Excess or deficit hydration can be fatal for marathon runners, says expert

In a long-distance race such as a marathon, proper hydration is key to running your best. While adequate hydration helps to improve your performance, an excess or deficit of it can lead to fatal consequences.

Marathon is an extreme-level endurance exercise where a runner runs for hours depending on the distance he needs to cover. When muscles contract vigorously, heat is generated. This heat needs to be dissipated. The heat regulation centre of the body, thus springs into action. It increases blood flow to the skin from where the heat is dissipated to the environment through sweat, radiation or convection. If the surrounding temperature is low, the heat may get dissipated through radiation and convection. However, if the environment is warm and humid, then the primary mode of heat dissipation is sweat. Depending on an individual’s genetic structure, clothing and environment, the sweat rate may be excessive or minimal.

Runners are prone to dehydration because of sweating excessively, especially when they run in warm and humid climatic condition. For example, in a city like Mumbai, where the climate can be best described as moderately hot with a high level of humidity, runners are at a greater risk of dehydration. Dehydration leads to loss of both water and electrolytes. Excessive loss of water (loss of  body weight by more than two per cent) and electrolytes during running, leads to muscle cramps and decreases the performance level. Running in severely dehydrated condition can lead to excessive core heat which can further lead to heat stroke and rhabdomyolysis (a syndrome resulting from the breakdown of skeletal muscle fibres with leakage of muscle contents into the bloodstream). This can cause acute kidney failure and kidney shutdown with little or no urine flow. These are serious health conditions which may lead to serious consequences.

Santosh Kumar Dora Senior Cardiologist, Asian Heart Institute, Mumbai

So, it is ideal to drink around 500 ml of water two to three hours before marathon and keep drinking 100 to 150 ml of water every 15 to 20 minutes during the marathon. It is good to drink water whenever you feel thirsty, so as to avoid dehydration.

The opposite to dehydration is overhydration. The body experiences overhydration when the runner drinks excess water during the marathon. A common indicator of overhydration is when the measured body weight after the event is more than the body weight before the event. It happens especially to small height and bulkier people who run slow but drink more water. Overhydration is not as common as dehydration but has serious health risks. Overhydration leads to a condition known as hyponatremia. This is due to the dilution of the electrolytes because of excess body water. Symptomatic hyponatremia can occur when the serum sodium level drops below 130 mEq/L. The usual symptoms are headache, vomiting, confusion, restlessness, disorientation and undue fatigue. If the serum sodium levels drop more rapidly (below 120 mEq/L) then it may lead to serious health hazards such as convulsion, coma and in some cases even death.

Thus, it is advisable to drink less and drink at longer intervals for the persons who run slow. Drink to thirst rather than drink to max.