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Clin J Sport Med. 2008 Jul;18(4):344-9. doi: 10.1097/JSM.0b013e31817e3515.

Hyponatremia among runners in the Zurich Marathon.

Author information

1
Department of Agricultural and Food Sciences, ETH Zurich, Zurich, Switzerland. samuel.mettler@inw.agrl.ethz.ch

Abstract

OBJECTIVE:

Hyperhydration and exercise-associated hyponatremia (EAH) are critical issues during endurance events. We studied a cohort of marathon runners to examine EAH's prevalence in a marathon with a short time limit and to investigate underlying mechanisms that may be responsible for its development.

DESIGN:

Observational cohort study.

SETTING:

2006 Zurich Marathon (cool and rainy weather, time limit of 5 hours).

PARTICIPANTS:

167 marathon runners were recruited the month before the race.

MAIN OUTCOME MEASURES:

Body mass, plasma sodium, and osmolality were measured just before the start and immediately after the race. Fluid intake during the race was ascertained by a recall questionnaire.

RESULTS:

Five subjects (3 %) developed asymptomatic EAH, and no symptomatic EAH was found. Body mass change during the race correlated similarly with postrace sodium levels (r = -0.72, P < 0.0001) and with sodium change during the race (r = -0.66, P < 0.0001). Postrace sodium levels correlated significantly with sodium change during the race (r = 0.74, P < 0.0001). Fluid intake correlated significantly (r = -0.43, P < 0.0001) with plasma sodium change between the start and finish of the race. Postrace sodium levels and postrace osmolality were significantly correlated (r = 0.68, P < 0.0001).

CONCLUSION:

In this study we observed a relatively low incidence of EAH in subjects running the marathon in around 2.5 to 5 hours and in a cool environment. Plasma sodium change during the race and postrace sodium levels correlated with body mass change. There was also a direct correlation between fluid intake and plasma sodium change during the race.

PMID:
18614886
DOI:
10.1097/JSM.0b013e31817e3515
[Indexed for MEDLINE]

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