Leaning on Caffeine

If you're depending on coffee to keep you awake, make sure you know what you're doing.

By Carlin Flora, published on July 26, 2004 - last reviewed on October 13, 2005

Finishing a term paper? Working the second shift? Driving late into the night? Many of us grab hold of a coffee mug as if it were a life raft in The Struggle To Stay Awake.

Caffeine is certainly America's stimulant of choice -- 80 to 90 percent of us take it daily to foster alertness. Around the world java percolates and teabags simmer in millions of homes each morning.

Yet scientists still do not know exactly how caffeine delivers that dependable jolt. A group of Harvard Medical School researchers has gotten closer to the answer. What's more, they propose a more effective and novel way to lean on caffeine when we're drowning in drowsiness.

Instead of quaffing one giant emergency venti latte, you're better off taking frequent sips of small servings of coffee. That way, the caffeine can work more naturally against the body's drive for sleep.

This information didn't come cheaply. It required a certain amount of human sacrifice. Sixteen men were sequestered for a month and kept on a brutal schedule that dictated awake periods of 28.57 straight hours -- similar to those required of medical residents and military and emergency services personnel.

Rooms were free of external cues such as clocks, in order to throw off the men's circadian system, the body's internal clock that promotes sleep rhythmically in response to signals such as sunlight. Meanwhile, the conditions stretched to its limit another physiological system that also governs sleep, the homeostatic system. This system drives sleep in a cumulative rather than cyclical manner, so that the longer one is awake, the more it pushes for sleep.

When they awoke, and once an hour afterwards, the men were given a caffeine pill, roughly the equivalent of two ounces of coffee, or an identical-looking dummy pill. The caffeinated group performed better on cognitive tests and didn't accidentally nod off as often as their placebo counterparts. "There is no match for the restorative effects of sleep," says Charles Czeisler, professor of sleep medicine at Harvard. "We're not recommending that people stay up, but we're excited to have found a novel way to avoid many of the adverse consequences of an extended bout of wakefulness."

A more effective way to fight off sleep is good news to the approximately 8 million people in the U.S. who regularly work at night and attempt to sleep by day. Tiredness reduces productivity and increases the risk of accidents; sleep loss is implicated in more than 56,000 motor vehicle crashes each year. The environmental disaster resulting from the grounding of the oil tanker Exxon Valdez was ultimately blamed on the crew's sleep deprivation.

Just as they suspected, Czeisler and his colleagues concluded that caffeine works to blunt the homeostatic drive for sleep. Caffeine blocks the receptor for adenosine, a critical chemical messenger involved in the push for sleep.

But it's most effective if administered in parallel with growing pressure from the homeostatic system, to counter the accumulation of adenosine. "By modestly increasing caffeine in the system as the drive for sleep was rising, we could attenuate the increase of adenosine," Czeisler says.

What about those of us who are not piloting oil tankers or fighting forest fires, but who wake up groggy after a late night on the town? Using caffeine in a way more relevant to our biology still makes sense.

Says Czeisler: "The method could certainly ward off an afternoon crash, but it must be applied with good personal judgment." Because caffeine stays in the body for about 6 or 7 hours, regular doses late in the day could have an adverse impact on sleep.

Once caffeine hits the bloodstream, the brain and body enter an excited state: the mind is quicker and memory improves (though not necessarily complex reasoning). But once the effect wears off, fatigue sets in with a vengeance to correct for that prolonged state of heightened alertness. Caffeine sets off a host of reactions: heart rate increases, blood vessels constrict (which is why it is a useful treatment for headaches) and breathing improves as air passages relax.

Moderate caffeine intake produces no health risks. However, because caffeine reduces blood flow to the brain, it could precipitate panic attacks in some people; it spurs irritability and "jitters" in others. Pregnant women should limit caffeine intake; it may lower infant birth weight and delay development.

Be conservative when measuring out your small doses. Czeisler warns that the ubiquitous Starbucks and Dunkin' Donuts brands pack more caffeine than coffees of yore. Not that there is any danger of a shortage: "Coffee is second only to oil in global trade," he says. "It is the most widely-used pharmaceutical in the world."