Runners At Risk for Hyponatremia from Over-hydration

Nearly half of recreational runners may be drinking too much fluid during races.

If you run—whether a morning two-miler or a half or full marathon—you’ve heard the advice that you need to drink plenty of fluids, especially during races, time and time again.

But it turns out that advice may not be true and could actually endanger your health, rather than keeping you safe. According to a study published recently in the British Journal of Sports Medicine, nearly half of recreational runners may be drinking too much fluid during races, according to a survey of runners by Loyola University Health System researchers.

Expert guidelines recommend runners drink only when thirsty. But a survey of runners by Loyola researchers found that 36.5% percent of runners drink according to a preset schedule or to maintain a certain body weight and 8.9% drink as much as possible. But the danger of this approach is that over-consumption of fluids can lead to exercise-associated hyponatremia (EAH).

“Runners at highest risk of EAH exhibit behavior that is shaped by their beliefs about the benefits and risks of hydration. These beliefs are frequently based on misconceptions about basic exercise physiology,” the Loyola researchers wrote in the study abstract.

Other results of the survey showed that 29.6% of runners incorrectly believed they needed to ingest extra salt while running. And more than half (57.6%) said they drink sports drinks because they have electrolytes that prevent low blood sodium.

But the catch is that the main cause of low sodium in runners is drinking too much water or sports drinks.

The key to preventing overconsumption of fluids is to drink only when thirsty. “It’s the safest known way to hydrate during endurance exercise,” James Winger, MD, a Loyola sports medicine specialist and first author of the study, said in a statement. In addition, the International Marathon Medical Directors Association recommends that runners drink only when thirsty.

Over the last few years, there have been 12 documented and eight suspected deaths from EAH in runners, said Loyola exercise physiologist Lara Dugas, PhD, a study co-author.

For the study, the researchers surveyed 197 runners who competed in the 2009 Westchester, Ill., Veterans Day 10K and 5K runs and two other runs in Chicago. The 91 male runners, on average, had been running for 13 years and had run an average of 1.9 10K races and 0.9 marathons. The 106 women, on average, had been running 8.3 years and had run an average of 1.3 10K races and 0.7 marathons.

The runners generally said advertising by sports drink manufacturers had little or no influence on their beliefs, but the behavior of many of them indicated otherwise.

During the 1980s and 1990s, sports drinks ads warned about the supposed dangers of dehydration and recommended that runners consume as much as five cups of fluids per hour. The erroneous belief that runners should drink as much as they can or according to a preset schedule persists.

“We have been trained to believe that dehydration is a complication of endurance exercise,” Dugas said in the statement. “But, in fact, the normal physiological response to exercise is to lose a small amount of fluid. Runners should expect to lose several pounds during runs, and not be alarmed.”

SourcesNearly Half of Runners May Be Drinking Too Much During Races [Loyola University Health System]Beliefs about Hydration and Physiology Drive Drinking Behaviours in Runners [British Journal of Sports Medicine]