Sure, there are some top athletes who swear by the benefits of coffee. (Just ask New York City Marathon winner Shalane Flanagan, who has said: “Personally, I wouldn’t go to the line without a cup of coffee.”) And previous research has suggested that caffeine can improve performance, particularly in endurance sports. But now a new study shows that caffeine will not give everyone’s workout a jolt, and, in fact, it may even slow some people down, depending on the genetic hand they were dealt.
Experts have known for quite a while now that a particular gene is responsible for how quickly our bodies metabolize (or break down) caffeine, according to the New York Times. (The gene is officially known as CYP1A2, but we are affectionately calling it the caffeine gene.) About half of us have a variant of the caffeine gene that makes us fast metabolizers, while 40 percent have a variant that makes us moderate metabolizers. The remaining 10 percent are slow metabolizers, meaning the caffeine hangs around in their bodies the longest.
To find out whether there is a link between how quickly we process caffeine and the stimulant’s affect on athletic performance, researchers at University of Toronto recruited 101 male athletes and swabbed their cheeks for the caffeine gene. Over the course of three sessions, the men then rode their hardest for 10 kilometers on a stationary bike. Before pedaling, they were either given a placebo, a low dose of caffeine (two milligrams per kilogram of body weight) or a higher dose of caffeine (four milligrams per kilogram of body weight). “If you weigh 150 pounds (68 kilograms), that corresponds to either 136 or 272 milligrams of caffeine,” explained writer Alex Hutchinson on Outside. In coffee terms, a short dark roast from Starbucks contains 130 milligrams of caffeine.
When researchers looked at the results, caffeine boosted performance overall, with athletes on the higher dose of caffeine pedaling 3 percent faster than the placebo group — on average. But when researchers factored in the genetic component, the results shifted.
Athletes who were fast metabolizers pedaled 5 percent faster on the low-caffeine dose and nearly 7 percent faster on the high-caffeine dose. For moderate metabolizers, the caffeine was basically a wash, with times on the placebo and both high and low doses remaining the same. As for slow metabolizers? A high dose of caffeine seriously stalled their performance, slowing them down by 14 percent as compared to the placebo. Yikes!
While it is not yet clear how exactly caffeine and the caffeine gene alter athletic performance, study author Ahmed El-Sohemy, Ph.D., told the New York Times that the stimulant may give slow metabolizers an initial burst of energy, but then it likely lingers in their system, narrowing blood vessels and restricting the flow of blood and oxygen to worn-out muscles.
As for fast metabolizers, El-Sohemy explained that caffeine probably provides that same initial rush, but it is cleared from the body “before it could do the bad stuff.”
So how do you know if you are one of the lucky fast metabolizers or part of the 10 percent who will be slowed down by a coffee before the big race? You could track down a DNA test that would tell you which variant of the caffeine gene you have. Or you could simply trust your own experience: If a double cappuccino helps rev you up before a long workout, there is no need to give it up.