CNN  — 

Ultramarathoners and other endurance runners take note: You can’t rely on electrolyte sports drinks and supplements to keep essential salt levels in balance and prevent illness during and after these grueling races, according to a new study.

Researchers from Stanford University evaluated 266 athletes who took part in RacingThePlanet – an extreme sporting event that involved running 155 miles over seven days across rough terrain in different deserts around the world. Dr. Grant Lipman, the lead author of the study, said the findings were applicable to other sports.

The study, which published Tuesday in the Clinical Journal of Sports Medicine, focused on 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.

Exercise-associated hyponatremia can lead to altered mental status, seizures, pulmonary edema and even death.

Their study showed that hot weather increased the rates of these types of illnesses, but use of sodium supplements did not prevent EAH.

“In the past, athletes were told to make sure they’re taking electrolyte supplements and drinking as much water as they can,” said Lipman, a professor of emergency medicine at Stanford and director of Stanford Wilderness Medicine.

“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.”

The 61 women and 205 men in the study ran in one of five different races held in 2017 and 2018 in South America, Namibia, Chile and Mongolia. Ninety-eight of the runners competed in temperatures that averaged over 93 degrees Fahrenheit (33 degree Celsius).

Some runners took salt tablets every hour, while others diluted electrolytes in a water bottle, Lipman said.

“There are multiple different methods. However, most electrolyte strategies end up with a drink that has a lower sodium concentration than what is found in the body. This is why drinking too much electrolyte solutions can result in EAH. “