Data was collected from athletes at the beginning and end of the 50-mile race, when the exhausted, thirsty participants finally crossed the finish line. Prior to the race, the participants had been asked what electrolyte supplements they planned to use, how often they planned to take them and what their drinking strategy was — whether they planned to drink at regular intervals or just when they got thirsty. They reported their previous training programs and were weighed in. At the finish line, before hydrating or resting, researchers once again weighed them and asked how closely they followed their plans for drinking and taking supplements. A blood sample was also taken to measure sodium levels.
“People have different strategies in these races,” Lipman said. “Some people take a salt tablet every hour. Some prefer to put the supplements in one water bottle, then alternate with a bottle with just water. Some like a diluted mixture with powder or tablets. 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. ”
Sodium’s essential roles
Sodium plays several essential roles in the body, such as maintaining blood pressure and regulating the function of muscles and nerves. Keeping sodium levels in balance while exercising is particularly important to prevent a variety of problems, including nausea, muscle cramping, dizziness and fatigue. Both high and low levels can cause these symptoms.
Past evidence has shown that electrolyte supplements don’t protect against EAH. Usually, the disorder is caused by drinking too much while exercising, which dilutes salt levels. “The reality is dehydration is not as dangerous as overhydrating,” Lipman said. “Dehydration and hypernatremia can cause similar symptoms to EAH, which can be easily confused, especially in the heat, but it’s rarely fatal.”
Analysis of the data showed that 41 of the athletes had sodium imbalances by the end of the race: 11 were found to have EAH due to too little sodium, and 30 were dehydrated, with too much sodium in their blood. Also, 88% of the sodium imbalances recorded occurred during the hot races, indicating that heat and hydration levels were far more predictive of sodium imbalances than either the manner or type of electrolyte supplements taken. Each of the participants took supplements, although the type, amount and manner of ingestion showed little to no effect on sodium levels.
“Overhydrating can reduce electrolyte levels, and electrolyte supplements aren’t going to protect you,” said Lipman. “You have to be smart while exercising, especially in the heat when you are sweating more and have greater hydration requirements.”
Further analysis of the data also showed that participants with EAH had, on average, shorter training programs, weighed more and took five to six hours longer to complete the race. Researchers concluded that running in hot temperatures was an independent risk factor for illnesses from sodium imbalances, avoidance of overhydration was the most important factor in preventing EAH, and avoidance of dehydration prevented hypernatremia.
Burns said that this study raises questions about what exactly are the benefits of electrolyte supplements, but he still plans to keep using them during athletic competitions until more research is done.
And, as Lipman said, “Listen to your body. Stop drinking if you feel bloated or nauseous.” Drink to thirst, not at regularly scheduled intervals, he said.
Other Stanford co-authors are Carrie Jurkiewicz, MD, assistant professor of emergency medicine, and Anne Walker, MD, emergency medicine physician.
Researchers at the University of Colorado-Boulder, the University of New Mexico-Albuquerque, Oregon Health Sciences University, Massachusetts General Hospital and the University of Washington-Seattle also contributed to the work.
The researchers were supported with a travel stipend by the 2017 and 2018 RacingThePlanet research grant.
