Preventing Exercise-Associated Hyponatremia


Pharmacists have an opportunity to provide patient education regarding proper hydration before exercise.

I was recently listening to a national sports talk radio program and heard Arthur J. Siegel, MD, discussing exercise-associated hyponatremia (EAH), a potentially deadly hyponatremia that occurs during or up to 24 hours after physical activity due to sustained, excessive fluid intake.

As easily accessible health care providers, pharmacists have an opportunity to provide patient education regarding proper hydration before exercise.

I contacted Dr. Siegel and he graciously agreed to answer the following important questions about EAH.

Q: What is the mechanism of EAH and why it is potentially deadly?

A: When the intake of hypotonic fluids (water or sports drinks) during exercise exceeds losses, acute brain swelling may occur with headache, nausea, confusion, and disorientation.

Runners may continue to drink avidly, thinking that these are symptoms of dehydration, but this causes progression to seizures and coma. Brain injury and death may result from acute cerebral edema unless reversed by emergent treatment with hypertonic (3%) saline.

Q: What are the risk factors of EAH?

A: The main risk factor is avid intake of hypotonic fluids driven by a fear of dehydration.

Q: Which patient population is at highest risk of EAH?

A: Athletes, especially young women, who exercise for more than 3 or 4 hours at low intensity but drink like they are running at the front of the pack.

Q: Nonsteroidal anti-inflammatory drugs (NSAIDs) have been implicated as a risk factor for EAH development. Should patients avoid NSAIDs before extended, vigorous exercise?

A: More than 40% of marathoners report using NSAIDs. The risk for kidney injury is small, but acetaminophen is safer.

Q: The general public frequently sees advertisements for sports drinks and water with electrolytes, and as a result, they are generally more concerned about dehydration than overhydration. What should pharmacists tell their patients who are preparing for an endurance competition or training?

A: Overhydration is more dangerous than dehydration, so drink to thirst! Trust your body to tell you how much to consume.

Test your EAH knowledge with this true or false quiz:

1. EAH occurs in >10% of asymptomatic marathon runners [Boston, London].

2. EAH is overhydration due to net fluid retention during exercise.

3. EAH may be due in part to dysregulation of the stress hormone AVP.

4. EAH is more dangerous than dehydration.

5. Sports drinks do not prevent EAH if fluid intake exceeds net losses [fluid in>fluid out].

6. Salt supplements before and during exercise do not prevent EAH if fluid balance is positive.

7. Stop intake of hypotonic fluids including sports drinks if feeling confused or disoriented.

8. Rehydrate slowly after races until urination resumes.

9. Seizures or coma require emergent IV hypertonic (3%) saline to reverse cerebral edema.

10. EAH could never happen to me!

Dr. Siegel is the director of the Internal Medicine and Primary Care Clinic at McLean Hospital and MGH Internal Medicine Associates in Belmont, Massachusetts. He is an associate professor of medicine at Harvard Medical School and a fellow of the American College of Physicians. As a former marathoner, his research on runners in Boston has contributed to the prevention and emergent treatment of rare yet life-threatening complications, including cerebral edema from water intoxication in young females and cardiac arrest in middle-aged males. He advocates for use of pre-race aspirin to prevent cardiac events in susceptible runners.

Quiz Answers

1-9: True

10: False


  • Hew-Butler T, Rosner, MH, Fowkes-Godek, S, et al. Statement of the Third International Exercise-Associated Hyponatremia Consensus Development Conference, Carlsbad, California, 2015. Clin J Sport Med. 2015;25:303—320.
  • Rosner, MH. Preventing Deaths Due to Exercise-Associated Hyponatremia: The 2015 Consensus Guidelines. Clin J Sport Med. 2015;25:301—302.
  • Siegel AJ. Fatal Water Intoxication and Cardiac Arrest in Runners During Marathons: Prevention and Treatment Based on Validated Clinical Paradigms. Am J Med. 2015;21: S0002-9343(15)00353-8. DOI:
  • Ayus JC, Varon J, Arieff AI. Hyponatremia, cerebral edema, and noncardiogenic pulmonary edema in marathon runners. Ann Intern Med. 2000; 132:711—714.
  • Davis DP, Videen JS, Marino A, et al. Exercise-associated hyponatremia in marathon runners: a two-year experience. J Emerg Med. 2001;21:47—57.
  • Wharam PC, Speedy DB, Noakes TD, et al. NSAID use increases the risk of developing hyponatremia during an Ironman triathlon. Med Sci Sports Exerc. 2006;38:618—622.

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