The advice has always been: drink, drink, drink. Drink before you are thirsty. This mantra has always been hammered into the minds of the legion of endurance athletes.
But it seems that drinking too much is a bigger danger than drinking too little. When one drinks too much water the osmolarity of the blood may differ from the body cells causing very serious problems.


In 2007 Jennifer Strange died; she had participated in a contest who could out drink the others by drinking water without having to pee.

In 2008 Dawn Page got brain damage as a result of a water cure treatment because her alternative therapist misinterpreted her worsening condition.

During a ragging a student had to drink a glass of water every time he lost a certain game. He lost quite often which resulted in water intoxication. After an epileptic attack he had to be taken into a hospital emergency department. He survived but it was a narrow escape.

Babies with diarrhea run the risk of water intoxication when they get fluids with too few electrolytes.

XTC-users are also a risk Group. After the pills they have to urinate much and are consequently very thirsty. By uncontrolled drinking of large quantities of water the sodium content of the blood diminishes with sometimes disastrous consequences. The conclusion will then be that XTC use is the cause whereas the real cause is water intoxication.

Endurance athletes and soldiers are also risk groups in their very long races and maneuvers. Certainly in hot weather conditions they lose much water through perspiration and therefore considerable amounts of sodium. By compensating for this loss with only water some problems may arise.

Also marathoners run a higher risk. In 2002 a 28 year old runner died of water intoxication in the Boston marathon. The American Athletics Union has therefore adapted the rules for drinking during races.


Water intoxication is caused by a disturbance of the osmotic process. When the sodium level of the blood diminishes through excessive sweating on the one hand and through the excessive intake of water on the other hand the blood – which is normally hypertonic compared to body cells – becomes hypotonic. This situation causes the course of fluids to go in the opposite direction. The result is that the cells will take up water and swell with all the nasty consequences.


Especially brain cells take up fluids when there is a hyponatraemia causing them to swell. This phenomenon is called a brain edema. The increased brain pressure that arises because there is too little space within the skull vital structures are compressed which may cause headaches, epileptic attacks, loss of consciousness and finally death.

Symptoms of water intoxication

  • Muscle cramps
  • Decreased blood pressure
  • Disequilibrium
  • Feeling of weakness
  • Fatigue
  • Gain of body weight
  • Headache
  • Concentration problems
  • Coma
  • Death because of suppressed breathing

The Boston marathon investigation.

Blood was taken immediately after the marathon. It came out that 13% of the near 500 runners who were in the test had a hyponatriemia; 0.6% of the runners who were sampled met the criteria of a serious lack of sodium.

These data when applied to the total number of participants who finished (15.000) mean that 1900 runners had slight to medium lack of sodium and 90 runners with a serious with a serious deficiency.

Risk factors for hyponatremia:

  • More in women.
  • Gain of body weight during the marathon.
  • A time of over 4 hours in which the participants drank at every stall.
  • A relatively low body-mass index*.

The gain of body weight is caused by excessive drinking during the race, the important factor being the absorption of water in the cells of the body. One runner in Boston had even gained 4.1 kg; it is normally so that runners who finish the marathon lose some weight. A loss of one kilogram is acceptable. When the loss of weight is higher the runner should have drunk more.

It does not matter if athletes drink sports drinks with a little salt to maintain the level of sodium or pure water. The content of sodium is not enough to avoid water intoxication according to the investigators.

An extra danger are the relief workers who misinterpret the situation when a runner passes the finish line stumbling, dizzy and with a headache. Fluid is then the first thing they offer supposing that dehydration is the cause. Fluid intake in such a situation is of course harmful rather than beneficial.

The right treatment for complaints based on a lack of sodium is administering salts through an intravenous infusion. This extracts the water from the cells again.

For dehydration it is mostly sufficient to give a sport drink. For extreme dehydration intravenous administering of fluid is also the most effective treatment.

Making a note of body weight before the start on the runner’s number may supply important information to the relief worker. The organization should see to it that there are enough calibrated scales at the start and finish.

Rule of thumb:

After the finish heavier than at the start: Water intoxication!!!!
After the finish lighter than at the start: Dehydration


In Europe there are drinking stalls every 5 km during the marathon. That is a total of 8 stalls. In the USA there is one every mile, so every 1600 m. This means 26 stalls.

drinking stall marathon
  • 8 drinking stalls
  • 500 ml before the start.
  • One cup at every stall.
  • Estimated fluid intake 2 litres.
  • This is sufficient to compensate for the expected loss of 3 litres.
  • A loss of body weight of 1 kg is acceptable.
  • 26 drinking stalls
  • One cup at every stall.
  • Estimated fluid intake 4 litres.

The standard advice for endurance athletes to drink much during exertions should be reconsidered. The advice ti drink before you are thirsty seems outdated. Fluid intake should be based on the real necessity. This can be determined by weighing body weight before and after workouts. Note the data in a kind of drinking log:

  • Body weight before and after the workout.
  • The duration of the workout.
  • Location: at high altitudes there is more need to take in fluids.


  • weather conditions.
    Dry and hot conditions or high temperatures and high air humidity. Cold.


  • Write down fluid intake during the workout.
  • Keep running when drinking. Do not stop at a stall to pour in a few cupfuls

*Body-mass index, BMI.
Also called the Quetelet Index.

Formula =     Body weight in kg divided by the quadrate of body length in meters.
What is a healthy BMI?
Less than 18.5                  = underweight.
Between 18.5 – 24.9       = healthy weight.
Between 25 – 29.9          = overweight.
Over 30                              = serious overweight, obesity.