Optimizing hydration for great race performance by Dr Ryan Paterson
In ultra-distance racing communities, it is well understood that low-hydration (hypo-hydration) can led to decreased aerobic performance. Many people made the logical jump, concluding that more hydration must therefore be better. This lead to an increase in people suffering from over-hydration and subsequent low sodium and electrolyte blood levels. Many guidelines then began to recommend the consumption of sodium (and other electrolytes) during extended exercise to replace the losses of sodium (and other electrolytes) in sweat and to improve thermoregulation (the regulation of heat in the body).
Exercise associated hyponatremia (low-sodium) (EAH) is one of the most significant, possible medical conditions among endurance athletes. Occurrence rates are less than 1% whether the event is a marathon or ultra-marathon, but the rates are increasing. Since 2014, 12 deaths have been reported in endurance athletics due to severe, low-sodium EAH. According to the medical literature, the biggest risk for EAH is consuming, approximately double the amount of fluids during a race when compared to athletes without EAH. In other words, drinking too much. Often the first symptoms of EAH are weight gain with decreased urine output. The continued intake of fluids can lead to nausea, vomiting, confusion and possibly death. Although it would be reasonable to assume that the consumption of sodium supplementation would help prevent EAH, recent research has shown that this supplementation is likely not necessary and not beneficial.
A quick summary of the relevant medical literature: A 2002 study by Speedy et al. showed that in Ironman triathletes who lost weight during the race, sodium supplementation was not necessary to prevent the development of hyponatremia (low sodium). Another study, by Hoffman et al. in 2015, of participants in a 161km ultra-marathon at temperatures of 39c, concluded that exercise-associated muscle cramping, dehydration, hyponatremia, and nausea or vomiting during exercise up to 30h in hot environments are unrelated to total sodium intake, despite a common belief among ultra-marathon runners that sodium intake is important for the prevention of these problems. In a study by Earhart et al also in 2015: High-dose sodium supplementation did not appear to impact (heat regulation), or physical performance in trained, endurance athletes.
While this is the current state of medical understanding, individual variation is a real factor. Many ultra-distance athletes have experience with salt tablets or other forms of electrolyte supplementation that works for them as individuals. While sodium and electrolyte supplementation may not be necessary or beneficial, experimenting during training to find the right combination for your race and recovery is of utmost importance. Interpret professional guidelines for the use of sodium during exercise with caution. It is possible to "train your sweat glands" by training in the conditions you will be racing. As sweat glands become "trained", the electrolyte content of the sweat will decrease and the water content will increase. It is our recommendation that athletes train, to the best of their ability, in the conditions they will be racing and with the electrolyte/hydration plan they plan to use during the race.