During my research, I was also astonished by learning about how too much water can cause the kidneys to become overloaded and shut down and if not treated then eventually could lead to death.
In terms of the amount of sodium intake one should ingest on a daily basis, the basic understanding is that too much sodium will cause the body to withhold water that may have implications on one's overall health when referring to conditions such as high blood pressure.
Therefore, the rationale is to cut back on salt in any form to daily levels below 2400mg. However, the research is different for athletes based on their activity level and the environment that these athletic events take place.
Athletes are encouraged to begin exercise well hydrated and to consume sufficient amounts of appropriate fluids during exercise to limit water and salt deficits (Maughan, & Shirreffs, 2008).
Available evidence suggests that many athletes begin exercise already dehydrated to some degree, and although most fail to drink enough to match sweat losses, some drink too much and a few develop hyponatremia - a condition that affects the way the kidneys excrete water (2008).
There is a tendency to replenish the water due to the initial sensation of thirst and by then the body is severely dehydrated. The athlete then tries to make up the perceived deficit by ingesting fluids over a shorter period of time, which leads to the stated condition.
A water loss equivalent to 2% or more of body mass appears to reduce endurance exercise performance in both temperate and hot environments especially when the duration of the exercises is around 90 min or more. It has been reported that oral replacement of even 50% of a 4% body mass loss during a 20min break was effective in restoring exercise capacity (2008).
According to Anastasiou, Kavouras, Arnaoutis, Gioxari, Kollia & Botoula, exercise-associated hyponatremia may result in confusion, disorientation, nausea, vomiting, pulmonary edema, cardiorespiratory arrest, coma, and even death (Anastasio, Kavouras, Arnaoutis, Gioxari, Kollia, Botoula, et al, 2009).
A study is done involving thirteen healthy, physically active, untrained men (age = 24.5 ± 2.1 years, height = 178 ± 8 cm, mass = 77.9 ± 10.4 kg. body fat = 17.4± 5.4%) (2009).
The purpose of the study was to examine the effectiveness of drinks with different sodium concentrations in maintaining plasma volume and preventing hyponatremia during long-duration exercises in the heat when fluid supplementation matches fluid lost to sweating (2009).
As of 2007, The American College of Sports Medicine suggested that fluid intake during prolonged exercise should be sufficient to limit body mass loss to less than 2% body mass pre-exercise.
Therefore, water should not be ingested to the point that they gain body mass during exercise, but those principles do not apply to the athlete that is already dehydrated before beginning exercise.
Individualized strategies have to made to educate athletes on how to hydrate before, during and after intense endurance activities. No single recommendation will work for everyone.
Anastasiou, C. A., Kavouras, S. A., Arnaoutis, G., Gioxari, A., Kollia, M., Botoula, E., et al. (2009).
Sodium Replacement and Plasma Sodium Drop During Exercise in the Heat When Fluid Intake Matches Fluid Loss.
Journal of Athletic Training 44(2), 117-123.
Maughan, R. J., & Shirreffs, S. M. (2008).
Development of individual hydration strategies for athletes.
Int J Sport Nutr Exerc Metab, 18(5), 457-472.