Coffee and the heart

Coffee, heart

Like those irritating tunes you just can't get out of your head, some medical "facts" stay with us even when they turn out to be false. Take the connection between coffee and heart disease. Many people think that drinking coffee harms the heart. Not so. It may pose problems for people who over-caffeinate themselves or who are extra-sensitive to caffeine. But for most people, drinking coffee is a harmless habit.

​If coffee did tinker with the ticker, we'd be in big trouble. Almost 110 million Americans drink coffee every day, about 9 billion gallons of the bitter brew a year. That's enough to fill the Empire State Building every other week.

​Suspicion about coffee's effects on health has dogged its reputation for centuries. In 1679, French physicians claimed that coffee drinking led to exhaustion, paralysis, and impotence. At the beginning of the 20th century, some medical textbooks equated coffee "addiction" with morphine abuse and alcoholism. Studies in the middle of the 20th century linked coffee drinking with pancreatic cancer, high blood pressure, and heart disease. But this early research often failed to take into account cigarette smoking, once a habit of many coffee drinkers, that was the real link to health problems.

​Coffee isn't totally innocuous. Its main active ingredient, caffeine, is an addictive, mood-altering substance. But drinking a few cups of coffee a day barely registers on the scale of heart risks. Drinking tea, which delivers half the caffeine of coffee, is even safer, and just might protect the heart. (Watch for an article about tea's effects in an upcoming Harvard Heart Letter .)

​Cardiovascular Effects

Hundreds of compounds give brewed coffee its unique aroma and taste. Caffeine has received almost all the attention, though others are coming under closer scrutiny.

​The caffeine in a cup of coffee slightly speeds the heart rate in some people. It also constricts the peripheral arteries (those in the brain, arms, legs, and other regions away from the heart and lungs). This is one reason why a cup of coffee can sometimes ease the throbbing pain of a headache caused by swollen blood vessels in the brain. Its other effects, or noneffects, on the cardiovascular system include:

  • Blood pressure: A cup of coffee temporarily boosts blood pressure in nondrinkers, but not in people who drink it regularly. Can this short-lived effect lead to high blood pressure among regular users of the bean?

According to the latest national guidelines on blood pressure, most studies have shown no clear connection between caffeine intake and high blood pressure. The latest report on the subject concurs. Among nearly all the 1,000-plus men who graduated from Johns Hopkins School of Medicine between 1947 and 1968, systolic and diastolic blood pressures were marginally higher in those who quaffed five or more cups a day (122.2/76.7 mm Hg) than they were in people who didn't drink coffee (121.3/75.4 mm Hg). But after taking into account factors known to elevate blood pressure, such as cigarette smoking, alcohol drinking, weight, and exercise, researchers found coffee drinking had little impact on the development of chronic high blood pressure. (Archives of Internal Medicine 2002, Vol. 162, No. 6, pp. 657-62.)

  • Cholesterol: Two substances in brewed coffee--kahweol and cafestol -- increase cholesterol levels. Since paper filters trap these compounds, they're absent from most American coffee and pose a problem only for those who drink espresso or other types of unfiltered coffee. Even then, the effect is modest. Drinking six cups of unfiltered coffee a day increases cholesterol about 12 mg/dL.
  • Homocysteine: Last year, two very different studies showed a connection between coffee consumption and homocysteine, a substance found in the bloodstream that may increase the risk for heart disease (Harvard Heart Letter, March 2002). In a trial that included 191 coffee drinkers, homocysteine levels fell among those who quit cold turkey for six weeks. In the other study, a survey of more than 3,000 Dutch men and women, homocysteine levels were slightly higher in those who drank six or more cups a day compared with those who didn't drink coffee.
  • Heart rhythms: In some people, drinking coffee leads to the occasional missed or extra heartbeat or a speedup in the heart's rhythm. For most people, including those with heart disease, coffee doesn't disturb the heart's rhythm. If you feel that caffeine affects your heartbeat, slowly cut back on the amount you drink each day-- or mix regular and decaffeinated coffee--and see what happens. (If you drink alcohol, cutting that back may also offer relief, since alcohol is more likely to interfere with the heart's rhythm than caffeine.)
  • Heart disease: Long-term studies of very different populations have shown little association between coffee drinking and heart disease. In two of the largest--Harvard-based studies of female nurses and male health professionals --there was no increased risk for heart disease even among those who drank up to five cups of coffee a day.

Coffee Consensus

The American Heart Association and American Medical Association agree that drinking a few cups of coffee a day won't harm most people.

​Two Harvard doctors offered an excellent bottom line about coffee drinking in a 1998 editorial in the American Heart Journal. After first acknowledging that some people are more sensitive to caffeine than others and may feel that it affects their hearts, Thomas Graboys, M.D., and Susanna Bedell, M.D., suggest that "common sense once again dictates that if coffee bothers you, don't drink it; otherwise why should we physicians, as we all too often do, modify life's pleasures without a sound basis of scientific accuracy to do so?"

​from Harvard Heart Letter, Harvard Health Publications