Tips and tricks to keep your hydration on track

GU Fuels U: Hyponatremia and the Endurance Athlete
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Overzealous hydration can lead to serious health problems. Learn more from the experts at GU Energy.

By Bryan Bergman, PhD, and Brent Mann, MS

Exercise-induced hyponatremia was first reported in the mid 1980’s; the awareness of exercise hyponatremia, however, increased dramatically in 2005 with a publication in the world’s top medical journal. Untreated, hyponatremia can lead to seizure, coma, and even death. Though hydration is a key component for maximizing performance and performing safely in hot environments, most athletes struggle with adequate hydration. This has resulted in recommendations for high fluid intakes during exercise. This state of diluted blood sodium levels (<135mmol/L) is caused by ingesting liquid in excess, though it can also be caused by abnormal fluid retention by the kidneys.

In 2005, Almond et al. published a paper in the New England Journal of Medicine on the prevalence of hyponatremia during the 2002 Boston marathon. This study showed that of the 488 people providing a usable sample, 13 percent had hyponatremia – making the condition more common than previously thought. This publication put the fear of exercise-induced hyponatremia in the forefront of the minds of race directors, as well as physicians providing medial coverage for endurance events. As a reaction, the governing body for marathon physicians (International Marathon Medical Directors Association) has made a recommendation that individuals “drink to thirst” to avoid hyponatremia during these events.

This recommendation may be appropriate for a six-hour marathoner who exercises at low intensities, has lower rates of heat production and sweating, and more time on the course to drink. However, it could put faster athletes in harm’s way from dehydration and heat stress since they exercise at higher intensities. At the very least, the recommendation to drink to thirst could promote dehydration which has a dramatic effect on exercise performan. Exercise performance is decreased by dehydration resulting from as little as a two percent drop in body weight. If athletes just rely on a sense of thirst to drive fluid intake they may become dehydrated.

There have been many studies documenting the challenges of preventing dehydration during exercise. For most athletes, fluids cannot be consumed during exercise at a rate to match the rate at which fluids are lost. When athletes drink when they feel like it, instead of on a schedule, they become more dehydrated. Studies showing better performance with more hydration during exercise is the basis for recommendations for athletes to drink before they are thirsty, and drink to a schedule (one bottle of fluids per hour, etc.)

In fact, in individuals seeking medical attention after the Boston marathon from 2001 to 2008, under-hydration is almost six times more common than over-hydration. So should a recommendation not to over-drink be globally administered when not drinking enough is a problem faced by 85 percent of participants with fluid balance issues seeking medical attention after a marathon?

It should be every race physician's goal to make recommendations to prevent deaths during events, but these recommendations may prevent individuals from performing to their full potential. We want to provide recommendations for athletes in hopes of preventing both hyponatremia as well as dehydration, heat stress, and poor performance (under-hydration).

Risks for hyponatremia

Let’s explore the two biggest risk factors for hyponatremia during the Boston marathon in 2002 that have also been supported by the American College of Sports Medicine:

1. Weight gain during exercise from over-hydration

This is the single biggest predictor of who may develop hyponatremia during exercise. People who gained weight did so from consuming too much fluid during exercise. To prevent over-hydration, individuals should weigh themselves before and after exercise to make sure they are not gaining weight. Most people will lose weight--the amount of weight lost will give valuable feedback that the athlete is not drinking enough during exercise. Some individuals will gain weight – and that weight gain is most likely from drinking too much. Individuals should adjust the volume of fluids consumed based on feedback from the scale after exercise. Preventing weight gain during exercise should prevent almost all cases of exercise-induced hyponatremia

2. Race time

Individuals who take longer to complete a race are at a higher risk for hyponatremia. This means that the exercise intensity is lower than those who complete the event faster, which translates to less heat production and possibly lower sweat rates. Slower speeds also make it easier to physically drink during running events, in addition to having more time to drink on the course.

Two other factors predisposing individuals for hyponatremia are low sweat rates during exercise, as well as being smaller and less lean.

Factors not important for predicting hyponatremia:

Type of fluid consumed: Sports drinks contain sodium and electrolytes, but they are still much less dense in both compared to our blood (they are hypotonic).  As a result, even sports drinks can promote hyponatremia by diluting blood sodium from over-drinking. So individuals that become hyponatremic are not just drinking water – they are drinking too much of all fluids.

Sex: In the Almond study, it did not matter if individuals were male or female – both were equally at risk. However, others suggest that women may be at greater risk than men. The takeaway from this study is that slower men and women athletes have more time to over-consume water or sports drinks on race day and are at risk for developing hyponatremia. While relatively less probable to occur compared to dehydration, prevention is key to avoid hyponatremia-related illness.

Hyponatremia Q&A

How do you prevent hyponatremia?

Know thyself. Each athlete needs to test hydration strategies during training in order to properly execute race day hydration. Do you lose weight when working out? Gain weight? Do you sweat profusely or hardly at all? Each athlete should know how they respond to exercise, how much they need to drink in order to prevent weight gain, and minimize weight loss during exercise. Every workout before an event is an opportunity to evaluate if you're drinking too much or too little. Minimizing weight changes during exercise will also minimize the chances of dehydration, as well as hyponatremia from over hydration.

What else can be done to prevent hyponatremia?

Consuming salt tablets during exercise will increase sodium intake and help combat hyponatremia. Additionally, consuming GU or Roctane gels during exercise can also help prevent hyponatremia. GU contains approximately 50 milligrams of sodium, while Roctane contains approximately 125 milligrams (about half as much sodium as 500 millilitres of the average sports drink). Because that sodium is not in a large volume, it can help prevent dilution of blood sodium from drink consumption during exercise.

What if you are one of the many athletes who lose weight from dehydration during exercise?

Join the club! Maximal sweat rates exceed maximal rates of fluid absorption by the gut, and most athletes do not consume enough fluids to maximize gut fluid absorption. Most athletes cannot consume enough fluid during exercise to match rates of loss, which has been well documented. Therefore, pre-hydration before exercise can help athletes start the event in a hydrated state. Athletes who lose weight during exercise should try and minimize those losses by increasing the volume of ingested fluids during exercise to what is tolerable by their gastro-intestinal track. For every pound lost, approximately 500 ml of additional fluid needs to be ingested.

For athletes who lose weight during exercise, thirst may not always be the best indicator of hydration status. Therefore, it is important to drink before you are thirsty to help minimize loss of body weight from dehydration during exercise.

Full Disclosure: GU Energy is a paying sponsor of certain IRONMAN® events and/or an advertiser on certain IRONMAN® media properties. The foregoing article has been prepared and published here as promotional consideration under an agreement regarding such sponsorship and/or advertisement.


Bryan Bergman, PhD, is an associate professor of medicine and a member of the Scientific Advisory Board for GU Energy Labs. Brent Mann, MS, is VP of R&D/Scientific Affairs for GU Energy Labs.