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Water Overload: On the Lookout for Hyponatremia

By Monique Ryan

waterTraining and racing in hot and humid weather can really drive the thirst mechanism and conjure up images of grueling workouts and hitting your fluids and electrolytes. Hitting just the right amount is crucial to preventing the sometimes fatal condition known as exertional hyponatremia, or low blood sodium, that too often occurs during longer competitive efforts.

“Hyponatremia is an example of how too much of a good thing, water, can become a bad thing,” said Bob Murray, Ph.D., of Sports Science Insights. While most marathoners are likely to finish the race in the dehydrated state, the risk of suffering from exertional hyponatremia during the race is higher than many triathletes may realize.

“Overhydration, especially with water, but even with sports drinks, is the main cause of hyponatremia,” said Registered Dietitian Christine Gerbstedt. “There is a small subset of athletes who will be more susceptible to this condition due to their unique kidney function, but we can’t predict who these individuals are.”

Hyponatremia is more commonly seen in younger female athletes, especially runners, in races that take over four hours to complete and during a first competition. Exertional hyponatremia is preventable by gathering data during training that allows the triathlete to develop a personalized hydration plan for the long runs and the race.

“Staying well hydrated during training and competition means drinking enough to minimize weight loss and avoiding weight gain,” Murray said. Step on a scale right before and after a workout in various weather training conditions, and keep track of how much fluid you have consumed.

“Weight loss after a run indicates dehydration and the need to drink more, while weight gain indicates overdrinking and the need to reduce fluid intake during training,” Murray said. Each pound of weight loss is 16 ounces of sweat that you did not replace.

Calculate your hourly sweat rate. For example, if you are down one pound after a one hour run during which you consumed 20 ounces of fluid, your total sweat loss during that run was 36 ounces. You can use this information to consume the optimal amounts of fluid per hour, and not overhydrate.

Every runner has their own unique sweat rate at a given temperature. “Ahead of time, new triathletes can speak with sports dietitians, to learn about proper hydration and electrolyte replacement especially focused on the temperature conditions of the upcoming race,” Gerbstadt said.

Sodium is a key electrolyte lost in sweat. Some triathletes may even be “salty sweaters” who are distinguished by the white streaks of salt residue seen on their training clothes after a tough workout. Sports drinks contain sodium and higher sodium sports drinks are often on the race course. Because of the length and fuel demand of the race, carbohydrate replacement is also key as body fuel stores run low.

“A sports drink is the most effective, cheapest and easiest way to improve performance by replacing fluid, sodium and carbohydrate during training and competition,” Murray said.

“Be aware of symptoms of early hyponatremia, like dizziness and confusion,” Gerbstadt said. Other signs include a bloated stomach, fingers, toes, wrists and ankles. “If there is any question, a trip to the medical tent or hospital can save a life. There will always be another race.”

sports nutritionMonique Ryan, MS, RD, CSSD, LDN is a leading endurance sports nutritionist. Her nearly 30 years of professional experience working with Olympic (consultant to USA Triathlon and USA Cycling), elite and age-group endurance athletes and professional sports teams make her one of the most experienced and qualified sports nutritionists in the U.S. Ryan is founder of Chicago-based Personal Nutrition Designs LLC and the best-selling author of “Sports Nutrition for Endurance Athletes” (3rd edition, VeloPress) and three other sports nutrition books. PND LLC provides detailed nutrition plans for triathletes across North America competing in all race distances with programs at Ryan is a licensed dietitian and a certified specialist in sports dietetics.

The views expressed in this article are the opinion of the author and not necessarily the practices of USA Triathlon. Before starting any new diet or exercise program, you should check with your physician and/or coach.