TUESDAY, March 7, 2006 (HealthDay News) -- Genes may determine whether or not caffeine raises a coffee lover's risk for heart attack, a new study finds.
"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.
It turned out that the two forms of the gene were present almost equally in each group -- 55 percent of those who had had a heart attack and 54 percent of the problem-free group carried the slow-metabolism version.
Scientists have known for some time that the CYP1A2 gene exists in two forms, said Ahmed El-Sohemy, who holds a research chair in nutrigenomics at the University of Toronto and led the study. The belief was that the slow-metabolizing form could affect the heart because it makes caffeine linger in the body. "That is exactly what we found," he said. "The effects were quite striking."
Differences emerged when the researchers used a food questionnaire to track caffeine intake. Carriers of the slow-metabolism form of the gene who drank 2 to 3 cups of coffee a day had a 36 percent higher risk of heart attack than those with the faster form of the gene. For those who drank four or more cups a day, the risk was 64 percent greater.
Younger people in the slow metabolism group had an increased risk. The risk for those under 59 who drank four or more cups of coffee daily was double that of those who drank less than a cup a day, and it climbed to four-fold higher for those under 50.
The age effect could be due to the fact that older people tend to have more risk factors for heart attack, anyway. That risk might overshadow any caffeine effect, El-Sohemy said.
The study explains why definite links between caffeine and heart attacks have been tough to pin down, Garratt said.
"If you go through the literature you find a lot of papers suggesting that caffeine is entirely harmless and others suggesting an increased risk of heart attack," he said.
Garratt noted that coffee isn't the only caffeine source out there -- many popular soft drinks also contain caffeine.
The study "underscores the importance of assessing individual patients to determine who should cut back and who can continue to use caffeinated products without restriction," he said.
The time when such assessments move into medical practice might not be far away, he added.
"We are quickly moving into a time when genetic testing of this type will become standard," he said. "There will be a chip that you give a drop of blood and get information about 20 or 30 different characteristics. If caffeine turns out to be as important as the study suggests, that might be included in the test."
But even people who are found to carry the riskier, slow-metabolizing version of the gene can take some comfort from the study results, Garratt said.
"It shows that if your consumption is modest, one or two cups a day, your risk remains low even if you're a slow metabolizer, he said."
Find out more about caffeine at the American Heart Association.