title: Hyponatremia is associated with higher NT-proBNP than normonatremia after prolonged exercise.
abstract: OBJECTIVE
  To determine the incidence of and risk factors for exercise-associated hyponatremia (EAH) in cyclists completing a long-distance bike ride and to assess whether postexercise serum NT-proBNP concentration (brain natriuretic protein precursor) differed between riders with and without EAH.
  
  
  METHODS
  Observational study.
  
  
  METHODS
  "Around the Bay in a Day" cycle event, October 2010.
  
  
  METHODS
  One hundred thirty-nine cyclists prospectively enrolled, with 90 completing 210 or 250 km.
  
  
  METHODS
  Body weight change and fluid intake during the event, and postevent serum sodium concentration ([Na+]) and NT-proBNP concentration ([NT-proBNP]).
  
  
  RESULTS
  Four riders (4.5%) were hyponatremic ([Na+] < 135 mmol/L). The lowest postride [Na+] was 126 mmol/L. Hyponatremia was associated with a mean weight gain of 3.4 kg (3.9% of total body weight). Significant negative correlations were found between postride [Na+] and change in weight (r = -0.34; P < 0.01) and fluid intake when expressed as total volume (r = -0.35; P < 0.01), mL/kg body weight (r = 0.33; P < 0.01), mL·kg·h (r = -0.27; P < 0.01), or mL/h (r = -0.29; P < 0.01). NT-proBNP concentrations levels in 3 of the 4 hyponatremic subjects were markedly elevated compared with eunatremic subjects matched for age, sex, distance ridden, training, and medical history.
  
  
  CONCLUSIONS
  Exercise-associated hyponatremia was found to occur in 4.5% of the study group and was associated with weight gain during a prolonged bike ride. Postride [Na+] varied inversely with weight change and with fluid intake. Three of 4 hyponatremic riders had significant elevations of [NT-proBNP]. These results support the hypothesis that overconsumption of hypotonic fluids in this setting is the most important cause of EAH.
authors.affiliation: MP Sports Physicians, Victoria, Australia. drgaharris@yahoo.com
authors.forename: Gregory
authors.initials: G
authors.lastname: Harris
authors.forename: Stephen
authors.initials: S
authors.lastname: Reid
authors.forename: Ken
authors.initials: K
authors.lastname: Sikaris
authors.forename: Paul
authors.initials: P
authors.lastname: McCrory
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001642:Bicycling / Q000502:physiology*; D004326:Drinking / Q000502:physiology; D005260:Female; D006801:Humans; D007010:Hyponatremia / Q000097:blood* / Q000503:physiopathology*; D015994:Incidence; D008297:Male; D008875:Middle Aged; D020098:Natriuretic Peptide, C-Type / Q000097:blood*; D011446:Prospective Studies; D012307:Risk Factors; D012964:Sodium / Q000097:blood*; D015430:Weight Gain / Q000502:physiology; D055815:Young Adult
chemical_list: C480579:amino-terminal pro-C-type natriuretic peptide, human; D020098:Natriuretic Peptide, C-Type; D012964:Sodium