Hydration Guide for Runners (And How to Not Overdo It)

Marathon Runner Hydration
Photo: Pond5

It’s getting hot out there and for many long-distance runners, that means thinking about proper hydration. For years, most runners have put laser focus into preventing dehydration, fearing its effect on performance and health. And for good reason: Up to 75 percent of Americans may be functioning in a chronic state of dehydration, (drinking less than the recommended 64 ounces per day). Less recognized, however, is that it’s not necessarily dehydration that could get you, but rather overhydration, or hyponatremia. While less than 200,000 Americans in the general population are impacted by it at any given time, in an endurance event, it can be one of the top two conditions to present in the medical tents.

In simple terms, hyponatremia is reduced blood sodium concentration. Left unchecked, the condition can lead to vomiting, confusion, seizures and worse. That’s where knowing the hydration rules for your body come into play. With a little understanding and practice, you can make sure you stay in the safety zone between too little and too much fluid intake.

Hyponatremia Explained

It’s dismissing that inherent ability to “drink to thirst” that has gotten many runners in trouble in the age of modern racing, Cucuzzella says.

Pretty much all runners know what dehydration is and work hard to prevent it, yet most don’t realize that a little bit of dehydration is actually OK. “Most runners will safely lose two percent to four percent of their weight during a two hour event as water is attached to glycogen, which you burn for fuel,” explains Mark Cucuzzella, MD, elite marathoner and director of the Freedom’s Run series of races. “Your body is pretty well designed to run an endurance event — you just need to tap into your senses.”

It’s dismissing that inherent ability to “drink to thirst” that has gotten many runners in trouble in the age of modern racing, Cucuzzella says. He subscribes to the research carried out by Dr. Timothy Noakes, a South African professor of exercise and sports science and author of the book Waterlogged. Both argue that the sports drink industry has done a number on runners’ natural thirst gauge, causing them to override the thirst signal and drink too much. 

Luckily, race organizations are becoming more aware of conditions like hyponatremia and have medical tents that are set to handle it when presented, says Matthew Sedgley, MD, a sports medicine physician based in Westminster, MD, who has also served as medical director for multiple marathons. “Typically these races have a sports medicine physicians’ meeting a few weeks prior to the race and review the latest research,” he says. “The organizations annually update topics such as hyperthermia, hypothermia and hyponatremia.”

Indeed, the Rock ‘n’ Roll Marathon series, one of the nation’s largest such organizations, has a full paper out on hyponatremia that it shares on its website to educate runners. PZ Pearce, MD, medical director for the series, says that hyponatremia is one of the two main conditions the organization sees in its medical tents, the other being heat stroke. “There are three main factors that contribute to the condition,” he says. “Exercise, taking in too much fluid at the aid stations, and the fact that runners sweat salt and lower the sodium content in their blood. It’s the perfect storm leading to a slow dilution of sodium levels.” 

Getting It Right

As a runner, it’s important to know the signs of hyponatremia as well as how to prevent it. “Early symptoms include weight gain, puffiness, nausea, headache, and a general feeling of being ‘off,’” says Cucuzzella. “More serious symptoms can include vomiting, confusion, irritability and seizures. Keep an eye out for these symptoms even a few hours after the race. If you are not sweating heavily and/or feel you may have gained weight, don’t drink large amounts of fluids until you are urinating normally.” 

When runners arrive at the med tent with symptoms of hyponatremia, the organizers should first test for sodium levels before giving any IV fluids because doing so could cause immediate harm, Cucuzzella says. To ensure athletes remain safe during his marathon, Cucuzzella circulates hydration guidelines the week prior to the event and only places aid stations every three miles on the course. 

For runners, all three physicians recommend drinking to thirst only. “There’s a misconception that if you are not drinking water but drinking an electrolyte fluid instead that you cannot get hyponatremia, but that isn’t true,” Sedgley points out.

Hydration How-To

To maintain the optimal hydration balance, the American Road Race Medical Society has adopted guidelines from which runners can develop their own plan. Here are some quick tips to hold your own:  

Avoid playing copycat. Each runner has unique hydration needs, so be wary of following other runners’ leads just because they appear to know what they’re doing. The same goes for generalized “rules” you might hear about frequency and amounts. Learn what your body requires by fine-tuning your hydration plan during your training runs.

Weigh it out. Knowing your sweat rate can be a good indication of how much to drink. To calculate it, weigh yourself without clothes before and after a long training run to gauge how much you typically lose through sweat. While your goal isn’t to match your sweat rate in fluid consumption, you should try to get as close to it as is comfortable, and be careful not to exceed it.

Choose wisely. When training or racing for more than two hours, especially if you have high sweat loss, reach for fluids with sodium, such as a sports drink. When training for shorter durations, plain water is adequate.

Do not over drink. “We usually find that athletes who develop [hyponatremia] drink over one cup every 20 minutes,” Pearce writes. “If a participant stops at every fluid station and drinks just one cup (eight ounces) sports drink or water, they will be hyponatremic by mile 17.” Trust your thirst, and during training runs, use your pre- and post-run weight as  your guide. Weight gain is a sure sign you’re drinking too much.  

Know your colors. Aim for your urine to be a pale yellow hue, rather than dark like apple juice (a sign of dehydration) or clear like water (which might signal overhydration).

Act fast. If you are not feeling well during or after the race and simple changes don’t make you better, don’t try to tough it out. It’s always best to seek medical help right away, so that you don’t progress into dangerous territory.

Cucuzzella recommends that you practice your hydration plan well before race day, and learn to trust it. “If something is not going well, figure out why versus simply reacting,” he says. “Too often, its this reaction that gets runners in trouble. They start crashing, slowing down and overdrinking. My strategy is simple: Drink when you are thirsty.”

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