title: Oral salt supplementation during ultradistance exercise.
abstract: OBJECTIVE
  The objective of this study was to determine whether sodium supplementation 1) influences changes in body weight, serum sodium [Na], and plasma volume (PV), and 2) prevents hyponatremia in Ironman triathletes.
  
  
  METHODS
  The study was carried out at the South African Ironman triathlon.
  
  
  METHODS
  Thirty-eight athletes competing in the triathlon were given salt tablets to ingest during the race. Data collected from these athletes [salt intake group (SI)] were compared with data from athletes not given salt [no salt group (NS)].
  
  
  METHODS
  Salt tablets were given to the SI group to provide approximately 700 mg/h of sodium.
  
  
  METHODS
  Serum sodium, hemoglobin, and hematocrit were measured at race registration and after the race. Weights were measured before and after the race. Members of SI were retrospectively matched to subjects in NS for 1) weight change and 2) pre-race [Na].
  
  
  RESULTS
  The SI group developed a 3.3-kg weight loss (p < 0.0001) and significantly increased their [Na] (delta[Na] 1.52 mmol/L; p = 0.005). When matched for weight change during the race, SI increased their [Na] compared with NS (mean 1.52 versus 0.04 mmol/L), but this did not reach statistical significance (p = 0.08). When matched for pre-race [Na], SI had a significantly smaller percent body weight loss than NS (-4.3% versus -5.1%; p = 0.04). There was no significant difference in the increase of [Na] in both groups (1.57 versus 0.84 mmol/L). PV increased equally in both groups. None of the subjects finished the race with [Na] < 135 mmol/L.
  
  
  CONCLUSIONS
  Sodium ingestion was associated with a decrease in the extent of weight loss during the race. There was no evidence that sodium ingestion significantly influenced changes in [Na] or PV more than fluid replacement alone in the Ironman triathletes in this study. Sodium supplementation was not necessary to prevent the development of hyponatremia in these athletes who lost weight, indicating that they had only partially replaced their fluid and other losses during the Ironman triathlon.
authors.affiliation: Department of General Practice and Primary Care, University of Auckland, New Zealand. dalespeedy@e3.net.nz
authors.forename: Dale B
authors.initials: DB
authors.lastname: Speedy
authors.forename: John M D
authors.initials: JM
authors.lastname: Thompson
authors.forename: Ian
authors.initials: I
authors.lastname: Rodgers
authors.forename: Malcolm
authors.initials: M
authors.lastname: Collins
authors.forename: Karen
authors.initials: K
authors.lastname: Sharwood
authors.forename: Timothy D
authors.initials: TD
authors.lastname: Noakes
mesh_terms: D000284:Administration, Oral; D000328:Adult; D001265:Athletic Injuries / Q000209:etiology / Q000378:metabolism / Q000517:prevention & control*; D001642:Bicycling / Q000293:injuries* / Q000502:physiology; D001835:Body Weight / Q000187:drug effects; D019587:Dietary Supplements; D004327:Drinking Behavior; D006400:Hematocrit; D006454:Hemoglobins / Q000032:analysis / Q000187:drug effects; D006801:Humans; D007010:Hyponatremia / Q000209:etiology / Q000378:metabolism / Q000517:prevention & control*; D008297:Male; D010953:Plasma Volume / Q000187:drug effects; D012420:Running / Q000293:injuries* / Q000502:physiology; D012964:Sodium / Q000097:blood; D017673:Sodium Chloride, Dietary / Q000008:administration & dosage* / Q000494:pharmacology; D013550:Swimming / Q000293:injuries* / Q000502:physiology
chemical_list: D006454:Hemoglobins; D017673:Sodium Chloride, Dietary; D012964:Sodium