Maintained Serum Sodium in Male Ultra-Marathoners – The Role of Fluid Intake, Vasopressin, and Aldosterone in Fluid and Electrolyte Regulation

Abstract

Exercise-associated hyponatremia (EAH) is a well know electrolyte disorder in endurance athletes. Although fluid overload is the most like etiology, recent studies, however, argued whether EAH is a disorder of vasopressin secretion. The aims of the present study were to investigate (i) the prevalence of EAH in male ultra-marathoners and (ii) whether fluid intake, aldosterone or vasopressin, as measured by copeptin, were associated with post-race serum sodium concentration ([Na⁺]). In 50 male ultra-marathoners in a 100 km ultra-marathon, serum [Na⁺], aldosterone, copeptin, serum and urine osmolality, and body mass were measured pre- and post-race. Fluid intake, renal function parameters and urine excretion were measured. No athlete developed EAH. Copeptin and aldosterone increased; a significant correlation was found between the change in copeptin and the change in serum [Na⁺], no correlation was found between aldosterone and serum [Na⁺]. Serum [Na⁺] increased by 1.6%; body mass decreased by 1.9 kg. The change in serum [Na⁺] and body mass correlated significantly and negatively. The fluid intake of ~ 0.58 l/h was positively related to the change in body mass and negatively to both post-race serum [Na⁺] and the change in serum [Na⁺]. We conclude that serum [Na⁺] was maintained by both the mechanisms of fluid intake and the hormonal regulation of vasopressin.

Key words

electrolytes - aldosterone - vasopressin - ultra-endurance

• References

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