title: Low prevalence of exercise-associated hyponatremia in male 100 km ultra-marathon runners in Switzerland.
abstract: We investigated the prevalence of exercise-associated hyponatremia (EAH) in 145 male ultra-marathoners at the '100-km ultra-run' in Biel, Switzerland. Changes in body mass, urinary specific gravity, haemoglobin, haematocrit, plasma [Na(+)], and plasma volume were determined. Seven runners (4.8%) developed asymptomatic EAH. Body mass, haematocrit and haemoglobin decreased, plasma [Na(+)] remained unchanged and plasma volume increased. Δ body mass correlated with both post race plasma [Na(+)] and Δ plasma [Na(+)]. Δ plasma volume was associated with post race plasma [Na(+)]. The athletes consumed 0.65 (0.30) L/h; fluid intake correlated significantly and negatively (r = -0.50, p < 0.0001) to race time. Fluid intake was neither associated with post race plasma [Na(+)] nor with Δ plasma [Na(+)], but was related to Δ body mass. To conclude, the prevalence of EAH was low at ~5% in these male 100 km ultra-marathoners. EAH was asymptomatic and would not have been detected without the measurement of plasma [Na(+)].
authors.affiliation: Facharzt FMH für Allgemeinmedizin, Gesundheitszentrum St. Gallen, Vadianstrasse 26, 9001 St. Gallen, Switzerland. beat.knechtle@hispeed.ch
authors.forename: Beat
authors.initials: B
authors.lastname: Knechtle
authors.forename: Patrizia
authors.initials: P
authors.lastname: Knechtle
authors.forename: Thomas
authors.initials: T
authors.lastname: Rosemann
mesh_terms: D000328:Adult; D056352:Athletes / Q000706:statistics & numerical data*; D001823:Body Composition; D004326:Drinking / Q000502:physiology; D015444:Exercise / Q000502:physiology*; D006801:Humans; D007010:Hyponatremia / Q000453:epidemiology* / Q000209:etiology*; D008297:Male; D008875:Middle Aged; D010807:Physical Endurance; D015995:Prevalence; D012420:Running / Q000706:statistics & numerical data; D013557:Switzerland / Q000453:epidemiology