While preventing dehydration by ensuring adequate fluid intake during exercise is important, there is a flip side to this that needs to be considered. Drinking too much is also possible and can lead to “hyponatremia.” Hyponatremia is low blood sodium concentrations. While many athletes with hyponatremia will have no symptoms, if severe enough, it can cause nausea, loss of consciousness and even death.
While hyponatremia can occur in athletes in all sports and at all levels of competition, it is more likely to occur in endurance events undertaken in cool temperatures with a high availability of fluids during the event. Athletes most at risk are those performing at a low intensity with an excessive fluid intake. While again, hyponatremia can happen to any athlete, female athletes with a low body weight seem to be at a higher risk.
The main cause of hyponatremia is excessive fluid intake rather than insufficient sodium intake to replace sweat losses. To prevent hyponatremia, athletes should not be drinking so much fluids that they’re weight increases from pre to post exercise. In fact, a weight loss of 1-2% during prolonged exercise is completely acceptable and unrelated to sweat losses.
The repeat theme continues — more is not always better. While we should be drinking enough to prevent dehydration, the competition or training situation needs to be considered. If it’s a cool day and you’re performing at a low intensity, you may have little sweat loss and as a result, will have low fluid needs during exercise.
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