title: Hyponatremia in the 2009 161-km Western States Endurance Run.
abstract: OBJECTIVE
  To determine the incidence of exercise-associated hyponatremia (EAH), the associated biochemical measurements and risk factors for EAH, and whether there is an association between postrace blood sodium concentration ([Na+]) and changes in body mass among participants in the 2009 Western States Endurance Run, a 161-km mountain trail run.
  
  
  METHODS
  Change in body mass, postrace [Na+], and blood creatine phosphokinase (CPK) concentration, and selected runner characteristics were evaluated among consenting competitors.
  
  
  RESULTS
  Of the 47 study participants, 14 (30%) had EAH as defined by a postrace [Na+] <135 mmol/L. Postrace [Na+] and percent change in body mass were directly related (r = .30, P = .044), and 50% of those with EAH had body mass losses of 3-6%. EAH was unrelated to age, sex, finish time, or use of nonsteroidal anti-inflammatory drugs during the run, but those with EAH had completed a smaller (P = .03) number of 161-km ultramarathons. The relationship of CPK levels to postrace [Na+] did not reach statistical significance (r = -.25, P = .097).
  
  
  CONCLUSIONS
  EAH was common (30%) among finishers of this 161-km ultramarathon and it was not unusual for those with EAH to be dehydrated. As such, changes in body mass should not be relied upon in the assessment for EAH during 161-km ultramarathons.
authors.affiliation: Department of Physical Medicine & Rehabilitation, Department of Veterans Affairs, Northern California Health Care System, Sacramento, CA, USA.
authors.forename: Martin D
authors.initials: MD
authors.lastname: Hoffman
authors.forename: Kristin J
authors.initials: KJ
authors.lastname: Stuempfle
authors.forename: Ian R
authors.initials: IR
authors.lastname: Rogers
authors.forename: Louise B
authors.initials: LB
authors.lastname: Weschler
authors.forename: Tamara
authors.initials: T
authors.lastname: Hew-Butler
mesh_terms: D000328:Adult; D015992:Body Mass Index; D002140:California; D003681:Dehydration / Q000503:physiopathology; D005260:Female; D006358:Hot Temperature; D006801:Humans; D007010:Hyponatremia / Q000453:epidemiology / Q000503:physiopathology*; D015994:Incidence; D008297:Male; D008875:Middle Aged; D010807:Physical Endurance / Q000502:physiology*; D012307:Risk Factors; D012420:Running / Q000502:physiology*