No Link between Cystic Fibrosis Mutation and Exercise-associated Hyponatremia

Study of exercise-associated hyponatremia (EAH) in ultramarathon runners finds no relationship between the presence of cystic fibrosis gene and the development of EAH.

Are athletes who carry the genetic mutation for cystic fibrosis (CF) at higher risk of developing exercise-associated hyponatremia (EAH)?

The authors of “The Need for Salt: Does a Relationship Exist Between Cystic Fibrosis and Exercise-Associated Hyponatremia?,” published in The Journal of Strength and Conditioning Research, posited that people who carry a genetic mutation associated with cystic fibrosis may be more prone to develop exercise-associated hyponatremia.

They based this hypothesis in part on the fact that, although evidence suggests “overhydration is the dominant pathophysiologic factor” in most cases of exercise-associated hyponatremia, “the contributions of sweat sodium losses remain unclear.” To prevent the development of exercise-associated hyponatremia, many athletes take salt supplements, despite the lack of solid evidence to support this practice.

Thus, because people with cystic fibrosis tend to develop hypovolemic hyponatremia “by sodium loss via sweat through a defective chloride ion transport channel,” known as the cystic fibrosis transmembrane conductance regulator (CFTR), the authors proposed that elevated sweat sodium concentrations in cystic fibrosis single heterozygotes “suggest” that athletes who develop exercise-associated hyponatremia may be CFTR carriers.

For the study, the authors reviewed data from ultramarathon runners who were screened for exercise-associated hyponatremia (via blood sample testing) and the presence of cystic fibrosis mutation (via saliva-based genetic testing) following the conclusion of a race.

Sixty (16%) of the 373 runners who submitted blood samples were found to have exercise-associated hyponatremia. Thirty-one (31) of these runners were tested for cystic fibrosis mutation. The authors reported that “neither the 31 EAH-positive athletes nor the 25 EAH-negative comparison cohort athletes tested positive for a CF mutation.”

Based on these data, the authors concluded that “CFTR mutations are not associated with the development of EAH and that salt supplementation is unnecessary for such a reason.”