Please get enough salt and minerals in your diet!
In “Exercise-Associated Hyponatremia in Endurance and Ultra-Endurance Performance–Aspects of Sex, Race Location, Ambient Temperature, Sports Discipline, and Length of Performance: A Narrative Review” Beat Knechtle, Daniela Chlíbková, Sousana Papadopoulou, Maria Mantzorou, Thomas Rosemann, and Pantelis T. Nikolaidis write:
“Exercise-associated hyponatremia (EAH) is defined as a plasma sodium concentration of <135 mmol/L during or after endurance and ultra-endurance performance and was first described by Timothy Noakes when observed in ultra-marathoners competing in the Comrades Marathon in South Africa in the mid-1980s. It is well-established that a decrease in plasma sodium concentration <135 mmol/L occurs with excessive fluid intake. Clinically, a mild hyponatremia will lead to no or very unspecific symptoms. A pronounced hyponatremia (<120 mmol/L) will lead to central nervous symptoms due to cerebral edema, and respiratory failure can lead to death when plasma sodium concentration reaches values of <110–115 mmol/L. The objective of this narrative review is to present new findings about the aspects of sex, race location, sports discipline, and length of performance. The prevalence of EAH depends on the duration of an endurance performance (i.e., low in marathon running, high to very high in ultra-marathon running), the sports discipline (i.e., rather rare in cycling, more frequent in running and triathlon, and very frequent in swimming), sex (i.e., increased in women with several reported deaths), the ambient temperature (i.e., very high in hot temperatures) and the country where competition takes place (i.e., very common in the USA, very little in Europe, practically never in Africa, Asia, and Oceania). A possible explanation for the increased prevalence of EAH in women could be the so-called Varon–Ayus syndrome with severe hyponatremia, lung and cerebral edema, which was first observed in marathon runners. Regarding the race location, races in Europe seemed to be held under rather moderate conditions whereas races held in the USA were often performed under thermally stressing conditions (i.e., greater heat or greater cold).
“For years, exercise-associated hyponatremia (EAH) has been well-known among endurance and ultra-endurance athletes. Unfortunately, the occurrence of EAH continues to spread into a wider variety of sports and cause deaths in otherwise healthy individuals . Athletes continue to die from complications associated with hyponatremic encephalopathy. In 2007, a 22-year-old male fitness instructor finished the London Marathon, where upon arrival, he collapsed and died due to EAH . In 2015, a 30-year-old age group triathlete died after the Ironman Frankfurt due to EAH with hyponatremic encephalopathy .
“The most likely reason for developing EAH is fluid overload [4,5] with the possibility of developing lung or brain edema [5,6] with fatal outcome . Considering the increased number of endurance and ultra-endurance races, and of finishers in these races during the last years, comprehensive knowledge about EAH would be of great practical importance for athletes and professionals (e.g., coaches, nutritionists, practitioners, exercise physiologists) working with them. It should be highlighted that endurance and ultra-endurance athletes might compete in races differing for distance (e.g., marathon versus ultra-marathon) and under a wide range of environmental conditions (e.g., hot versus cold). Especially, it would be of interest to examine the variation of EAH by parameters such as sex, sport discipline, race distance and environmental conditions.
“EAH describes the occurrence of hyponatremia in individuals during prolonged exercise (i.e., usually longer than six hours) and is defined when plasma or serum concentration of sodium is <135 mmol/L . Apart from the definition of hyponatraemia based on biochemical severity , it can be also diagnosed based on symptomatology, as symptoms have been reported even at concentrations close to 130 mmol/L . This can occur during or after prolonged physical exertion for 4–6 h or longer  and can be detected up to 24 h after the end of the exercise [13,14]. In the mid-1980s, Tim Noakes was the first to report severe symptomatic hyponatremia at the Comrades Marathon held in Durban, South Africa . The Comrades Marathon is a 90-km long road-running race that has been held since 1921 between the South African cities of Durban and Pietermaritzburg. This race is the most traditional and participant-strong ultramarathon worldwide . Hyponatremia was detected in four runners in 1981 and 1985 . Prior to 1981, endurance athletes were advised not to drink during exercise [17,18], which in some cases led to hypernatremia . Due to this knowledge, the American College of Sports Medicine (ACSM) recommended to drink as much as possible during exercise to prevent hypernatremia [17,18,20,21,22]. This advice led to an increased number of cases of EAH, especially in the USA. One major reason for this development was the US beverage industry and their funding of sports research with the aim of drinking as much as possible in order to avoid dehydration, which was measured by a loss in body mass during exercise .”