Too much water could be dangerous

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Drink eight glasses of water a day to stay healthy and hydrated. 

You have heard this throughout your life so it must be correct, right? Maybe not. 

Research by Professor Tim Noakes found the following:

1. The intensity of the exercise leads to a rise in body temperature, not a lack of water
According to Professor Noakes, research has revealed that dehydration is not the major factor in hyperthermia or heat illness. In fact, heat stroke can occur even when the athlete is well-hydrated. Who’s at risk for heat illness? People running as fast as possible, even if they’re adequately hydrated. The faster you run, the more body heat generated. This happens particularly in shorter distance races. Heavier runners, walkers, and hikers are also at risk. The fatter and heavier the person, the more heat will be generated by his body.

2. Don’t worry too much about dehydration
Becoming dehydrated to the extent that modern runners usually do, carries no documented medical risk. You get a bit thirsty and have a dry mouth, but that’s it, says Noakes. According to Noakes, the body is adapted to conditions of mild dehydration. “We evolved from hunters; we had to run and chase animals. We didn’t have time to pause for a drink! Physiologists who didn't understand either humans’ prehistory or the history of running then came along with the unproven hypothesis that to become even the slightest bit dehydrated during exercise would kill you. And then the sports drinks industry in America used this non-existent science to market their products.”

3. Too much water can do more harm than good
Doctors at major marathons around the world are hospitalising more people as a result of overdrinking, and there have been some deaths from hyponatremia, commonly known as water intoxication. This condition means too much water in the blood and very low levels of sodium (less than 130 mmol/L). These athletes didn’t need salt to make them better, so they weren’t salt deficient, but purely water overloaded, Noakes says. When you sweat, you lose water and salt (sodium chloride). You need a minimum level of sodium (and other electrolytes) in your blood to sustain cell function. Drinking litres of water before, during or immediately after the race will not solve the problems caused by loss of water and sodium through sweating. In fact, drinking more water will dilute the sodium concentration even more. You need to get rid of the excess water (though urine), and replete your sodium stores with salty snacks, a salt tablet, or drinking fluid with sodium.

Recognise the signs of water intoxication
It causes the body and brain to swell. The pressure of the brain against the skull increases, leading to convulsions, heart failure and cessation of breathing. Water intoxication can mimic the signs of heat stroke such as nausea, vomitting, extreme fatigue, respiratory distress, dizziness, confusion, disorientation, coma and seizures.

Watch out for:

  • A progressively worsening headache.
  • Body temperature rising higher than 39.9 degrees C during or immediately after exercise.
  • Swelling of the hands and feet.
  • Coughing pink, frothy sputum.

Good to know 

  • Elite runners should drink between 200ml to 800ml per hour. Slower runners are less likely to overheat and should only drink when really thirsty. 
  • When training for the long race, up your salt intake in the days leading up to the race by adding table salt to your food and water. 
  • If you run or walk longer than four hours, increase your salt intake with a salt tablet or a drink with a high concentration of sodium. 
  • Eat salty snacks (like pretzels) before, during and after a long walk and refrain from drinking excess water immediately after the walk. 
  • Drink a large glass of water one to two hours before a long walk or run. 
  • Weigh yourself immediately before and immediately after your training walks. Gaining weight during the walk is a sign of developing water intoxication, and for you to decrease your fluid intake, and increase your salt intake. Losing weight is a sign of dehydration, which is quite harmless.
  • Pain relievers like paracetamol, aspirin and non-steroidal anti-inflammatory drugs may contribute to water overload. Discuss this with your doctor if you use this medication for a condition. Otherwise, avoid them before and during your long walks. 
  • Women are smaller and need even less fluid, and generally run slower, and therefore don’t sweat as much as heavier men running even at the same speed.

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