title: The need for salt: does a relationship exist between cystic fibrosis and exercise-associated hyponatremia?
abstract: Salt replacement is often recommended to prevent exercise-associated hyponatremia (EAH) despite a lack of evidence to support such practice. Exercise-associated hyponatremia is known to be a complex process resulting from the interplay of hydration, arginine vasopressin, and sodium balance. Although evidence suggests overhydration is the dominant pathophysiologic factor in most cases, the contributions of sweat sodium losses remain unclear. A theoretical genetic mechanism producing exuberant sweat sodium loss in athletes is the presence of cystic fibrosis (CF) gene. Individuals with CF develop hypovolemic hyponatremia by sodium loss via sweat through a defective chloride ion transport channel, the CF transmembrane conductance regulator (CFTR). Elevated sweat sodium concentrations in CF single heterozygotes suggest that athletes developing EAH may be CFTR carriers. We targeted the 2010 and 2011 Western States Endurance Run ultramarathon, an event where athletes with EAH regularly present in a hypovolemic state, for a cohort maximizing the potential to document such a relationship. A total of 798 runners started the 2010 (n = 423) and 2011 (n = 375) races. Of the 638 finishers, 373 were screened for EAH by blood draw, 60 (16%) were found to have EAH, and 31 (alpha = 0.05 for n = 9) reported their CF result from a saliva-based genetic testing kit. Neither the 31 EAH-positive athletes nor the 25 EAH-negative comparison cohort athletes tested positive for a CF mutation. This null relationship suggests that CFTR mutations are not associated with the development of EAH and that salt supplementation is unnecessary for such a reason.
authors.affiliation: 1Department of Family and Maternal/Child, Via Christi Family Medicine Residency, Via Christi Health System, Wichita, Kansas; 2Department of Physical Medicine and Rehabilitation, VA Northern California Health Care System and University of California Davis Medical Center, Sacramento, California; 3Department of Health Sciences, Gettysburg College, Gettysburg, Pennsylvania; 4Sir Charles Gairdner Hospital, Perth, Australia; 5Department of Emergency Medicine, St John of God Murdoch Hospital and University of Notre Dame, Murdoch, Western Australia; 6Division of Endocrinology and Metabolism, Georgetown University Medical Center, Washington, District of Columbia; and 7School of Health Science, Oakland University, Rochester, Michigan.
authors.forename: Douglas P
authors.initials: DP
authors.lastname: Lewis
authors.forename: Martin D
authors.initials: MD
authors.lastname: Hoffman
authors.forename: Kristin J
authors.initials: KJ
authors.lastname: Stuempfle
authors.forename: Bethan E
authors.initials: BE
authors.lastname: Owen
authors.forename: Ian R
authors.initials: IR
authors.lastname: Rogers
authors.forename: Joseph G
authors.initials: JG
authors.lastname: Verbalis
authors.forename: Tamara D
authors.initials: TD
authors.lastname: Hew-Butler
mesh_terms: D001835:Body Weight; D016022:Case-Control Studies; D003550:Cystic Fibrosis / Q000150:complications / Q000235:genetics*; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000235:genetics*; D005260:Female; D005820:Genetic Testing; D006579:Heterozygote; D006801:Humans; D007010:Hyponatremia / Q000175:diagnosis / Q000235:genetics* / Q000517:prevention & control; D008297:Male; D012420:Running / Q000502:physiology*; D012964:Sodium / Q000008:administration & dosage / Q000097:blood*; D013542:Sweat / Q000737:chemistry / Q000378:metabolism; D013546:Sweating
chemical_list: C505032:CFTR protein, human; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D012964:Sodium