When Amby Burfoot won the 1968 Boston Marathon he didn't drink a single drop of water or anything else during the race. This wasn't unusual in those days. Runners generally avoided drinking during races and in training runs because they believed indulging their thirst would make them "waterlogged" and slow them down.
We now know that drinking during prolonged running enhances performance. For example, a study by English researchers found that men and women were able to run for 1 hour and 43 minutes at a moderate intensity when supplied with water compared to only 1 hour and 17 minutes when denied water.
The farther you run, the more important it is to drink. Although Burfoot and many of his contemporaries proved you can finish a marathon without drinking anything, you will almost certainly finish faster if you make an effort to limit dehydration.
But how much should you drink? And is water sufficient or is a sports drink better?
Listen to Your Thirst
The answer to the first of these questions has evolved. As recently as the early 2000s, many experts advised runners to drink as much as possible during marathons. This recommendation was based on the belief that any amount of dehydration diminished performance and increased the risk of overheating. But recent science has discredited these beliefs.
A number of studies conducted within the past several years have shown that runners perform no worse and become no hotter when they drink according to thirst—which typically replaces only 60 to 70 percent of sweat loss—than when they drink enough to replace 100 percent of sweat losses. What's more, the risk of gastrointestinal distress is significantly greater when runners drink as much as possible.
Based on these findings, the International Marathon Medical Directors Association now recommends runners drink according to their thirst during marathons. In other words, if you feel thirsty when you reach an aid station along the course, take a cup or two from a volunteer and drink. If you don't feel thirsty, pass the aid station and wait for the next one.
There's some nuance to this advice, however. Some runners are more mindful of their thirst than others. Those who aren't tuned in to their thirst are prone to drink less than they should. Pay close attention to your thirst when running a marathon and respond to it quickly. Don't allow your thirst to build for a long time before you take your next drink.
Listen to Your Stomach
It's also important to consider stomach comfort. As a general rule, if you drink as much fluid as you're thirsty for and no more, you will avoid gastrointestinal issues. But you may be able to drink a little more than the bare minimum required to keep your thirst at bay without triggering GI distress.
You're likely to perform better if you take advantage of this latitude. So when you approach each aid station in a marathon, tune in to your stomach as well as your thirst. If you're thirsty and you have a gut feeling (literally) you could drink a couple of good gulps instead of just one, go ahead and do that.