Running in the Summer? Follow These Tips to Avoid Dehydration

Whether you’re racing in a marathon or jogging around the block, Tufts exercise scientist Roger Fielding has advice to keep you healthy

Running season is here, and athletes of all levels need to watch their water intake. Dehydration, a risk that increases in warmer weather, can reduce mental activity and physical coordination, as well as contribute to fatigue, urinary tract infections, kidney stones, cardiovascular stress, and more, said Roger Fielding, director of the Nutrition, Exercise Physiology, and Sarcopenia Laboratory at the Jean Mayer USA Human Nutrition Research Center on Aging at Tufts, and professor at the Friedman School of Nutrition Science and Policy.

“People should be thinking about hydration before they start to lose too much fluid from sweating,” Fielding said. “When people begin to sense they’re getting thirsty, it’s almost too late to start trying to recover some of those fluid losses.”

Here are some of Fielding’s hydration best practices to follow.

Know how much water you need.

“People should be thinking about hydration before they start to lose too much fluid from sweating,” Roger Fielding said.“People should be thinking about hydration before they start to lose too much fluid from sweating,” Roger Fielding said.
According to the National Academy of Science, 15.5 cups of water per day is adequate for most men and 11.5 cups for most women (more if they are pregnant or lactating). This can be used as a baseline, although it will vary based on body size, altitude, and more.

Weigh your options. For athletes, it’s also important to establish how much more water you need to drink in hot weather. A simple way to do this is to weigh yourself before and after the activity. “Any weight loss is going to be largely evaporative sweat loss,” Fielding said, “which you need to account for by replacing the amount of fluid you lose.”

Track your fluid intake. Fill a container in the morning with the amount of water you need to drink in a day, and then finish it before the end of the day. The color of your urine can also be a clue to hydration status. If it is deep yellow, it could indicate you are not drinking enough.

Build new habits. Make it routine to drink water before a meal, before you get out of bed in the morning, or whenever you start a new activity. Carry a water bottle when you go out and keep a quart container in view at work—whatever reminds you to hydrate early and often.

Watch the weather. Heat can present one challenge, but humidity creates another. “The main reason we sweat is to dissipate heat,” Fielding said. “Environmental temperature is important, but also if it is a very humid day, your capacity to evaporate sweat and dissipate heat is reduced.” Consider shifting your running schedule away from when humidity is at its worst.

Eat a water-dense diet. To up your fluid intake, incorporate soups and stews into your regular diet, along with water-dense fruits and vegetables such as melons, grapes, oranges, cucumbers, celery, tomatoes, and peppers.

Limit sugar-sweetened beverages. “Sugar does facilitate some absorption of fluid by your small intestine and help you rehydrate more quickly,” Fielding said. “But if someone is just recreationally active, there is no real benefit.” Most people should avoid sugary drinks, as well as sweetened drinks with added electrolytes—options such as Gatorade are not necessary for lighter exercise, because you don’t lose enough electrolytes through sweat to need to replenish them.

Hydrate even if you’re not thirsty. The brain triggers thirst in response to low fluid balance in the body. But don’t use thirst as your sole measure of when to drink. Some people feel or notice thirst less than others, particularly aging individuals—this can be a problem, because the loss of as little as two to three percent of body fluid can cause physical and cognitive impairment in some people.

Over-hydrating isn’t usually a concern. Although drinking too much water, especially right before exercise, can cause gastrointestinal distress—and excessive fluid intakes can cause other problems—most people don’t have to worry. “We regulate our fluid pretty well,” Fielding said. “The concern is mostly on the other end—the groups of people who don’t consume enough.”

Monica Jimenez can be reached at

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