Anyone that has ever participated in vigorous exercise in the heat, due to athletics, recreational endeavors, or otherwise, has learned about the necessity of staying adequately hydrated.

When you workout, you sweat. Your body reacts this way to regulate its core temperature. As sweat is secreted by glands on the surface of the skin, the air moving across the skin evaporates the sweat into the air. It is through the process of evaporation that the body can cool itself.

Sweating is essential for our survival in the heat. Could you imagine what it would be like if we were unable to sweat? Anytime our core temperatures increased, we would end up panting like dogs (they cannot sweat) and being miserably hot.

Sweat is made up mainly of two substances, water and sodium. The sodium is what makes our sweat taste salty, our eyes sting when sweat gets in them, and our skin get crusty after all remaining sweat evaporates following exercise. The water portion of sweat is what allows it to evaporate, creating the cooling effect we desire.

The problem with the well known method of hydration is this: hydrating with water will replace the fluid portion of sweat that is lost while exercising, but will not replace the electrolytes that have also been lost.

Our cells have a delicate balance of electrolytes both outside the cell membrane and within. Sodium is the major electrolyte present in extracellular fluid (fluid outside of the cells), while potassium is the major electrolyte present in intracellular fluid (fluid inside the cells). Each electrolyte is also present on the side of the membrane opposite its major concentration in lesser amounts.

This balance fluctuates slightly, but too high of a concentration of electrolytes on either side of the cell membrane can cause significant water imbalance issues. Long duration exercise, lasting two hours or more, increases the risk of electrolyte imbalances or what is known in this case as hyponatremia (also called water intoxication).

When individuals take part in races such as ironman triathlons, marathons, and ultra-marathons, they are active for hours on end, and therefore also sweating for extended periods. If these individuals consume only water (with no added salt or electrolytes), electrolyte imbalances begin to form, as sodium levels drop considerably.

Sweat removes a great deal of sodium from the blood stream and extracellular fluid, and hydration replaces only the water. Because of this, the extracellular fluid's volume is maintained, but its electrolytic concentration is not.

The intracellular fluid steadily becomes more and more concentrated in relation to the extracellular fluid. Water is drawn to a stronger concentration, and in extreme cases will start to permeate cell membranes to dilute the intracellular fluid of the cells, all in an effort to restore electrolyte balance.

When this occurs, it is quite similar to filling a water balloon with too much water. The water seeps in, and as the cell membranes are pushed past their holding capacity they may burst, leading to serious health complications.

Symptoms of hyponatremia include nausea, vomiting, headache, confusion, and in extreme cases, loss of consciousness and even death.

The good news is that hyponatremia is an extremely preventable illness.

Individuals who plan on exercising for durations of longer than two hours should plan on consuming beverages that contain both water and electrolytes. Even adding a slight amount of salt to water bottles can do the trick.

Another way to prevent this illness is to monitor overall fluid intake. When running a marathon, stop at every third mile for a quick drink instead of every mile. This will drastically reduce any risk you have of experiencing hyponatremia, as it will keep the volume of water you consume lower, maintaining your electrolyte to water ratio much more easily.

When it comes to hydration, it is possible to consume too much water. Although hyponatremia only becomes a major health risk for those participating in long duration exercise that causes profuse sweating, it is essential that everyone learns about this illness in order to keep themselves safely hydrated, electrolytes and all, during all of their future exercise endeavors.