Water & Salts

We grew up with the notion that doctors’ standard advice to drink eight glasses of water per day is cast in stone. For years we also believed that we – and particularly runners, walkers, hikers, sportspeople and recreational exercisers - should drink water even before we are thirsty, because by the time we feel truly thirsty, we are already quite dehydrated.
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People believed that dehydration was the single greatest risk to the health of runners because it would cause the body temperature to rise, leading to heat illness, including heat stroke.
Now, almost twenty years after Prof Tim Noakes of the Sport Science Institute of South Africa and the University of Cape Town first challenged this line of thinking, other experts have come to recognise that he was right after all.
Maintaining hydration during periods of physical exertion is key to good performance. While drinking too much water during activities can lead to physical discomfort, dehydration in excess of 2% of body mass (by weight) markedly hinders athletic performance. It is recommended that an athlete drink about 400-600 mL 2-3 hours before activity, during exercise he or she should drink 150-350mL every 15 to 20 minutes and after exercise that he or she replace sweat loss by drinking 450-675 mL for every 0.5 kg body weight loss during activity. Some studies have shown that an athlete that drinks before they feel thirsty stays cooler and performs better than one who drinks on thirst cues, although recent studies of such races as the Boston Marathon have indicated that this recommendation can lead to the problem of overhydration. Additional carbohydrates and protein before, during, and after exercise increase time to exhaustion as well as speed recovery. Dosage is based on work performed, lean body mass, and environmental factors, especially ambient temperature and humidity.
Excess water intake, without replenishment of sodium and potassium salts, leads to hyponatremia, also called water intoxication at more dangerous levels. A well-publicized case occurred in 2007, when Jennifer Strange died while participating in a water-drinking contest. More usually, the condition occurs in long-distance endurance events (such as marathon or triathlon competition and training) and causes gradual mental dulling, headache, drowsiness, weakness, and confusion; extreme cases may result in coma, convulsions, and death. The primary damage comes from swelling of the brain, caused by increased osmosis as blood salinity decreases.