Why Exercisers Need Salt
The key to retaining water during exercise is to take in
salt to replace the salt you lose in your sweat. Until recently,
many scientists did not appreciated how important salt is to
retaining fluid in your body. Thirst is a late sign of dehydration.
You lose water during exercise primarily through sweating, and
sweat contains a far lower concentration of salt than blood. So
exercisers lose far more water than salt, causing the
concentration of salt in the blood to rise. A person will not feel
thirsty until the concentration of salt in the blood rises high
enough to trip off thirst osmoreceptors in the brain and it takes a
loss of between 2 and 4 pints of fluid to do that.
You need to take salt to retain the fluid you drink while
exercising. If you lose two pints of fluid, you can replace it with
two pints of water if you also take salt, but if you don't take salt, it can take four pints of fluid to replace two pints of sweat because the water you drink will pass out through your kidneys.
In one study, female competitive distance runners took in
drinks with different concentration of salt during a four-hour run
(British Journal of Sports Medicine, Volume 37, Issue 4, 2003).
Ninety-two percent of those who took in plain water with no
additional salt developed low blood levels of salt. Taking in fluid
without also taking in adequate amounts of salt dilutes the
bloodstream, so that the concentration of salt in the blood is
lower than that in brain cells. This causes fluid to move from the
low-salt blood into the high-salt brain causing the brain to swell
which can cause seizures and death. Taking in extra salt during
prolonged exercise increases thirst so you drink more fluids, and
prevents blood salt levels from dropping so low that you become
tired, develop muscle cramps, and can even die. You can keep
yourself fresh during extended exercise by eating foods with salt
and drinking frequently, before you feel hungry or thirsty. Once
you feel hungry or thirsty, you will find it very difficult to regain your strength.
Checked 9/29/08