Zielstellung: Untersuchung ob Natrium-Supplementierung bei Ironman-Triathleten 1. Veränderungen im Körpergewicht, Serum-Na und Plasmavolumen (PV) beeinflusst und 2. Hyponatriämie vorbeugt. Probanden/Methoden: Probanden waren 38 Teilnehmer des Ironman-Triathlon in Südafrika (SI). Ihnen wurden während des Wettkampfs Salztabletten (700 mg/h Natrium) verabreicht. Die Daten wurden mit denen von Teilnehmer, die keine Salztabletten bekamen, verglichen (NS, n=133). Gemessen wurden bei Wettkampfanmeldung und nach dem Wettkampf Serum-Na, Hämoglobin, Hämatokrit. Ergebnisse: Die Natriumaufnahme war mit einem Abfall der Höhe des Gewichtsverlustes während des Wettkampfes verbunden. Nicht nachgewiesen konnte, dass Natriumaufnahme signifikant die Veränderungen von Na oder PV mehr als nur Flüssigkeitsersatz beeinflusst. Eine Natriumsupplementierung war zur Vorbeugung von Hyponatriämie bei Teilnehmern mit Gewichtsverlust nicht notwendig. 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] (?[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.
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