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Hyponatremia in ultradistance triathletes
D B Speedy1, T D Noakes, I R Rogers
1Sportsmed, Christchurch, New Zealand. dale.speedy@xtra.co.nz
Medicine and Science in Sports and Exercise
|June 23, 1999
Summary
Hyponatremia, or low plasma sodium, is common in ultraendurance triathletes but often asymptomatic. Severe cases are frequently caused by fluid overload, particularly in athletes who maintain or gain weight during the race.
Area of Science:
- Sports Medicine
- Exercise Physiology
- Biochemistry
Background:
- Hyponatremia (plasma sodium <135 mmol x L(-1)) is a recognized risk in ultraendurance events.
- The exact causes of hyponatremia in these athletes remain unclear.
Purpose of the Study:
- To prospectively investigate the incidence and causes of hyponatremia in an ultradistance triathlon.
- To identify factors associated with hyponatremia in endurance athletes.
Main Methods:
- Observational cohort study of 605 athletes in the New Zealand Ironman triathlon.
- Collected pre- and post-race weights and post-race plasma sodium concentrations from 330 finishers.
Main Results:
- 18% (58/330) of finishers had hyponatremia; most cases were asymptomatic.
- Severe hyponatremia (<130 mmol x L(-1)) was linked to weight maintenance or gain (fluid overload) in 73% of affected athletes.
- Women had lower plasma sodium concentrations and less relative weight loss than men.
Conclusions:
- Hyponatremia is a prevalent biochemical finding in ultradistance triathletes.
- Fluid overload is a primary cause of severe, symptomatic hyponatremia.
- Understanding these factors is crucial for athlete safety and performance.