title: Hyponatremia in a cold weather ultraendurance race.
abstract: We assessed the incidence and etiology of hyponatremia in the 100-mile (161 km) Iditasport ultramarathon. Subjects (8 cyclists, 8 runners) were weighed and serum sodium was measured pre- and post-race. Race diets were analyzed to determine fluid and sodium consumption. Subjects were split by post-race serum sodium concentration into hyponatremic and normonatremic groups for statistical analyses. Seven of 16 subjects (44%) were hyponatremic. The hyponatremic group exhibited a significant decrease in serum sodium concentration (137.0 to 132.9 mmol/L), and the normonatremic group experienced a significant decrease in weight (82.1 to 80.2 kg) pre- to post-race. The hyponatremic group drank more fluid per hour (0.5 versus 0.4 L/h) and consumed less sodium per hour (235 versus 298 mg/h) compared to the normonatremic group. In conclusion, hyponatremia is common in an ultraendurance race held in the extreme cold, and may be caused by excessive fluid consumption and/or inadequate sodium intake.
authors.affiliation: Health and Exercise Sciences Department, Campus Box 432, Gettysburg College, Gettysburg, PA 17325, USA. kstuempf@gettysburg.edu
authors.forename: Kristin J
authors.initials: KJ
authors.lastname: Stuempfle
authors.forename: Donald R
authors.initials: DR
authors.lastname: Lehmann
authors.forename: H Samuel
authors.initials: HS
authors.lastname: Case
authors.forename: Stephen
authors.initials: S
authors.lastname: Bailey
authors.forename: Sherri Lind
authors.initials: SL
authors.lastname: Hughes
authors.forename: Jennifer
authors.initials: J
authors.lastname: McKenzie
authors.forename: Deborah
authors.initials: D
authors.lastname: Evans
mesh_terms: D000328:Adult; D000413:Alaska / Q000453:epidemiology; D001642:Bicycling / Q000502:physiology*; D003080:Cold Temperature / Q000009:adverse effects*; D004326:Drinking; D005260:Female; D006801:Humans; D007010:Hyponatremia / Q000453:epidemiology / Q000209:etiology*; D015994:Incidence; D008297:Male; D010807:Physical Endurance / Q000502:physiology*; D012420:Running / Q000502:physiology*; D012964:Sodium / Q000008:administration & dosage / Q000097:blood; D014882:Water-Electrolyte Balance
chemical_list: D012964:Sodium