Every day, millions of Americans rely on coffee to make it through the day. But what are its negative effects on the human body? The issue of whether or not it causes heart disease, for instance, has been a real point of contention in the medical community for years. The World Health Organization once suggested that coffee may be carcinogenic before backing away. So why are the effects of coffee—both positive and negative—so contested?
According to a report from The New York Times, it may come down to our genes. Dr. Ahmed El-Sohemy, a professor at the University of Toronto, noticed how coffee affects people differently, and he decided to find out why. The Times writes that it was a decade ago that he focused his attention on a particular gene that controls how quickly our bodies break down caffeine.
After conducting tests on groups of coffee drinkers who were separated by the rate in which they metabolize caffeine, Dr. El-Sohemy found that the slow metabolizers—those who had the slow variant of the gene—were likelier to suffer heart attacks.
“The increased risk that we saw among the entire population was driven entirely by the people that were slow metabolizers,” Dr. El-Sohemy said at the time. “When you look at the fast metabolizers, there was absolutely no increased risk.” In fact, Dr. El Sohemy found that fast metabolizers actually benefit from caffeine’s antioxidant properties.
But before you run off to have yourself tested for this gene—which was identified as CYP1A2—other researchers maintain that a number of different genes are involved in the metabolism of caffeine.
“There are clearly other genetic and environmental factors contributing to differences in caffeine metabolism,” said Dr. Marilyn Cornelis, an assistant professor at Northwestern University’s Feinberg School of Medicine, “and these are not captured by existing tests.”
If you’re curious about your own genes and whether or not you’re prone to fast or slow metabolism of caffeine, there are specific DNA test kits like FitnessGenes ($229) that can give you that information, just in case you wondering if that extra shot of espresso is one too many.