Dan Stumpus writes:

Salt loss in sweat can be 2 to 3 grams per liter.

As a person becomes acclimated, the salt content of sweat drops a great
deal. Conversely, a person who never perspires and then must do so
profusely can lose a great deal of salt.

For ultra runners (I'm one) this is pretty important -- I consumed 7+
liters of Gatorade and water in the last 50 miler I did (and I sweated out a
bit more, being several pounds lighter at the finish). This is a lot of
salt to excrete. I took in about 6 grams of salt suppliments during this
run, and got a small amt from the food and gatorade.

Unless you are measuring your sodium balance carefully, consuming extra
salt can be hazardous. An acclimated individual will produce hypotonic
perspiration, and thus his sodium load will rise with exertion, rather
than fall. Adding salt to this can cause hypernatremia and/or diuresis.

It's important to drink fluids that contain salt in the same
concentration as the perspiration you are losing, no more and no less.
So if your sweat is hypotonic (and it usually is), you don't want to
drink anything saltier than that.

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