GLOSSARY

Exercise-associated hyponatraemia, or EAH, is a fall in blood sodium below 135 mmol/L during exercise or up to 24 hours afterwards. It occurs in marathons, ultramarathons, triathlons and long hikes and can be fatal in severe cases.

Main Cause

The main cause is drinking too much water or low-sodium drinks relative to water lost, together with non-osmotic ADH release, which impairs the kidney’s excretion of the extra water. Sodium loss in sweat plays a contributing role but is not the main cause on its own.

Risk Factors

Weight gain during the race, long duration (more than 4 hours), slow pace (slower runners have more chance to drink), low body weight, female sex, many drink stations and NSAID use.

Symptoms

• Mild: nausea, bloating, headache and swollen hands and feet (a tight ring).
• Severe (EAH with encephalopathy): vomiting, confusion, seizures and coma because of brain swelling; also pulmonary oedema.

Treatment