"It's not just the amount of coffee or soda you drink each day, but how your body manages caffeine," said Dr. Kirk N. Garratt, an interventional cardiologist at Lenox Hill Hospital in New York City.
Garratt was not involved in the study, which was conducted by a Canadian team at the University of Toronto. The researchers published their findings in the March 8 issue of the Journal of the American Medical Association.
They looked at a gene for an enzyme called CYP1A2, responsible for the metabolism of caffeine in the liver. One form of the enzyme, produced by the gene variant 1A, metabolizes caffeine rapidly while another form, 1F, metabolizes it slowly.
The researchers performed gene tests on more than 4,000 residents of Costa Rica. Half had suffered nonfatal heart attacks while the other half had no history of heart problems, reports Forbes.
According to Houston Chronicle, 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.