Too much of a good thing can kill you!


Overhydration occurs when an excessive amount of water is consumed. In severe cases this can lead to water intoxication and hyponatraemia, a condition defined as a ‘less than normal concentration of sodium in the blood’. Hyponatraemia, resulting from overhydration in athletes, is a cause of exertion-related collapse in endurance athletes that can be potentially fatal.

Research confirms the importance of electrolyte balance and replacing fluids before, during and after strenuous exercise to avoid dehydration. Yet, it is also important to consider the harmful effects of ingesting too much fluid.

In the past the recommendation for endurance athletes was to drink as much as possible during exercise. With new research proving that the recommendation should be revised, the debate now surrounds the issue of optimal fluid intake for athletes. Each person perspires at a different rate depending on his/her environment, exercise intensity, equipment, and body weight. It is advisable, therefore, for athletes to hydrate based on individual needs and not to exceed 800 ml per hour. Sodium is primarily extracellular (exists outside cells), whereas potassium is primarily intracellular (exists inside cells). Water moves across cell membranes until extracellular and intracellular osmotic pressure is equal. In cases of hyponatraemia the low sodium levels allows fluid to flood to the outside of the cells causing swelling of the brain and neurological disorders.

Main Cause

Overhydration leading to hyponatraemia in athletes is caused primarily by the increased intake and retention of water, and worsened by excessive sodium loss through perspiration. It can be experienced after an endurance event when a sudden absorption of fluid occurs after exercise has ceased. This further dilutes the levels of sodium in the blood. Since signs and symptoms of hyponatraemia are similar to those of heatstroke, the condition can be easily misdiagnosed. Early symptoms include; nausea, vomiting, headache, lethargy and fatigue. More advanced symptoms include dizziness, poor athletic performance, muscle weakness, muscles spasms, restlessness, irritability and confusion. Without immediate treatment, seizures and coma may occur as sodium approaches critical levels in the body.


A Doctor should be consulted to correctly diagnose and treat this condition. It may involve a physical examination and a urine and blood test to diagnose the condition and treatment will vary depending on the severity of the condition. Regardless of whether hyponatraemia is acute or chronic, the key to successful management is frequent monitoring of sodium and all electrolyte levels in the blood.


Depending on the individual exercise type and intensity, sweat rates can vary from extremely low values to more than three litres per hour. With large volumes of fluid ingestion, even measured to meet the individuals fluid needs, additional sodium intake is still vital. An increased beverage concentration (1.7 to 2.9gms of sodium chloride per litre of water) may be beneficial. If insufficient fluids are taken during exercise, sodium is necessary in the recovery period to reduce the urinary output and enhance the body’s ability to restore a healthy fluid balance. Each person has a different volume of fluid that can be tolerated and rate of absorption. The rate of fluid loss through perspiration and urination may be less than or exceed the capacity of the digestive tract to assimilate fluids. Individual tolerance, therefore, may dictate the maximum rate of fluid intake. During training, it is important to also practise drinking, as it may enhance your fluid tolerance.

Our Pharmacists and Sports Nutritionists are always available to give you the necessary advice, suggest favourable options for your particular needs and recommend suitable sports drinks or Electrolyte-drink powders to help prevent hyponatraemia. We do urge you to consult your doctor though, if you have experienced any of the signs or symptoms mentioned when training. Only the proper test procedures will determine accurate treatment, so don’t take any unnecessary risks. If you’re in it to win it, make sure you get to enjoy rewards. Which are never worth dying for, by the way.