When endurance athletes exercise for a long time, their bodies sometimes release a hormone that tells the kidneys to hold onto water — even when they don’t need to. This can dilute the salt in the blood and lead to a dangerous condition called hyponatremia, kind of like a known medical syndrome caused by too much of that hormone.

Even if endurance runners take in a lot of salt, they can still develop low blood sodium if they drink too much water — it’s the overdrinking, not the salt intake, that’s the main problem.

Drinking too much fluid during long workouts can actually be dangerous — it can lead to a serious condition called low blood salt (hyponatremia), especially if you're gaining weight during a race because you're taking in more fluid than you're losing.

Some athletes who do long, tough workouts like marathons or triathlons can end up with low sodium in their blood — a condition called exercise-associated hyponatremia — and it’s actually pretty common depending on the event.