In the 1998 New Zealand Ironman triathlon, 18 percent of finishers were diagnosed with hyponatremia. This trend is becoming more and more common. The reason: environment + salty sweaters + high sweat rate + improper nutrition.
Hot and humid environments can contribute greatly to the success of an athlete finishing the triathlon or not. This type of environmental stress combined with an athlete’s quantity and quality of sweat can spell trouble for the athlete and is certain to result in hyponatremia unless a sound nutrition plan centered on proper fluid and sodium intake is followed.
What Is It?
Hyponatremia is a disorder in fluid-electrolyte balance that results in an abnormally low plasma sodium concentration. Symptoms include:
- Gastrointestinal discomfor
- Nausea and vomiting
- Throbbing headache
- Respiratory distress
- Brainstem herniation
Physiological Ranges of Plasma Sodium
- Normal: 136-142 mmol/L
- Mild: 125-135 mmol/L
- Severe: <125 mmol/L
The risk of developing complications from hyponatremia depend somewhat on the measured level of plasma sodium in the body. There have been many studies that have measured these ranges during and after exercise, and although the physiological ranges of plasma sodium will provide the fitness professional an idea of the severity of hyponatremia, the numbers do not always tell the whole story.
For example, athletes have survived hyponatremia when their plasma sodium concentration was in the “severe” category and others have died when their levels were above the “severe” category. There is no rhyme or reason to this; however, understanding the condition and the athlete will help. When working with an at-risk athlete, it is important to factor these variables into the overall nutrition plan:
- Length of training or race
- Sweat rate (i.e. heavy or light sweater)
- Sweat sodium content (i.e. salty or non-salty sweater)
By knowing these three things ahead of time, the fitness professional can provide strategies that will help to reduce the risk of the athlete developing hyponatremia. Hyponatremia cannot be prevented during exercise, but the risk can be reduced by proper planning.
There are many factors that can cause hyponatremia, but the most popular is excessive fluid intake. With excessive fluid intake, there is an increased risk of developing hyponatremia because urine production is usually decreased. This reduces the body’s ability to excrete excess water. In addition, sodium loss via sweat is increased, which makes it easier to dilute the body’s sodium content.
While some researchers believe hyponatremia is associated with fluid overload, others believe it is associated with dehydration. What is important to realize is that prolonged sweating can cause significant sodium losses and interdepartmental fluid shifts, as seen with fluid overload and dehydration, may predispose an athlete to hyponatremia. The balance of fluid intake and timing becomes of utmost importance, which is what many researchers can agree upon.
Prevention of hyponatremia must include a combination of identifying athletes who are at-risk and educating these athletes about how to properly plan to try to prevent hyponatremia.
Identification of at-risk athletes should be the first step. That is, you need to determine an athlete's sweat rate and sweat sodium content. If these are high and salty, then the athlete is predisposed to hyponatremia during long exercise sessions, especially in the heat and humidity.
Once an athlete is identified as at-risk or not, education should be the focus. The following strategies should be discussed with the athlete and should be part of his nutrition plan:
- Maintain a diet that has enough sodium (as long as there are no pre-existing medical conditions where salt would be detrimental). Often times, at-risk athletes will consume more than the government recommended 2400 milligrams of sodium per day.
- Consume sodium during exercise. Sports drinks, pretzels and possibly salt tablets or powders will work; however, the athlete should be cautioned when using salt tablets or powder. Interdepartmental fluid shifts can be seen when too much sodium is introduced into the body without adequate fluid. Hyponatremia can develop as a result of too much sodium without enough fluid.
- Drink accordingly based on sweat rate. If the athlete does not know his sweat rate, general recommendations include drinking seven to 10 ounces of a sports drink every 10 to 20 minutes. If the athlete has had his sweat rate measured, then a more specific fluid and sodium intake plan can be made.
- Avoid overdrinking. The athlete must adhere to his fluid and sodium intake plan that has been predetermined, and he must understand the importance of drinking too much. Gaining weight during exercise is a sure warning sign of excessive drinking.
- Limit pre-hydration. This can lower blood sodium before the event begins and already puts the athlete behind in his sodium intake plan. It is recommended that the athlete consume 17 to 20 ounces of sports drink two to four hours before exercise and seven to 10 ounces 10 to 20 minutes before the start of exercise.
- Don’t over drink after training or competition. Weight loss of one to two pounds from the beginning to the end of the exercise bout indicates dehydration. At-risk athletes should get into the habit of weighing before and after exercise to determine their fluid needs afterwards. Athletes should drink 20 to 24 ounces of sports drink for every pound lost during the event. It is important that this is a sports drink because the sodium present in a sports drinks helps to facilitate the entry of glucose and water into the cells. Without sodium, the body cannot fully absorb the glucose and water.
Knowing the inherent risks and symptoms of hyponatremia is important when working with athletes. Identifying athletes who are at-risk for becoming hyponatremic is extremely important and proper education strategies can be developed based on whether or not they are a heavy and/or salty sweater. Sports drinks should be favored over water during exercise in order to provide the athlete the necessary fluid, carbohydrates and sodium. The flavor of sports drinks is formulated so that the athlete wants to drink more and therefore constantly re-hydrates and replenishes the sodium lost through sweat.
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National Athletic Trainers’ Association Position Statement: Fluid replacement for athletes. J Athletic Training. 2000;35:212-214.
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