There have been two instances recently of the death of female runners in mass-participation marathons in the US, and one in the UK where the death has been attributed to hyponatraemia. This is a serious condition where excessive water intake causes a loss of sodium from the blood, with potentially fatal consequences. The condition is particularly dangerous because the symptoms can be readily mistaken for exhaustion, or even dehydration leading to incorrect first aid treatment.

What causes it?

The exact mechanisms are not fully understood and I won't go into the complex physiologic pathways of sodium and water balance. The simplest answer isthat lost sweat (salt and water) is replaced by ingested water (no salt). This dilutes the sodium in the bloodstream, and hyponatraemia results 

What are the symptoms of hyponatraemia?

The spectrum of symptoms can range from mild to severe and can include nausea, muscle cramps, disorientation, slurred speech, confusion, and inappropriate behavior. As it progresses, victims may experience seizures or coma, and death can occur. Severe hyponatraemia is a true medical emergency

Fluid lost in sweat must be replaced, otherwise your body will become dehydrated (short of water) and less efficient. Alcoholic drinks and drinks containing caffeine – such as tea and coffee – can be dehydrating. Take plenty of non-alcoholic drinks with you when you run, especially when training in hot weather. Drink enough to keep your urine a pale straw colour. Also, drink plenty of liquids after training – especially after long runs – and practise drinking during longer training runs. You could also try drinking sports energy drinks in training to see if you like them.
Drink plenty of fluids and preferably no alcohol in the two days before a race. DO NOT drink excessively before, during or after a race, as you may get hyponatraemia (see ‘Drinking Safely’ below).

DRINKING SAFELY
A balancing act

Drinking too little can lead to problems, as you will always need to replace some of the fluid you lose as sweat. On the other hand, drinking too much can be very dangerous and lead to hyponatraemia (water intoxication), fits, and in some cases death. Drink when you feel the need and DO NOT gulp large volumes of fluids before, during or after a race.

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