Hyponatremia and Ultramarathons

John V. Anderson, MRCP; Virend K. Somers, MB, ChB; James Conway, FRCP; Stephen R. Bloom, FRCP; Peter Sleight, FRCP
JAMA. 1986;256(2):213-214. doi:10.1001/jama.1986.03380020075016.
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To the Editor.—  Marathon running is gaining increasing popularity. An understanding of the pathophysiology of exertion is important so that runners can be advised on how to minimize the medical hazards of their sport. We therefore read with great interest the report by Frizzell et al1 describing severe acute hyponatremia in marathon runners. The authors attribute the hyponatremia detected in their patients to an excessive loss of sodium in sweat and to drinking hypotonic fluids. Undoubtedly these are important etiologic factors.The recent discovery of a putative natriuretic hormone,2 atrial natriuretic peptide (ANP), is causing a major revision in the understanding of salt and water homeostasis. Increasing the circulating concentration of ANP has been shown to cause a salt-losing state in man.3 There are to date no published data on the effects of exertion on circulating concentrations of ANP. We have therefore performed a pilot study to


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