In the British Journal of Sports Medicine, Professor Tim Noakes, from the University of Cape Town and the leading researcher into exercise hyponatraemia, criticised the sports drink industry for positioning their products to the exercising public as "a medicine that must be ingested to prevent heat illness and optimise sports performance". I believe that the body is adapted for conditions of mild dehydration.
"We evolved from hunters we had to run and chase animals on the hot African plains. We didn't have time to pause for a drink", he says. "Physiologists developed an unproven hypothesis that to become even the slightest bit dehydrated during exercise would kill you. The sports drinks industry then used this bad science to market their products." Runners have died from hyponatraemia*, but Noakes says he "has yet to find a death from dehydration in the history of competitive running".
Found in the Guardian newspaper 19 Aug 2008.
*Hyponatraemia or fluid intoxication is more prevalent than dehydration. Caused by sodium levels and other body salts (or electrolytes) becoming dangerously dilute, hyponatraemia can result in dizziness, vomiting, respiratory problems and fatigue. "During intense or prolonged exercise, the kidneys are unable to excrete fluid as efficiently as normal. In extreme cases, water is retained, especially in highly absorbent brain cells, and the pressure causes the body to shut down its primary functions, such as breathing and heart rate. Treatment involves a small volume of highly concentrated salt solution. But it can be fatal."
In rare cases, it is possible to become overly hydrated while exercising. This condition, known as hyponatremia, is caused by low levels of sodium (salt) in the blood. It can occur when too much water is drunk over a very short period of time.
Hyponatremia sometimes affects athletes whose blood sodium level is reduced through sweat, then further diluted by drinking large amounts of water.
Typical symptoms of hyponatremia include nausea, vomiting and headache. In the most serious cases, the brain swells, resulting in confusion, seizures, coma and sometimes death.