Oral Salt Supplementation During Ultradistance Exercise

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. Setting The study was carried out at the South African Ironman triathlon. Participants 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). Interventions Salt tablets were given to the SI group to provide approximately 700 mg/h of sodium. Main Outcome Measurements 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 (ΔNa 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.