Exercise-associated hyponatremia

Exercise-associated hyponatremia (EAH) is a condition characterized by an abnormally low concentration of sodium in the blood that occurs during or up to 24 hours after physical exercise. EAH is defined by a serum sodium concentration below 135 mmol/L and is considered severe when levels drop below 125 mmol/L. This condition is of particular concern in endurance sports and activities, such as marathons, triathlons, and ultramarathons, where it has been most frequently documented.

Causes and Risk Factors

The primary cause of EAH is the excessive intake of fluids, particularly water, which dilutes the sodium concentration in the blood. This is often compounded by the loss of sodium through sweat during prolonged physical activity. Factors that increase the risk of developing EAH include duration and intensity of exercise, high or low environmental temperatures, nonsteroidal anti-inflammatory drug (NSAID) use, and the individual's sweat sodium concentration. Female athletes and those with a lower body weight or body mass index (BMI) are also at a higher risk.

Symptoms

Symptoms of EAH can range from mild and nonspecific to severe and life-threatening. Mild symptoms include nausea, bloating, puffiness, and headache. As the condition progresses, more severe symptoms such as confusion, seizures, respiratory distress, and altered mental status can occur. In extreme cases, EAH can lead to cerebral edema, non-cardiogenic pulmonary edema, coma, and death.

Prevention and Treatment

Prevention of EAH focuses on educating athletes about the risks of overhydration and advising them to drink according to thirst rather than consuming large volumes of fluid preemptively. Monitoring body weight before and after exercise can also help assess fluid balance. Sports drinks containing electrolytes, particularly sodium, can be beneficial for individuals participating in prolonged or intense exercise.

Treatment of EAH depends on the severity of the condition. Mild cases may only require restriction of fluid intake and close monitoring. More severe cases necessitate medical intervention, which can include the administration of hypertonic saline solution to rapidly increase serum sodium levels. It is crucial for the treatment to be carefully managed to avoid rapid overcorrection, which can lead to osmotic demyelination syndrome, a serious neurological condition.

Epidemiology

The incidence of EAH varies widely among different sports and events, with higher rates observed in endurance events. Surveys and studies have reported incidence rates ranging from 0% to over 10% in marathon runners, with similar or slightly lower rates in other endurance athletes.

Conclusion

Exercise-associated hyponatremia is a potentially serious condition that can be prevented through proper hydration strategies and awareness of the symptoms. Athletes, coaches, and medical personnel should be educated on the risks of overhydration and the importance of monitoring fluid intake during prolonged physical activity.