Any serious athlete or gym rat can tell you that a workout drains you of fluids and electrolytes. Losing too many electrolytes, like sodium, can lead to dangerous health consequences. And many times, intense electrolyte loss occurs from sweating. In a new study, a group of Spanish researchers have found that though everyone loses sodium and moisture when they sweat, some people lose electrolytes faster than others.

When most people hear electrolytes, they probably think of Gatorade. This is for good reason — the popular sports drink is packed with sodium, potassium, calcium, and magnesium. Electrolytes are necessary for regulating the amount of fluid in your body, but they also help with managing acidity in your blood, muscle function, and regulating nerve function. When the body tries to cool itself by sweating, you lose these vital minerals.

People perspire during most physical activities, but during endurance and ultra-endurance events like marathon races, the body can lose several liters of sweat. Because of this, researchers at the Exercise Physiology Laboratory at Camilo Jose Cela University decided to analyze how sodium lost from sweating during a marathon impacts the conditions that allow the body to function properly.

“We do not only lose fluids when we sweat — which can be replaced with beverages — but the levels of several electrolytes that are essential to fluid balance and neuromuscular functioning also decrease — especially sodium,” said Beatriz Lara, the main author of the study and a researcher at Camilo Jose Cela University.

When this excessive loss is not remedied with food or beverages, sodium concentration in the blood drops. When it drops to abnormally low levels, hyponatremia can occur. In severe cases, the condition can cause loss of consciousness, hallucinations, coma, and even death. The current study demonstrates the importance of maintaining the correct electrolyte levels during a race to prevent not only decreased performance, but health complications as well.

The researchers placed two patches designed to collect sweat on 51 marathon runners, who wore them for the entire race. Immediately after crossing the finish line, the runners gave a blood sample for analysis of electrolyte levels. The researchers grouped runners into three categories depending on the sodium concentrations of their sweat: low-salt sweaters, typical sweaters, and salty sweaters. Analysis revealed that the runners with high concentrations of electrolytes in their sweat had lower electrolyte levels in their blood — despite having properly rehydrated and eaten the same amount of food as the other runners.

This data suggests sweat’s electrolyte levels can affect water and electrolyte homeostasis throughout the duration of the marathon. “Electrolyte concentration in sweat is an essential factor for predicting sodium requirements during sports activities, especially endurance activities such as marathons,” Lara said. “It is likely that individuals with very salty sweat would benefit from oral supplements such as salt tablets.”

Source: Lara B, Salinero J, Areces F, Ruiz-Vicente D, Gallo-Salazar C, Abian-Vicen J, et al. Sweat sodium loss influences serum sodium concentration in a marathon. Scandinavian Journal of Medicine & Science in Sports. 2016.