People who drink four or more cups of coffee a day increase their risk of a heart attack by 40% and those at high risk for heart attacks should consider limiting their consumption, researchers at the Kaiser Permanente Medical Center in Oakland advise in a new study.
But the study, which is the latest contribution to a decades-long debate over the possible link between cardiovascular disease and coffee, was immediately assailed by critics and undoubtedly will leave coffee-lovers in a quandary about health effects of the brew.
"This beverage is consumed by most adults in this country. And despite studies back and forth, you can't nail coffee with anything," said Dr. Harvey Wolinsky, a cardiologist at Mount Sinai Hospital and Medical Center in New York. Wolinsky, who is not affiliated with the National Coffee Assn., reviewed the study at the request of the association.
The study, published in the September issue of the American Journal of Epidemiology, also marks a reversal for this Kaiser research group. In 1973, the researchers reported in the Journal of the American Medical Assn. that scientific findings failed to find a connection between coffee consumption and heart attack. A number of other studies that have also found no link.
"If you want to get people down on you and hollering at you, write something about coffee," said Dr. Arthur Klatsky, who published the study with co-investigator Gary Freidman.
The new study was based on 101,774 individuals undergoing routine medical care at Kaiser Permanente hospitals in Northern California from 1978 through 1985. Thirteen percent of those studied said they drank four to six cups a day and about 4.5% said they drank more than six cups. Researchers attempted to control contributing heart disease factors such as smoking, obesity and age--in order to highlight the effects of coffee.
Klatsky said he cannot explain why the new study showed an increased risk for heart attack when other studies, including their own, have not. But he said he does not rule out the possibility that a factor other than coffee consumption might have caused the increased risk for heart attack.
For example, while the Kaiser study revealed an increased risk for people consuming four to six cups a day, it failed to show a greater increase in risk among individuals consuming more than six cups of coffee a day, which would be expected, he said.
Moreover, the research did not find an increased risk of heart attack among people who drink four or more cups of tea, which also contains caffeine but usually in smaller amounts. But Klatsky said researchers still suspect that caffeine is the culprit in heart-attack risk and that tea drinkers are not simply consuming as much caffeine as coffee drinkers, he said.
The study did not attempt to distinguish between drinkers of caffeinated coffee and decaffeinated coffee.
Despite these factors, it is still prudent for people at high risk for heart disease to limit coffee consumption, Klatsky said.
"We still do not advise withdrawal of the solace of a cup or two, but our new study is consistent with the view that heavier coffee use increases myocardial infarction risk," the researchers concluded in their paper. "We now suggest that persons at high risk of myocardial infarction should limit coffee use to less than four cups a day."
But, Klatsky said: "I think there should be more studies and that they should examine the lifetime history of coffee use, the type of coffee--caffeinated or decaffeinated--and brewing methods."
Klatsky said the Kaiser group decided to re-examine their 1973 study after several researchers published reports in the 1980s showing an increased risk of heart disease among heavy coffee drinkers. In the 1970s, the coffee-heart disease connection had been dismissed by most scientists.
But, he said, "We didn't expect to have to reverse ourselves. But we thought the first study was probably correct."
The Kaiser 1973 study probably was correct, said Wolinsky.
He said the number of heavy coffee drinkers in the Kaiser study who had heart attacks was too small for an accurate assessment of risk.
Wolinsky also said he suspected that the heavy coffee drinkers might have under-reported their smoking habits. Smoking is known to increase the risk of heart attack.
Further, the Framingham Study on heart disease, one of the largest on heart disease risk factors, has failed to find an association between coffee and elevated risks, he said.
"The important thing is that the Framingham study cannot find a whit of a relationship between coffee consumption and any cardiovascular disease parameter (such as high blood pressure or elevated cholesterol levels)."
Wolinsky said people should avoid excessive consumption of any product but should not worry in particular about the risks of drinking coffee.
In a statement, the National Coffee Assn. also cited the Framingham study as the most conclusive assessment of heart-attack risks.