Here's a real caffeine jolt — heart
attacks might be a risk for coffee drinkers with a common
genetic trait that makes caffeine linger in their bodies,
a study suggests.
Research on more than 4,000 people in Costa Rica found
that about half had the trait and were considered "slow
caffeine metabolizers." The other half had the opposite
trait, which caused their bodies to rapidly break down
or metabolize caffeine, and coffee-drinking in this group
appeared to reduce heart attack risks.
Among slow-metabolizers, those who drank two or more
cups of coffee daily were at least 36 percent more likely
to have a nonfatal heart attack than those who drank little
or no coffee. Even higher risks were found for younger
slow metabolizers — those under 50. They were up
to four times more likely to have a heart attack than
slow metabolizers in their age group who drank little
or no coffee.
The findings, though preliminary, might explain why there
have been such mixed results in previous studies investigating
caffeine's effects on the cardiovascular system, said
University of Toronto researcher Ahmed El-Sohemy, a study
co-author.
Caffeine is thought to block the effects of a certain
chemical that is believed to help protect against tissue
damage, he said.
Some previous research has linked coffee-drinking to
a higher risk of heart disease, but other studies have
suggested the opposite. While there's evidence to suggest
caffeine can cause short-term blood pressure increases,
a study last year said coffee-drinking didn't appear to
cause long-term high blood pressure, at least in women.
The new study "clearly illustrates that one size does
not fit all," El-Sohemy said. "Perhaps in the future we'll
be making different (dietary) recommendations based on
people's genetic makeup."
For now, there's no easy way to know if you're a fast
or slow caffeine metabolizer. Staying awake all night
if you drink coffee in the afternoon doesn't mean you're
a slow metabolizer, and a genetic test that could answer
the question is used in research but is not commercially
available, El-Sohemy said.
His study, conducted with researchers from Harvard's
School of Public Health and the University of Costa Rica,
appears in the Journal of the American
Medical Association.
Participants were 2,014 men and women aged 58 on average
who'd had a nonfatal heart attack between 1994 and 2004,
plus a control group of 2,014 healthy men and women. Genetic
tests of blood samples determined which ones were slow
caffeine metabolizers and which were fast metabolizers.
El-Sohemy said the prevalence of both traits is similar
in other population groups but that worldwide prevalence
varies.
"This data is very provocative and very interesting,"
said Dr. Roger Blumenthal, a cardiologist at Johns Hopkins
Medical School who was not involved in the study.
Still, even if future research confirms the findings,
it's likely that caffeine plays a much smaller role in
heart attacks than conventional risk factors like high
blood pressure, cholesterol and smoking, Blumenthal said.
Dr. Nieca Goldberg, an American
Heart Association spokeswoman, said that while
the results aren't conclusive, "One good message that
we can give people is that life is about moderation."
The study "doesn't say you can't have caffeine," but
drinking several cups of coffee daily is probably excessive
for some people, she said.
Coffee can trigger heart palpitations in people who are
sensitive to caffeine. Those palpitations may not be harmful
but they can be frightening, Goldberg said. She noted
that caffeine is found in other foods including colas
and chocolate.
