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Exercise-Induced Hyponatremia: Risk for Marathon Runners

  • 6/17/2014 10:23:00 AM
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Exercise-Induced Hyponatremia: Risk for Marathon Runners

Kaleigh Camp, M.S.

Standing at the starting line of the 2011 San Antonio Rock ‘n’ Roll half marathon with over 30,000 other runners, it was clear how popular these races have become for athletes as well as non-athletes. Running USA, the track and field running information center, acknowledges the surge over the past quarter of a century. At the beginning of the race, salt packets were provided and passed around the population of runners.

I wondered whether all runners understand the purpose of these salt packets. The runner standing next to me said she didn’t know. Salt packets help prevent the risk of exercise-induced hyponatremia, which occurs when serum sodium levels are less than 135 mmols per liter after endurance activities such as marathons or triathlons. This deficiency can be attributed to excess water intake and sodium loss from sweating and is a major concern because it can cause severe medical complications and even death.

What are the symptoms? Mild symptoms include weight gain, headache, vomiting, swollen hands and feet, fatigue, dizziness, and nausea but exercise-induced hyponatremia can actually be asymptomatic in mild cases).  Severe symptoms include altered mental status, confusion, seizures, coma, and mental changes called EAH encephalopathy.

An understanding of hydration has evolved over time. Previous thinking advised avoiding beverages while exercising, which reversed to drinking as much water as possible. Currently, the American College of Sports Medicine recommends preventing excessive dehydration without creating electrolyte deficiencies. The widely reported case of a 28 year old woman who died after the 2002 Boston Marathon, and others spurred many organizations like the American College of Sports Medicine to provide guidance on fluid status and replacement.

The prevalence of exercise-induced hyponatremia has been shown by research on endurance races. Almond et al recruited Boston Marathon participants in 2002 to estimate the prevalence and analyze the risk factors of hyponatremia. It was concluded that 13% of the runners experienced hyponatremia and 0.6% had critically low serum sodium levels of less than 120 mmol per liter. Weight gain after the race due to excessive fluid intakes was shown to be the strongest predictor of hyponatremia. Through these observations, it was projected that if all of the runners were surveyed, about 1,900 of the 15,000 race finishers would have had some degree of hyponatremia.

Hydration is critical for optimal performance, and it is important to find a balance in hydration to prevent dehydration and the consumption of excess fluids. In addition, it is critical for all endurance athletes to be aware of exercise-induced hyponatremia. Greater monitoring and regulation of fluid intakes needs to be provided for each athletic participant especially during ultra-endurance events.


Further readings:

  1. O’Connor RE. Exercise-Induced Hyponatremia: Causes, Risks, Prevention, and Management. Cleveland Clinic Journal of Medicine: 73 (3): 2006.
  2. Ackerman KE. Exercise-Associated Hyponatremia: A Sodium Paradox: 2009 <http://www.diabetes->
  3. Sawka MN, Burke LM, Eichner ER, Maughan RJ, Montain SJ, Stachenfeld NS. American College of Sports Medicine Position Stand: Exercise and Fluid Replacement. Medicine & Science in Sports & Exercise. 2007.
  4. Almon C, Skin AY, Fortescue EB, Mannix RC, Wypij D, Binstadt BA, Duncan CN, Olson DP, Salerno AE, Newburger JW, and Greenes DS. Hyponatremia Among Runners in the Boston Marathon. The New England Journal of Medicine: 352: 1550- 6, 2005.



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