What is it about coffee?
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.
It could, however, hurt their hearts. Studies show an average blood pressure increase of 4/2 millimeters of mercury (mmHg) after taking caffeine, according to a 2004 review of research published in the journal Psychosomatic Medicine. That small spike won’t matter much for most people, but it could exacerbate the condition of someone on the edge of heart problems, says Jim Lane, a psychophysiologist at Duke University Medical Center in Durham, N.C., who has extensively studied the relationship between caffeine, stress and health.
People report feeling more stressed out while caffeinated, Lane says, with good reason. In a study published in the journal Psychosomatic Medicine in 2002, he found that, after taking a caffeine pill equivalent to the amount in four or five cups of coffee, people showed an average 32% rise in the stress hormone adrenaline and a 3-millimeter rise in blood pressure. These effects lasted throughout the day after people took caffeine. A 5-millimeter rise in blood pressure leads to a 34% increase in the risk of stroke and a 21% increased risk of coronary heart disease, according to a review of nine large studies, and each millimeter rise adds an equivalent amount of risk, Lane says.
His studies also show that taking on difficult, mind-bending math problems while caffeinated produces more stress than either caffeine -- or math -- alone. Chronically high levels of stress can damage the blood vessels, kidneys and heart. “Caffeine exaggerates the effects of stress on the body as if the stress were worse,” he says. “It doesn’t just add stress, it multiplies.”
Studies show a slight drop in blood pressure when people stop drinking coffee for a few days, Lane says, but scientists have yet to prove a link between caffeine and cardiovascular problems. “It is consistently reliable that caffeine raises blood pressure, and we know that higher blood pressure is associated with a greater risk of heart disease,” he says. “To really test that scientifically, you would have to take a large number of people, assign them to drink coffee every day or never drink coffee, and follow them for 5 to 10 years. No one is going to do that study.”
A number of long-term studies have, however, compared the health of people who choose to guzzle coffee and tea with those who avoid the stuff. And those studies are turning up perplexing results that contradict the isolated effects of caffeine.
Some data, for example, suggest that drinking coffee might help prevent heart disease. In a study published in February in the American Journal of Clinical Nutrition, for example, scientists from the City University of New York and State University of New York Health Science Center at Brooklyn followed more than 6,500 healthy adults for nearly nine years. In people older than 65, results showed, those who drank four or more cups of coffee a day were about half as likely to die from cardiovascular disease as their coffee-free peers. Similar studies have found similar trends. Coffee contains thousands of compounds that might be responsible for such benefits, but polyphenols, similar to the healthful compounds found in chocolate and red wine, as well as antioxidants are the most likely candidates.
Several large studies have linked large daily doses of coffee with lower rates of Parkinson’s disease, as well. One theory is that regular caffeine consumption makes the brain more sensitive to adenosine, which has been shown to help protect the brain from mini-strokes caused by oxygen and sugar deprivation, Rogers says. Another possibility is that people with less addictive personalities have a genetic profile that makes them more likely to develop the degenerative brain disease. It’s also possible that people who drink coffee tend to have healthier lifestyles in some other way. Only men seem to get the brain protection from caffeine, and estrogen may work against caffeine’s brain-buffering effects in women.
Many painkillers also contain caffeine, which can ease the pain of migraine headaches by dilating blood vessels in the brain. And coffee drinking has also been linked to lower rates of liver cancer, Type 2 diabetes and gout, among other ills. However, scientists warn, correlations such as these don’t prove that the drink itself (or any ingredient in it) is responsible for the protective effect. In some cases, the benefits probably come from other ingredients.
Diabetes is a perfect example. At least six large-scale, long-term studies have shown that men who drink 7 to 10 cups of coffee a day are 50% to 80% less likely to develop Type 2 diabetes than non-drinkers. In one of the largest such studies, which included more than 125,000 healthy people, women who drank at least 6 cups of coffee a day were 29% less likely to develop the disease than women who didn’t drink coffee. Results were published in 2004 in the journal Annals of Internal Medicine. More recent analyses show that both regular coffee and decaf are equally protective, Graham says.
Pure caffeine, in fact, can exacerbate the symptoms of diabetes. Graham and colleagues have done studies in which they controlled levels of sugar and insulin in their patients’ blood. Insulin is the hormone that allows cells to remove sugar from the bloodstream, and diabetics can’t make enough of it. These experiments show that a given amount of insulin can process 30% to 40% less sugar when caffeine is around, Graham says. In other words, when you drink caffeine and then eat some carbs, the level of sugar in your blood goes up, forcing the production of more insulin to compensate for the extra sugar.
And once sugar levels are up, they tend to stay up, Graham says, particularly in people who are obese or diabetic. In some of his studies, participants abstain from caffeine for two days. Then, on the morning of the study, they take a pill containing 300 to 350 milligrams of caffeine (the amount in three standard cups of coffee) before eating or drinking a carbohydrate-rich meal or drink.
If people are at a healthy weight, results show, they can usually maintain stable sugar levels -- by making more insulin to compensate for caffeine’s sugar-spiking effects. People who are overweight or diabetic, on the other hand, often can’t produce more insulin, and their blood sugar rises. Even when they eat a meal three hours later, the effect of the caffeine is the same.
“It has an extended response,” Graham says, “and it’s a response that one would interpret as far from optimal for health.”
A boost for athletes
Caffeine is a common ingredient in diet pills, because it forces fat cells to release fat into the blood, but that does not translate into fat burning or weight loss -- common myths with no evidence to back them up.
