Did you ever think you could drink too much water during a race? Unfortunately, some have and this has lead to a condition known as exercise associated hyponatremia. Hyponatremia is a disturbance in electrolyte balance that is the result of sodium levels in the plasma falling below 135 millimoles per liter of plasma. And at lower levels a condition called water intoxication may set in, which is usually a complication of other medical conditions. To bring some perspective, normal values range between 142-138. Values below 120 can be fatal. This is more common is marathon or long distance triathlon races. The incidence of this condition occurring in a 5k or 10k is virtually nonexistent.
There are a couple of reasons people might have hyponatremia. The first, there is too much consumption of water over too short a period of time. The second is an excessive loss of sodium loss through perspiration. If both factors are present, the risk is exacerbated. Those who sweat at a higher rate are at a higher risk; but excessive fluid intake for a normal sweat rate can also lead to inadequate fluid loss which can also cause hyponatremia. Those who drink too much and do not use the water efficiently, can dilute their plasma sodium level making them prone to the condition. Women are found to lose more sodium than men and have less water to begin with, posing a higher risk for them.
Sign and symptoms of hyponatremia include nausea, vomiting, headaches and confusion. Early signs that you may be hyponatremic include feeling bloated, followed by nausea and vomiting. In severe cases feelings of restlessness, lethargy and confusion can appear. At this level, respiratory distress and seizures may occur and the most advanced stages include rapid swelling of the brain, coma and even death.
So how should you prepare? Keep track of your weight during training. Plan on weighing in and out during the days when you have a long run. Weight loss of more than 2% or any weight gain is a warning signs that justify immediate medical consultation and indicate that you are drinking improperly. You can drink or eat salty foods such as sports drinks which can replace electrolytes, and gels will be able to replace lost calories, carbohydrates and sodium. With an increase in heat and humidity, comes a higher need for salt. You can figure out how much water to drink and replenish by calculating your sweat rate. For this, weigh yourself prior to the run without clothes, exercise for 1 hour in race conditions, then weigh yourself again without clothes. If for example you lost 3lbs, plan on replacing 16 oz per pound. Drink when thirsty during your race, and don’t feel like you have to stop at every watering hole while on the course. Plan your hydration accordingly, and enjoy your next big race!