keep sleepless people functioning at about 100% of normal for 48 hours, according to army researchers here. But that doesn't mean a cup of coffee is enough.

This caffeine-enhanced endurance, induced by 100-mg chewing gum sticks, kept participants in a study going at 75% of normal for up to 70 hours. It contrasted with caffeine-deprived people who become stuporous after 40 hours without sleep and are a menace behind a steering wheel, said a U.S. Army investigator.

"They become non-responsive," Gary Kamimori, Ph.D., of Walter Reed Army Institute of Research in Silver Spring, Md., reported at Sleep 2006, the joint meeting of the Sleep Research Society and the American Academy of Sleep Medicine.

Dr. Kamimori said the caffeine-sleep finding has implications not only for soldiers on a battlefield, but for civilians in jobs that may keep them awake for long periods, while forcing them to focus on relatively monotonous work.

The catch is that a cup of coffee probably won't do the trick. Dr. Kamimori and colleagues reported in a study of 30 soldier volunteers who were randomized to placebo or to a special chewing gum containing 100 mg of caffeine per piece. Estimated caffeine content for various sources are 137 mg per cup of coffee, 47 mg per cup of tea, 46 mg per can or bottle of cola, and 7 mg per serving of chocolate candy. The advantage of the gum, he said, it that it gets into the body in about five minutes, compared with between 20 and 40 for coffee.

The soldiers were allowed to get a full night's sleep and then were kept awake for 70 hours. During that time, they had four two-hour test blocks each night, during which they were required to pay attention to a hand-held device and react within a few seconds when it gave them a signal.

The test blocks were all conducted during the night; during the day, the soldiers were tested on a range of other factors, including mood, emotional intelligence, and decision-making ability. During the test phase, the soldiers got caffeine or placebo gum every two hours.

The key measurement, Dr. Kamimori said, was lag-time-dubbed a "lapse"-between the appearance of the signal and the solder's response. The researchers divided the lapses into three categories:

• An "attentional lapse" lasted between one and five seconds, and the soldier usually noticed it.
• A "responsive lapse" lasted between five and 10 seconds, and the researchers usually had to call the soldier's name to get a reaction.
• A "non-responsive lapses" lasted more than 10 seconds, and the soldier had to be physically shaken before he or she would react.

The number of attentional lapses was significantly lower for the caffeine group on night one, compared with the placebo group, but not on subsequent nights, Dr. Kamimori said. But the reason for that apparent equality was that the number of responsive and non-responsive lapses on the subsequent nights sharply increased for those getting the placebo, compared with those getting caffeine.

Dr. Kamimori noted that although those in the caffeine group had fewer serious lapses, they still had some.

For drivers, air traffic controllers, pilots, and a range of other occupations, prolonged wakefulness could have serious consequences, he said. "Do you want them in a situation where you literally have to shake them awake and they still don't know where they are?"

The few seconds of lapse time may not sound like much, Dr. Kamimori said, but a 10-second lag in reacting to a situation on a battlefield or a busy highway could mean death.

In a related study using the same volunteers, Thomas Balkin, Ph.D., also of Walter Reed, looked at the evidence for a post-caffeine "crash" and found none. Tests of reaction time at midnight on the second and third day-in both cases, 17 hours after the last doses of caffeine-were comparable with those of the placebo group at the same time.

In another study, researchers at the University of California at San Diego showed that the ability to learn suffers dramatically after about 36 hours of wakefulness. The finding is a cautionary tale for generations of students who have pulled successive all-nighters to cram for exams, said Sean Drummond, Ph.D., who is also affiliated with the VA San Diego Healthcare System.

On the positive side, Dr. Drummond said, he and colleagues have previously shown that the brain can compensate for fatigue and continue to learn despite up to 36 hours without sleep; the question was, he said, when that compensation mechanism would start to fail.

Dr. Drummond and colleagues kept 26 healthy participants up for 60 hours and tested them, using functional magnetic resonance imaging (fMRI), as they tried to learn lists of words at several points during the experiment. Sometime after 36 hours, performance dropped off sharply, he said.

"While the brain seems to be able to compensate for that first all-nighter," Dr. Drummond said in an interview, "it does so with a less efficient activation pattern" as evidenced by fMRI. "There is probably some decrease in performance," he said, but by and large the brain finds a way to do the job.

"The second night of sleep deprivation is a wholesale failure to function," he said. "The person is awake, trying, but the brain regions responsible for the given task just can't get going."

Drs. Drummond and Kamimori said their studies are complementary, although they use different methods and attack different aspects of performance. One major difference, Dr. Kamimori said, is that Dr. Drummond's volunteers were tested every few hours, while his soldiers were under the gun constantly.

"We overworked these guys," he said.

Nonetheless, the researchers said, both studies show that lack of sleep has serious side-effects-consequences ranging from failing an exam to dying on a battlefield.