A triple nonfat mocha may taste good, but it's likely the jolt that drives millions of people to fork over three bucks or more for the steaming cup of brown liquid. Between 80% and 90% of North Americans consume caffeine regularly, according to a 2004 review, with an average daily consumption equal to about two mugs of coffee or four 16-ounce bottles of soda.
The habit has become less guilt-inducing recently, with growing evidence that both coffee and tea can fight cancer, heart disease, diabetes, Parkinson's disease and more. Because most people equate these beverages with the caffeine in them, it's tempting to conclude that the stimulant is what gives these wonder drinks their powers.
That may not be the case. Caffeine's effects on health appear to be considerably more nuanced.
On the plus side, the drug does appear to help protect the brain from degenerative disease, give triathletes a nose over the finish line and, for many, keep the brain's gears churning, which is what drives most people to drink it in the first place. But habitual and large doses of caffeine can also stress the heart and interfere with insulin's ability to process sugar. And many of the benefits ascribed to caffeine may be due, in fact, to other chemicals that outweigh caffeine's negative effects.
"As soon as you say coffee, people think caffeine; as soon as you say caffeine, people think coffee," says Terry Graham, a metabolic physiologist at the University of Guelph in Canada, a longtime caffeine researcher who recently organized an international symposium on caffeine and health. Scientists have isolated antioxidants, polyphenols, and micronutrients from coffee and tea, but there have been no long-term studies of how each ingredient, including caffeine, affects the body on its own or within a beverage.
"There are health benefits of coffee that have nothing to do with caffeine," Graham says. In fact, he adds: "There are no health benefits I've ever seen documented for caffeine."
How it works
Anyone who has used a latte to get through an after-lunch meeting -- or ended up with stomach-churning jitters after one too many shots of espresso -- knows that ingesting caffeine has physical consequences. The molecule, which is identical in every beverage that contains it, blocks the action of a naturally produced chemical called adenosine.
Produced in the brain, adenosine normally accumulates during activity and declines during sleep. By the end of the day, it dulls the nervous system, causing drowsiness and a sense of calm and helping the body fall asleep. When caffeine gets in its way, by binding to adenosine receptors throughout the body, the body reacts as if a tiger were about to attack. Blood vessels constrict, causing a rise in blood pressure. The liver releases extra energy-packed sugar into the bloodstream. A rush of excited energy creates a feeling of alertness, even invincibility.
That feeling, to many people, is a good thing. When asked to rate their alertness, many dozens of studies published since the 1960s show that caffeine users report feeling more awake than do people who have been given a caffeine-free pill or beverage, says biological psychologist Peter Rogers, lead researcher of the Dietary Caffeine and Health Study at the University of Bristol in Britain.
In dozens of other studies, he says, caffeinated people have faster response times than noncaffeinated people when pressing a button after seeing a symbol appear on a computer screen. And at a 2005 meeting of the Radiological Society of North American, Austrian researchers reported results of a brain-imaging study that showed caffeine lighting up the brain's short-term memory center.
Studies that link caffeine with mental skills and quick reflexes, however, may simply prove how addictive the drug is, Rogers says. These experiments usually involve regular caffeine-drinkers who abstain for a day or two before the study. Bleary eyed, participants blindly swallow either a caffeine-laced pill or drink, or a caffeine-free placebo. Those who randomly get their usual daily dose, not surprisingly, do better on the tests.
"What we find is that if you take caffeine away from caffeine drinkers, they perform worse than when they get caffeine and they perform worse than people who don't normally get caffeine," Rogers says. "The traditional interpretation ... is that people do better on caffeine and that caffeine does make you more alert."
When people who are normally caffeine-free get caffeine, however, some studies show only a much smaller mental boost, while others show no boost at all, says Rogers, who published a review of related studies in the journal Psychopharmacology in 2005. It may be withdrawal that makes people falter, he says, not caffeine that makes them sharper. If they're not already coffee drinkers, taking up the habit won't make help.