First reported cases of exercise-associated hyponatremia in Asia

Area of Science:

• Sports Medicine
• Environmental Physiology
• Endurance Sports

Background:

• Exercise-associated hyponatremia (EAH) is a condition linked to prolonged physical activity, particularly in warm environments.
• While EAH is documented globally, there are no prior reports from tropical Asia.
• Understanding fluid balance and EAH incidence in tropical endurance events is crucial for athlete safety.

Purpose of the Study:

• To determine the incidence of EAH in runners seeking medical attention during long-distance races in a tropical climate.
• To assess fluid balance, indicated by body mass changes, in marathon and ultra-marathon runners in a warm and humid environment.

Main Methods:

• Prospective study conducted during 42-km marathon and 84-km ultra-marathon events in a tropical environment (mean temperature 29.0°C, 89% humidity).
• Body mass was measured pre- and post-race to calculate body mass change (% ΔBM).
• Blood sodium concentration was measured for symptomatic runners presenting to the on-site medical tent.

Main Results:

• Three of eight symptomatic runners admitted to the medical tent were diagnosed with EAH (sodium levels 134, 131, and 117 mmol/L).
• Significant body mass gain (indicative of overhydration) was observed in 7% of 42-km runners and 8% of 84-km runners.
• Mean % ΔBM was -1.6% for the marathon and -2.3% for the ultra-marathon, with individual weight gain up to 1.4%.

Conclusions:

• EAH occurs in endurance races held in tropical Asia, challenging previous assumptions of its absence.
• The prevalence of weight gain among runners suggests a risk of excessive fluid intake, contributing to EAH.
• Dissemination of EAH prevention and treatment guidelines is essential for athletes and medical staff in tropical race settings.