"If it weren't for the coffee," David Letterman once quipped, "I'd have no identifiable personality whatsoever."
That's a sentiment most coffee lovers can understand.
Treasured as it is, however, coffee has been blamed for a range of ills, from heart disease and cancer to osteoporosis. Are health dangers really lurking in our lattes?
Health experts offered reassuring words at the 1999 annual meeting of the American Dietetic Association: Drinking up to three cups of coffee a day poses no risk. What's more, coffee appears to have some surprising benefits.
It's easy to see why researchers take coffee seriously. One cup contains about 100 milligrams of caffeine -- enough to give infrequent coffee drinkers a potent kick, says Tony Chou, MD, a cardiologist at the University of California, San Francisco, and an authority on how coffee affects our health. Half an hour after a good strong cup, a coffee drinker's resting metabolic rate -- the number of calories burned just sitting quietly -- increases by as much as 10%. Blood pressure climbs. Heart rate accelerates. Breathing speeds up.
Researchers used to worry all that commotion was harming our hearts. But regular coffee drinkers quickly develop a tolerance to caffeine, Chou says. After a week or two, they don't get so much as a wobble in their blood pressure. Habitual coffee drinkers are no more likely to suffer from hypertension than people who never pour a cup.
Even patients with irregular heartbeats, or arrhythmia, don't seem to be troubled by caffeine, according to a study published in the Annals of Internal Medicine in January 1991. Toronto scientists reviewed five studies of people with arrhythmia. Drinking up to five cups of coffee a day, they found, didn't make anyone's heart more likely to skip a beat.
Nor does coffee appear to increase the risk of heart disease, according to a 10-year study of more than 85,000 women. In the February 1996 Journal of the American Medical Association, Harvard researchers reported that women who drank six or more cups of coffee weren't any more likely to have a heart attack than women who drank only one or two cups.
Plenty of other alarms have turned out to be false. A few years back, headlines warned about a possible link between coffee and breast cancer. But in the February 1998 European Journal of Cancer Prevention, Italian researchers reported finding no link. The other worry, concerning osteoporosis, didn't hold much water either. Results of a study published in the June 1997 American Journal of Clinical Nutrition showed that bone thinning wasn't more likely in women who drank coffee.
Jogging the Brain
The bottom line: Coffee seems to be harmless for most people. And studies suggest that a cup may actually offer some impressive benefits. In the August 1999 issue of Physiology and Behavior, for instance, English researchers reported that volunteers who drank caffeinated coffee in the morning performed better than nondrinkers on tests that involved learning new information. That holds true for the elderly as well, according to a study in the January 2002 issue of Psychological Science. And a study published in International Journal of Sports Medicine in August 1999 found that attention, psychomotor skills, and long-term memory all improved during the few hours after volunteers drank caffeinated beverages.
Why? Caffeine keeps us alert not by speeding us up but by keeping us from slowing down, according to Michael Bonnet, PhD, professor of neurology at Wright State University in Ohio. Each time brain cells fire, they produce a squirt of a chemical that serves as an "off" switch that keeps neural activity in check. Caffeine, in effect, blocks the chemical -- jamming the switch so that it can't be turned down.
Caffeine also may boost levels of brain-cell calcium, a mineral we know is important in memory. In experiments reported in the October 1999 issue of Proceedings of the National Academy of Sciences, an Israeli researcher observed a calcium increase in brain cells exposed to caffeine.
Is There Any Reason Not to Love Coffee?
However, too much caffeinated coffee can cause problems, experts say. Because caffeine is a stimulant, it can aggravate sleep problems like insomnia.
If you're having trouble getting pregnant, you might want to think about laying off coffee. A few studies have linked caffeine to infertility (although others have found no association).
Finally, if you're feeling anxious or depressed, it's worth easing up on the caffeine, which can exacerbate symptoms.
Originally published Nov. 29, 1999.
Updated Jan. 24, 2002.