For many years, even decades, we have been told to continually hydrate during activities like running. The fear has been that without constant hydration, one would dehydrate and have cramps or poor performance. However, recent studies have started to disprove this traditional teaching.

Too Much Water May Be Harmful

Athletes that hydrate constantly and take in too much water are at risk not only of poor performance but of severe health issues and even death. It is more likely to be harmed by too much water than it is by too little water. The human body is designed to regulate its water needs closely; a runner will feel thirst when the body needs more water. Water needs will change depending upon the event and the climate. A runner performing a marathon in the desert will need more water than a runner doing a marathon in Boston in the winter; the first runner will likely feel thirst more often as well. Too much water intake will dramatically alter the electrolyte balance in the runner’s bloodstream. Hyponatremia, too little salt in the blood, can cause delirium and weakness. This electrolyte problem stems from dilution of the blood from too much water intake; this can cause brain swelling and death. If you are a slower runner, you are more likely to drink at each rest station and this may be detrimental. The body has a finely balanced system that takes what is absorbed by the stomach and intestines and uses it and excretes waste water by way of the kidneys. If you drink too much and overload the ability of your kidneys to excrete the water, it will build up in your tissues and bloodstream.

Mild dehydration does not hurt performance and may actually help it.

A low level of dehydration is not actually harmful. About 3% dehydration is thought to perhaps even help. Letting your system, or body, notify you when it is time to take in more water is helpful; in other words drink when thirsty. Distance runners often lose water weight while running an event. The ones that lose the most tend to be the faster runners; a study of runners in a marathon found that the faster finishers lost a higher amount of weight than did the slow finishers. Lighter runners can run faster. On physician found that elite triathletes can have 12% dehydration levels during the events. Bear in mind that official recommendations are to maintain a dehydration level of only 2% or less. Becoming dehydrated may result in dizziness, decreased urination, muscle fatigue, poor concentration, rapid heart rate and longer recovery from a run. Then again, the symptoms of overhydration are nausea/vomiting, headaches, confusion, muscle weakness or cramps, seizures, unconsciousness and coma. Basically, it is wise to use common sense and this is supported by some research. If you drink too little or too much, you will not run as well as if you drink just enough. We have a great way to understand if one is drinking’ just enough’; the body tells you when to drink by causing thirst. Listen to your body. Select references:

1. Noakes, T. Waterlogged: The Serious Problem of Overhydration in Endurance Sport. Champaign, IL: Human Kinetics; 2012.
2. Rosner, MH, Kirven J. Exercise-associated hyponatremia. Clinical Journal of the American Society of Nephrology, 2007;2(151-161).
3. Goulet, ED. Effect of exercise-induced dehydration on endurance performance: evaluating the impact of exercise protocols on outcomes using a meta-analytic procedure. British Journal of Sports Medicine, 2012.
4. Wyndham CH, Strydom NB. The danger of an inadequate water intake during marathon running. South African Journal of Medicine,1969; 43(893-896)
5. Armstrong, L. E.; Costill, D. L.; Fink, W. J., Influence of diuretic-induced dehydration on competitive running performance. Medicine & Science in Sports & Exercise 1985, 17 (4), 456-461.
6. Maughan, R. J.; Shirreffs, S. M., Dehydration and rehydration in competitive sport. Scandinavian Journal of Medicine & Science in Sports 2010, 20 (3), 40-47.
7. Noakes, T. D., Lore of Running. 4th ed.; Human Kinetics: Cape Town, 2001.
8. Noakes, T. D., Hydration in the marathon: using thirst to gauge safe fluid replacement. Sports Medicine 2007, 37 (4-5), 463-466