Most adults need around eight hours of sleep per night, on a regular basis, to feel rested and awake during the day. Any change to this routine disrupts the delicate balance between two opposing but interacting processes that regulate sleep: the circadian and the homeostatic.

The circadian rhythm operates like a 24-hour internal clock. As part of this cyclical process, the body releases hormones, such as melatonin, to help us know when it’s time to fall asleep and wake up. The homeostatic system, on the other hand, regulates sleep by building up a need for sleep—the longer one is awake, the greater the need for sleep.

Many people rely on caffeine to wake them up in the morning and perhaps to provide a little boost in the afternoon. Research suggests that caffeine works by blocking the uptake of adenosine, a brain chemical that induces sleep and is part of the homeostatic system. If this is the case, it means caffeine promotes wakefulness and alertness by interacting with the homeostatic system.

Most previous studies, however, have not accounted for the roles of both the circadian and homeostatic systems in the regulation of sleep. But according to a new study in the May 2004 issue of the journal SLEEP , small frequent doses of caffeine effectively counteract the detrimental effects of extended wakefulness—suggesting that caffeine enhances wakefulness and performance by interacting with the homeostatic system.

About the Study

This study included 16 healthy normal-sleeping men between the ages of 18 and 30. As part of the study, the men lived in private suites with regulated lighting and no obvious indications as to time of day. For the first three days the men followed a normal 24-hour cycle: staying awake for 16 hours during the day, and then sleeping for eight hours at night. But then researchers rescheduled the participants to a 43-hour cycle consisting of 29 hours of wakefulness and 14 hours of sleep.

Throughout the 29-day study period, participants had to remain awake during the scheduled wake episodes and stay lying down in bed during the scheduled sleep episodes. While awake, the participants took either a placebo or caffeine-containing capsule every hour until one and a half hours before bedtime. The caffeine capsule contained 0.3 milligrams of caffeine per kilogram body weight—roughly two ounces of coffee.

The researchers assessed mood, sleepiness, and cognitive performance (i.e., short-term memory, mathematical reasoning) using a variety of tests. Throughout the day and night they also monitored eye movement and unintentional sleep onsets. Core body temperature was recorded each minute and blood samples were obtained every hour.

The Findings

The researchers found that the participants’ circadian clocks were unable to adjust to the imposed 43-hour cycle. Average body temperatures and blood melatonin levels showed that participants in both groups maintained circadian cycles of approximately 24.3 hours.

Participants in the caffeine group functioned better on the cognitive performance tests and were less likely to fall asleep during the day than those receiving the placebo. The researchers reasoned that the gradual increase in caffeine supply to the brain counteracted the accumulating levels of adenosine, released as part of the homeostatic drive for sleep.

While caffeine helped participants stay awake for extended periods, it also prevented them from completing a full transition to sleep. Because they didn’t sleep as well, participants in the caffeine group actually felt sleepier throughout the day, than those in the placebo group.

How Does This Affect You?

This study shows that consuming small but frequent amounts of caffeine can help counteract the detrimental performance effects associated with sleep deprivation. Rather than having 16 ounces of coffee in the morning and again in the afternoon, for example, this study suggests spreading it out into 16 two-ounce servings. This may be a bit unrealistic—and perhaps unnecessary—for most of us, but for people who need to be awake and alert over extended periods of time, such as medical residents, truck drivers, and military personnel, these findings may have significant implications.

And for the rest of us who just need a little help to make it through the day, it may still make sense to distribute our morning jolt of caffeine more evenly throughout the day. Of course, in an ideal world, we would simply get all the sleep we need and drink coffee purely for the pleasure of it. But until such a world exists it’s good to know that caffeine will help us through...time for some more coffee.