Tactics to Boost Alertness May Benefit Night Workers

A novel high-frequency, low-dose caffeine regimen can counteract performance decrements linked with extended bouts of wakefulness, a study in the May issue of Sleep shows.

The findings may benefit resident physicians, military personnel, emergency workers, and others who must stay awake—and highly alert—more than 16 hours at a time, said James Wyatt, Ph.D., who led the research team. Wyatt is an assistant professor of psychology at Rush University Medical Center in Chicago.

Wyatt and colleagues at Harvard Medical School studied 16 healthy young-adult men who spent 29 consecutive days in laboratory apartments free of time cues at the Brigham and Women's Hospital in Boston. The men lived on 42.85-hour “days” consisting of 28.57-hour wake episodes and 14.28-hour sleep episodes.

The researchers crafted the 42.85-hour cycle to permit scheduling of wake and sleep episodes across a range of circadian phases. The long waking period, they noted, mirrors that of resident physicians on on-call shifts and of pilots on long-haul combat missions. The U.S. Air Force, which funded the study, specified that all study subjects be men.

To minimize the influence of the light/dark cycle on body rhythms, the researchers kept room lights dim throughout the men's waking hours. They required the men to remain in bed in near darkness during scheduled sleep times.

Every hour during the extended wake periods, eight men ingested one capsule of caffeine (0.3 mg per kg per hour), and eight took a placebo. For an average adult man, Wyatt said, one capsule provides the equivalent of about a quarter cup of coffee.

Wyatt and his colleagues monitored all sleep episodes polysomnographically and gave the men a battery of tests to assess mood, cognitive performance, and subjective sleepiness. They also measured levels of the hormone melatonin, which serves as a marker of time on the body clock.

The men who took caffeine performed almost as well on various tests after being awake 28 hours as they did after being awake for only two hours, Wyatt reported. They far outperformed the placebo users. They also dozed off far less often in waking hours than did the placebo users. The wake-promoting effects of caffeine, Wyatt cautioned, do not replace the restoration sleep provides. Nonetheless, consuming half a cup of coffee every two hours may help people who must stay awake much longer than usual and stay more alert than they otherwise would. A small amount of caffeine provides this benefit, Wyatt said, without causing the tremulousness or nervousness larger doses frequently induce.