Thirst for success

There is little doubt that proper hydration has many benefits for physiological function, performance and health.  Good hydration practices follow the general premise that an individual will attempt to match fluid intake with fluid losses. We know that when sweat loss exceeds fluid intake we become dehydrated, although it's a common practice to drink fluids despite a lack of thirst. When athletes are encouraged to consume more liquids than they actually need it can lead to exercise associated hyponatremia, which means a low concentration of sodium in the blood.
 
Severe or life-threatening hyponatremia can occur during exercise and is largely associated with endurance activities such as: marathons, triathlons, and ultradistance races.

Symptoms of hyponatremia are:

• impaired exercise performance
• headache, nausea and vomiting
• seizure (convulsions)
• bloated stomach or swelling of hands, legs and feet
• severe fatigue
• confusion and disorientation

Who is at risk?

• athletes who drink too much before and during prolonged exercise in warm, humid climates
• athletes who sweat a lot or excrete a salty sweat
• those who are overzealous in their drinking habits 

Prevention -  There are many ways to prevent hyponatremia: moderate water intake based on thirst, replace fluids on a schedule, measure and record before and after practice weights, and/or note changes in urine colour.

Although the instances of fatal hyponatremia are rare, evidence suggests that non-fatal hyponatremia is common. It's important that coaches and athletes are aware of the risk factors so they can actively work toward its prevention.

References from the SIRC Collection: 

1. Beltrami F, Hew-Butler T, Noakes T. Drinking policies and exercise-associated hyponatraemia: is anyone still promoting overdrinking?. British Journal Of Sports Medicine. October 2008;42(10):496-501.
2. Burfoot A. Drink to your health: sure, you should drink regularly. But exactly how much water do you need? And why are some runners dying from excessive fluid consumption. Runner's World. July 2003;38(7):52-54;56;58-59.
3. Manasso J. Too much water can be bad, too. ASCA Newsletter. August 2005;2005(8):6.
4. Murray B, Stofan J, Eichner E. Hyponatremia in athletes: "water intoxication" and subsequent death has become a "hot" topic. How dangerous is it?. Marathon & Beyond. January 2004;8(1):77-82;84-86;92.
5. Nolte H, Noakes T, van Vuuren B. Protection of total body water content and absence of hyperthermia despite 2% body mass loss ('voluntary dehydration') in soldiers drinking ad libitum during prolonged exercise in cool environmental conditions. British Journal Of Sports Medicine. November 2011;45(14):1106-1112.
6. Redmon G. Hyponatremia: Water Intoxication. American Fitness. November 2005;23(6):58-61.
7. Shirreffs S, Maughan R. Urine osmolality and conductivity as indices of hydration status in athletes in the heat. / Osmolalite et conductibilite de l ' urine en tant qu ' indices de l ' etat d ' hydratation des athletes sous la chaleur. Medicine & Science In Sports & Exercise. November 1998;30(11):1598-1602.