title: Higher prevalence of exercise-associated hyponatremia in female than in male open-water ultra-endurance swimmers: the 'Marathon-Swim' in Lake Zurich.
abstract: We investigated the prevalence of exercise-associated hyponatremia (EAH) in 25 male and 11 female open-water ultra-endurance swimmers participating in the 'Marathon-Swim' in Lake Zurich, Switzerland, covering a distance of 26.4 km. Changes in body mass, fat mass, skeletal muscle mass, total body water, urine specific gravity, plasma sodium concentration [Na(+)] and haematocrit were determined. Two males (8%) and four females (36%) developed EAH where one female was symptomatic with plasma sodium [Na(+)] of 127 mmol/L. Body mass and plasma [Na(+)] decreased (p < 0.05). The changes in body mass correlated in both male and female swimmers to post-race plasma [Na(+)] (r = -0.67, p = 0.0002 and r = -0.80, p = 0.0034, respectively) and changes in plasma [Na(+)] (r = -0.68, p = 0.0002 and r = -0.79, p = 0.0039, respectively). Fluid intake was neither associated with changes in body mass, post-race plasma [Na(+)] or the change in plasma [Na(+)]. Sodium intake showed no association with either the changes in plasma [Na(+)] or post-race plasma [Na(+)]. We concluded that the prevalence of EAH was greater in female than in male open-water ultra-endurance swimmers.
authors: Institute of General Practice and Health Services Research, University of Zurich, Zurich, Switzerland.
authors: Sandra
authors: S
authors: Wagner
authors: Beat
authors: B
authors: Knechtle
authors: Patrizia
authors: P
authors: Knechtle
authors: Christoph Alexander
authors: CA
authors: Rüst
authors: Thomas
authors: T
authors: Rosemann
mesh_terms: D000328:Adult; D056352:Athletes; D015444:Exercise / Q000502:physiology*; D005260:Female; D006801:Humans; D007010:Hyponatremia / Q000453:epidemiology* / Q000209:etiology*; D060106:Lakes; D008297:Male; D008875:Middle Aged; D010807:Physical Endurance / Q000502:physiology*; D015995:Prevalence; D012420:Running / Q000502:physiology; D012727:Sex Characteristics; D013550:Swimming / Q000502:physiology*; D013557:Switzerland / Q000453:epidemiology; D014867:Water
chemical_list: D014867:Water