Nearly every runner took salt, and sodium still fell too low
In a 161 km mountain ultramarathon, 94 in 100 runners took salt capsules and one finisher in fifteen still ended below the line. How much they took did not separate them.
What the study found
Nearly every runner took salt, and low blood sodium happened anyway
The comparison is more salt against less, not salt against none. In a 161 kilometre mountain ultramarathon, 94 in 100 runners took salt capsules and one finisher in fifteen still ended below the line, with the amount taken not separating them. Five desert ultramarathons found the same.
The caveat · Runners picked their own salt dose
Nobody was randomised: runners chose their own salt and their own drinking, so everything else they did differently comes along with the comparison. Intake was reconstructed from a questionnaire filled in after the race. Almost everyone supplemented, 94 in 100, which leaves barely any unsupplemented group at all, so this says more salt did not protect rather than that salt does nothing. Self-selected ultramarathon fields, single races.
What we don't know
Whether deliberately taking salt changes the risk of low blood sodium in endurance races is untested. Nobody has randomised runners to salt or none, because in these races almost everyone already takes it.