Electrolyte supplements popular with endurance runners can’t be relied on to keep essential sodium levels in balance, according to researchers at the Stanford University School of Medicine and their collaborators.

Rather, longer training distances, lower body mass and avoidance of overhydration were shown to be more important factors in preventing illness caused by electrolyte imbalances, the researchers found. Their study also showed that hot weather increased the rates of these types of illnesses.

“Electrolyte supplements are promoted as preventing nausea and cramping caused by low salt levels, but this is a false paradigm,” said Grant Lipman, MD, professor of emergency medicine at Stanford and director of Stanford Wilderness Medicine. “They’ve never been shown to prevent illness or even improve performance — and if diluted with too much water can be dangerous.”

Lipman is the lead author of the study, which was published online Feb. 25 in the Clinical Journal of Sport Medicine. Brian Krabak, MD, a sports and rehabilitation medicine specialist at the University of Washington-Seattle, is the senior author.

Providing care for ultramarathoners

Lipman and several of his co-authors are experienced at providing medical care for ultramarathoners and compete in ultramarathons themselves, so they are familiar with the challenges the athletes face. Ultramarathons are any foot race longer than a marathon. The idea for this study grew out of seeing firsthand how often endurance athletes use electrolyte supplements — whether taken in pill, powder or liquid form — and wanting to know if they prevented illness.

“In the past, athletes were told to make sure they’re taking electrolyte supplements and drinking as much water as they can,” Lipman said. “It was generally thought that that would prevent things like muscle cramping, electrolyte imbalances and dizziness. But there is currently no evidence to show this is true.”

Sodium levels that are too high or too low during exercise can harm athletes. This study focused on two conditions: hypernatremia, which occurs when sodium levels are too high and is associated with dehydration, and exercise-associated hyponatremia, or EAH, which is caused by a drop in sodium levels. EAH can lead to altered mental status, seizures, pulmonary edema and even death. There have been 14 such documented fatalities since 1985, according to previous studies.

“Most athletes worry about dehydration, but that won’t kill you,” Lipman said. “There have been multiple deaths from EAH, not only among endurance athletes but among military, football players and half-marathoners, as well.”

‘The perfect outdoor lab’

To conduct the study, researchers recruited 266 ultramarathoners from RacingThePlanet’s weeklong athletic events, which involve running 155 miles over seven days across rough terrain in extreme weather conditions at different deserts around the world.

“It’s the perfect outdoor lab for easily generalizable results,” said Lipman, who is on the medical advisory board and is research director for the events. Each of the study participants ran in one of five different races held in 2017 and 2018 in South America, Namibia and Mongolia. Data was collected on the fifth day of the event, when the athletes ran 50 miles. Ninety-eight of the runners competed in temperatures that averaged over 93 F.

“It’s a bit crazy,” said co-author Patrick Burns, MD, assistant professor of emergency medicine at Stanford and a participant in the trial, who completed one of the colder races — held in the Patagonia region of Chile. “The race started at 8 a.m. and I finished at 8 p.m. We ran trails through the woods with thousand-foot climbs and multiple river crossings up to your waist. It was cold and overcast and raining. I was soaked. My Achilles tendons were on fire.”