For recreational athletes, too, the effects can be dramatic. A runner who is able to complete a 10K race in 40 minutes without caffeine could shave off 72 seconds with caffeine. And caffeine could allow a cyclist competing in a one-hour time trial to drop a minute and a half.
Ganio said it is important to take the right dose, which shakes out to about three to six milligrams per kilogram of body mass. That is a lot of caffeine. An 80-kilo (176-pound) athlete taking six milligrams per kilogram would need 480 milligrams of caffeine.
“That’s four strong cups of coffee,” said Ganio. “If you can tolerate it, it seems to be the upper end of what you can have to improve performance.”
Since “cups of coffee” is a notoriously imprecise measure of caffeine, it may help to think of it this way: 480 milligrams would be six 8-ounce Red Bulls, two and a half NoDoz tablets, or two Extra Strength 5-hour Energy shots. A more moderate dose for a smaller athlete, say, a 65-kilo (143-pound) athlete taking three milligrams per kilo, is still an impressive amount of caffeine: equal to one NoDoz tablet, one 5-hour Energy shot, or two and a half Red Bulls. Even this amount of caffeine is difficult to obtain using caffeinated sodas like Coca-Cola. A 65-kilo athlete would need to chug nearly six cans of Coke at once to get a caffeine dose of three milligrams per kilogram.
According to Ganio, endurance athletes have other misperceptions about caffeine. One of those is that it will dehydrate you.
One hydration study followed 59 healthy male volunteers for 11 days, using varying levels of caffeine. The researchers found no evidence of dehydration. “These findings question the widely accepted notion that caffeine consumption acts chronically as a diuretic,” the scientists concluded.
While this finding will seem counterintuitive to many coffee drinkers, especially commuters who have suffered through bladder-bursting traffic jams, Ganio said the science bears it out. Twelve ounces of coffee or 12 ounces of water will have about the same effect.
Evan Johnson, Ganio’s research colleague, explains that because individual reactions to the drug vary widely, caffeine is not for every athlete and best used judiciously.
“I have a little bit more of a public health overview of our use of caffeine in our nation,” he said. “You find a lot of people who constantly ingest caffeine throughout the day, and therefore at bedtime have trouble going to sleep; and then need alcohol or some sort of sleep aid to get to bed, and then in the morning are so groggy that they need caffeine again to get back into this kind of vicious cycle of supplementation. And I think when you get to that stage, it’s definitely a negative standpoint.”
While some athletic organizations such as the National Collegiate Athletic Association (NCAA), still limit caffeine—as they do other performance-enhancing substances—most now do not. Until 2004, the World Anti-Doping Agency and the International Olympic Committee considered 12 micrograms per milliliter in urine to be the maximum legal concentration. But they dropped caffeine from their list of prohibited substances in 2004 because caffeine is so ubiquitous that setting a threshold might lead athletes to be penalized for what others would consider normal caffeine consumption.