How does hyponatremia affect athletes and marathon runners and how can it be avoided?

Updated: Jun 17, 2019
  • Author: Eric E Simon, MD; Chief Editor: Vecihi Batuman, MD, FASN  more...
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Acute hyponatremia is associated with ultra-endurance athletes and marathon runners. [26] With women making up a higher percentage, the strongest single predictor is weight gain during the race correlating with excessive fluid intake. Longer racing time and body mass index extremes are also associated with hyponatremia, whereas the composition of fluids consumed (plain water rather than sports drinks containing electrolytes) is not. Oxidization of glycogen and triglyceride during a race is associated with the production of "bound" water, which then becomes an endogenous, electrolyte-free water infusion contributing to hyponatremia induced by water ingestion in excess of water losses.

It should be noted that some collapsed runners are normonatremic or even hypernatremic, [27] making blanket recommendations difficult. However, fluid intake to the point of weight gain should be avoided. [27, 28] Athletes should rely on thirst as their guide for fluid replacement and avoid fixed, global recommendations for water intake. Symptomatic hyponatremic patients should receive 100 mL of 3% sodium chloride over 10 minutes in the field before transportation to hospital. This maneuver should raise the plasma sodium concentration an average of 2-3 mEq/L. [29]

Nonsteroidal anti-inflammatory drug (NSAID) use may increase the risk of development of hyponatremia by strenuous exercise by inhibiting prostaglandin formation. Prostaglandins have a natriuretic effect. Prostaglandin depletion increases NaCl reabsorption in the thick ascending limb of Henle (ultimately increasing medullary tonicity) and ADH action in the collecting duct, leading to impaired free water excretion. [30]

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