Coffee-heart attack link a wake-up call

At least, that is the finding of a study conducted by Dr. Ana Baylin, assistant professor of community health at Brown University. She, with help from her colleagues at the Harvard School of Public Health, studied the coffee-drinking habits of 503 Costa Ricans who had experienced a nonfatal heart attack between 1994 and 1998.

"We found that light and moderate coffee drinkers did have heart attacks" in the hour following their first or second cup of coffee, Baylin said. "Most of them were regular drinkers of one cup a day."

But heavy drinkers - of four or more cups a day - seemed less susceptible to the short-term effects, she said, and did not experience a heart attack within the hour following coffee consumption. Therefore, the researchers determined, coffee might not be a trigger for them. "Tolerance to caffeine is developed very quickly," Baylin said of possible reasons heavy drinkers were less susceptible to the short-term effects of coffee drinking. "This is a hypothesis, of course ... but it makes sense."

Baylin said moderate coffee drinkers, by having two or three cups a day, increased their chance of having a heart attack by 60 percent. And light coffee drinkers, who drink one cup or less daily, increased their risk by more than four times.

One possible reason: The caffeine in coffee increases sympathetic tone, a component of the central nervous system that affects heart rate and blood pressure, she said. For those already at risk of heart attack - because of smoking, high blood pressure, high cholesterol, obesity and diabetes - increasing sympathetic tone, which increases heart rate and blood pressure, could rupture the plaque on artery walls, causing a heart attack, Baylin said.

"All of them had risk factors," she said of the 503 adults in the study. "Some had more than others."

But the study is not without its critics. Robert Eckel, professor of medicine at the University of Colorado and former president of the American Heart Association, said he has reservations about the study's suggestion that coffee is a trigger of non-fatal heart attacks. "All of the coffee data are highly conflicting," Eckel said. "[Baylin's study] doesn't influence the bulk of literature that demonstrates no relationship between coffee and outcomes." Baylin said her study focuses on the acute, or short-term, effects of coffee in relation to heart attacks. That is what separates her study from others; most look at the chronic, or long-term, effect of coffee and its relation to heart attacks over time. "Some studies saw there was an effect," she said. "Some saw there wasn't."

Baylin noted the limitations of her study in an article this month in the peer-reviewed journal Epidemiology.

The fact that heart attacks are more likely to occur in the morning - when heart rate and blood pressure are naturally higher - is one limitation noted in the study, she said. It means the coffee-heart attack link might be coincidental.

Eckel said the small size of the sample population is another limitation, because "small studies always demand a larger sample size for power and validation." And, in order to prove the results of the study, she said, it would have to be replicated in other populations. Baylin said she is not planning to test the hypothesis in other populations.

However, she is planning to explore the relationship between genes, coffee, and heart attacks; she would use the same population. "One variant of DNA can separate the population into slow metabolizers and fast metabolizers of caffeine," which could be another factor in the coffee-heart attack link, she said.

Baylin added, "I would like to replicate [the future study] in another population, but that would be long-term."

www.pbn.com