In serious athletes, though, caffeine can enhance both speed and endurance by helping muscles contract with slightly more force. In a 1998 study, for example, Graham and colleagues challenged nine runners to push themselves to exhaustion on a treadmill at a strenuous pace. Before each of five efforts and without knowing what they were swallowing, runners took a caffeine capsule, a placebo capsule, caffeinated coffee, decaf coffee or decaf with caffeine added (to see if decaffeination was altering the coffee in ways other than simply removing caffeine).
On average, the athletes were able to run for about 32 minutes in both non-caffeinated trials. With a boost from caffeine pills and caffeinated decaf, they ran 7 to 10 minutes longer, Graham reported in the Journal of Applied Physiology. Oddly enough, the regular coffee had no effect, even though blood tests showed that there was just as much caffeine in the runners’ bodies in all caffeinated trials.
“We kept testing more subjects because we didn’t believe the data,” Graham says.
Caffeine in the form of sports drinks, soda or pills can improve endurance, he says, but coffee doesn’t work. “Our only conclusion is that there must be factors in coffee that work in the opposite fashion.” Some studies suggest that a class of antioxidants called chlorogenic acids might have something to do with it, he adds.
Still despite that research, caffeine probably won’t help the average Joe Treadmiller. A 1991 study in France found that even though highly trained swimmers sprinted faster in the 100-meter freestyle after taking caffeine, the stimulant didn’t increase the speed of untrained swimmers. Only when muscles are pushed past the point of exhaustion, Graham says, does caffeine kick in to give them extra oomph.
No verdict yet
Despite evidence that caffeine causes bones to leach calcium and fears that caffeine can cause early contractions or make it hard to conceive, most scientists agree that a daily dose of 300 milligrams or less is safe for most people, including pregnant women.
And as research continues, scientists may yet find more evidence to make our morning lattes seem as good for our bodies as they are for our brains.
“If you’re not drinking coffee or tea, don’t start because of the health benefits,” says Michele Tuttle, a registered dietitian in Columbia, Md. “But if you’re already drinking them, enjoy in moderation.”
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How much punch they pack
Healthful, unhealthful or somewhere in between, caffeine is likely safe at 300 milligrams or less per day. Here’s how it adds up in a variety of common drinks and pills.
*--* Product Serving size Caffeine NoDoz maximum strength 1 tablet 200 mg
Dexatrim diet pills 1 pill 200 mg
Excedrin 2 tablets 130 mg
Starbucks coffee short (8 oz) 130-327 mg*
SoBe No Fear 16 oz 158 mg
Regular brewed coffee 8 oz 135 mg
Energy shots 1 oz 100 mg
Instant coffee 8 oz 95 mg
Red Bull 8.5 oz 80 mg
Black tea 8 oz 40-70 mg
Java Water 8 oz 62 mg
Starbucks Coffee Ice cream 1 cup 40-60 mg
Starbucks latte short (8 oz) 58 mg
Mountain Dew and Diet Mountain Dew 12 oz 55 mg
Espresso 1 oz 30-50 mg
Dannon Coffee Yogurt 8 oz 45 mg
Green tea 8 oz 25-40 mg
Diet Coke 8 oz 34 mg
Hershey’s Special Dark Chocolate Bar 1 bar (1.5 oz) 31 mg
Pepsi 8 oz 28 mg
Diet Pepsi 8 oz 27 mg
Coca-Cola Classic 8 oz 26 mg
Snapple Iced Tea 8 oz 24 mg
Jolt gum 1 piece 20 mg
Energy mints (various brands) 1 mint 2-15 mg
Hershey’s Milk Chocolate Bar 1 bar (1.5 oz) 10 mg
Decaffeinated coffee 8 oz 5 mg
Chocolate milk 8 oz 5 mg
Hot cocoa 8 oz 5 mg
Decaffeinated black tea 8 oz 4 mg
*depends on brewing process.
Graphic reporting by Emily Sohn
CENTURIES OF CAFFEINE
Stone Age: People chew leaves, seeds, bark of certain plants to relieve fatigue.
2737 BC: Legend describes how Chinese Emperor Shen Nung’s servants are boiling water when leaves fall in, creating the first pot of tea.
600 BC: The earliest evidence of cocoa in an ancient Mayan pot dates to this time.
Circa 780: Chinese scholar Yu Lu writes first book on tea.
1000: People on the Arabian peninsula first cultivate coffee plants, then roast and boil the beans to make a beverage called qahwa.
1475: The first coffee shop opens in Constantinople.
1519: Aztec Emperor Montezuma presents Spanish explorers with a bitter chocolate drink.
1654: Soon after coffee enters Europe, Italy’s first coffee shop opens.
1700: Chocolate is now a popular beverage in Europe.
1773: To protest British taxes, colonists throw tea into the harbor during the Boston Tea Party, a prelude to the American Revolution.
1819: German chemist Friedrich Ferdinand Runge isolates the white crystalline chemical caffeine from Arabian mocha beans.
1822: The prototype of the first espresso machine is created in France.
1880s: The world’s first caffeinated soft drinks, including Coca-Cola, are created.
1908: The first drip coffeemaker is invented by German housewife Melitta Bentz.
1911: The U.S. government seizes 40 barrels and 20 kegs of Coca-Cola syrup in Chattanooga, Tenn., charging that the caffeine in it is dangerous. Coca-Cola wins.
1938: Nescafe instant coffee is invented.
1958: The Food and Drug Administration classifies caffeine as generally recognized as safe (GRAS).
1970s: Flavored coffees become popular in the U.S.
2001: More than 77% of adults drink coffee daily or occasionally (National Coffee Assn.).
2004: Caffeine is removed from the International Olympics Committee’s list of banned substances.
-- Emily Sohn