With the peak of summer just around the corner, questions about proper hydration for athletes inevitably arise. But can hydration during exercise go too far?

In the Statement of the Third International Exercise-Associated Hyponatremia Consensus Development Conference, published in the Journal of Clinical Sport Medicine in July, a group of experts sought to address a condition known as exercise-associated hyponatremia.

Hyponatremia, defined as sodium levels lower than 135 mmol/L, developing during or 24 hours after exercise is referred to as exercise-associated hyponatremia (EAH).1


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“This is the most extreme form of an acute hyponatremia. We define acute hyponatremia as something that occurs in less than 48 hours. This occurs typically during the course of a 4- to 5- to 6-hour event. It is the most severe form of acute hyponatremia that I know of, so the treatment parameters are relevant to all forms of acute hyponatremia,” Joseph Verbalis, MD, chief of endocrinology and metabolism at Georgetown University, told Endocrinology Advisor in an interview.

Characteristics of Exercise-Associated Hyponatremia

According to evidence included in the published consensus statement, the incidence of symptomatic EAH has been reported to be as high as 38% and 23% of athletes seeking medical care in an ultramarathon and an Ironman triathlon, respectively. Likewise, cases have been reported after marathons and military training as well.1 

However, EAH is not limited to endurance athletes. Symptomatic EAH has been reported in a range of activities, including hiking, half-marathons, professional and college football, and biking. Additionally, some studies show that low-intensity exercise at high temperatures has induced symptomatic EAH.1

In most cases, hyponatremia develops as a result of a relative excess of total body water, although loss of potassium or sodium may be contributing factors. 

“… Exercise-associated hyponatremia (EAH) is largely an acute, dilutional, hyponatremia from exercise-induced non-osmotic stimulation of arginine vasopressin (AVP). The best preventative strategy is to advise people to drink according to physiologically regulated individualized thirst during exercise. EAH is more about water overload and not about inadequate sodium intake, with sports drinks actually containing very little sodium,” consensus panel member Tamara Hew-Butler, DPM, PhD, of the University of Oakland in Rochester, Michigan, said in an email interview with Endocrinology Advisor.

The severity of symptoms depends on how quickly sodium drops and the level to which sodium drops from baseline. Therefore, symptoms can rapidly develop even with modest hyponatremia (125 mmol/L to 130 mmol/L).

Pooled data indicate that only 0.8% of individuals begin a race with hyponatremia; therefore, it is generally believed that EAH typically develops during or post-exercise.1

Asymptomatic EAH is typically found in athletes who were tested for research purposes, but symptomatic EAH may range in presentation from mild nausea or lightheadedness to confusion, seizures, vomiting or headaches.

One particularly notable life-threatening complication of EAH is exercise-associated hyponatremic encephalopathy (EAHE) secondary to cerebral edema.

Risk factors for the development of EAH include duration of exercise of more than 4 hours, slower pace, inexperience, inadequate training and overconsumption of water or hypotonic beverages. EAH is also associated with a higher or lower BMI and weight gain during exercise.