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The Dangers of Hyponatremia: Better Dehydrated Than Overhydrated During Exercise

Sep 21, 2015

An updated position statement on the dangers of hyponatremia (also known as water intoxication) was just released (1). It once again highlights how drinking too much water or any fluids during physical activity in the hopes of preventing dehydration can be potentially fatal.

The problem is that an excessive intake of fluids dilutes the sodium levels in the blood (natrium is the chemical symbol for sodium, which is found in table salt and other types of “salts”), and severely low sodium levels can lead to brain swelling, seizures, coma, and death. Other, less severe, symptoms of hyponatremia include nausea and vomiting, headache, confusion, loss of energy and fatigue, restlessness and irritability, and muscle weakness, spasms or cramps.


Hyponatremia has become a problem in recent years following the push to stay hydrated during all exercise, but until recently has primarily been associated with marathon races and other prolonged endurance events, especially among slow participants. Their main problem is that they don’t sweat that much, but they drink at every opportunity, often to excess over many hours due to fear of getting dehydrated. More recently, though it has been reported as being a problem among other types of athletic events, including half-marathons, sprint triathlons, long hikes, yoga classes, and team sport practices and games, particularly football played at all levels of competition.

Drinking sports drinks or other fluids with electrolytes in them can help a little bit, but hyponatremia appears to be more related to the total fluid intake—any type of fluids—and not whether or not the drinks contain some sodium in them (2). Sports drinks containing added sodium are still more dilute than plasma, and drinking any fluids in excess during exercise can lower blood sodium levels.

That said, exercise-associated hyponatremia is almost completely preventable, but it takes knowledge and a better understanding of hydration during physical activity. The key is simply for sporting participants to drink when they feel thirsty — not before and not after they feel like they are no longer thirsty. It really isn’t necessary to stay ahead of your thirst. The small impact that a slight bit of dehydration is going to have on your performance is nothing compared to the medical emergency created by drinking too much. This new report concludes that listening to your “innate thirst mechanism” provides a safe and reliable guide to hydration (1).

Using thirst as your guide should not increase your risk for cramping either since dehydration may only contribute minimally to this issue. Cramps may be more associated with neuromuscular fatigue than dehydration/electrolyte losses, and mild dehydration is not associated with increased cramping (3). Even participants who exercised and sweated in the heat until they had become severely dehydrated were no more prone to muscle cramps than they had been at the start (4).

Surprisingly, becoming dehydrated during exercise will not necessarily increase the risk of developing a heat-related illness like heat stroke either. A body mass loss of up to 3% (mostly fluid losses through sweating) was found to be tolerated by well-trained triathletes during an Ironman competition in warm conditions without any evidence of heat illnesses (5). In fact, athletes who collapse from heat illness often are quite well-hydrated, and it’s more likely that cramping and heat illnesses come from exercising too intensely. Muscles are more prone to spasms when fatigued, and heat illnesses generally occur in individuals unaccustomed to exercising in the heat and who continue to exercise even as they start to feel unwell.

A related issue addressed in a new study is that people with diabetes are more likely to have electrolyte imbalances (e.g., sodium and potassium) to start with, including hyponatremia associated with extended hyperglycemia (6). As discussed in a recent article about this research in Diabetes In Control (http://www.diabetesincontrol.com/articles/53-diabetes-news/18464-beware-diabetes-results-in-significant-electrolyte-disturbances#unused), the increased risk of electrolyte disturbances can result from poorer blood glucose management, the drugs used to treat diabetes (some which alter electrolyte balance), and the organ damage associated with diabetes (such as nephropathy).

In summary, preventing overhydration during exercise is likely more important that worrying about the effects of dehydration. Use thirst as your guide when you exercise, and avoid consuming excess fluids, especially during prolonged workouts or sporting events. Also, keep your blood glucose levels in better control overall prior to engaging in any activities to ensure that hyponatremia is not an issue.


  1. Hew-Butler T, Rosner MH, Fowkes-Godek S, et al. Statement of the 3rd International Exercise-Associated Hyponatremia Consensus Development Conference, Carlsbad, California, 2015. Br J Sports Med. 2015 Jul 30. pii: bjsports-2015-095004. doi: 10.1136/bjsports-2015-095004. [Epub ahead of print] (http://www.ncbi.nlm.nih.gov/pubmed/26227507)
  2. Dugas J. Sodium ingestion and hyponatraemia: sports drinks do not prevent a fall in serum sodium concentration during exercise. Br J Sports Med. 2006 Apr; 40(4): 372. doi: 10.1136/bjsm.2005.022400 PMCID: PMC2577547 (http://www.ncbi.nlm.nih.gov/pubmed/16556798)
  3. Miller KC, Mack GW, Knight KL, et al. Three percent hypohydration does not affect threshold frequency of electrically induced cramps. Med Sci Sports Exerc. 2010 Nov;42(11):2056-63. doi: 10.1249/MSS.0b013e3181dd5e3a. (http://www.ncbi.nlm.nih.gov/pubmed/20351595)
  4. Braulick KW, Miller KC, Albrecht JM, Tucker JM, Deal JE. Significant and serious dehydration does not affect skeletal muscle cramp threshold frequency. Br J Sports Med. 2013 Jul;47(11):710-4. doi: 10.1136/bjsports-2012-091501. (http://www.ncbi.nlm.nih.gov/pubmed/23222192)
  5. Laursen PB, Suriano R, Quod MJ, et al. Core temperature and hydration status during an Ironman triathlon. Br J Sports Med. 2006 Apr;40(4):320-5; discussion 325. (http://www.ncbi.nlm.nih.gov/pubmed/16556786)
  6. Palmer BF, Clegg DJ. “Electrolyte and Acid-Base Disturbances in Patients with Diabetes Mellitus.” N Engl J Med. 2015;373(6):548-59. (http://www.ncbi.nlm.nih.gov/pubmed/26244308)

As a leading expert on diabetes and exercise, I recently put my extensive knowledge to use in founding a new information web site called Diabetes Motion (www.diabetesmotion.com), the mission of which is to provide practical guidance about blood glucose management to anyone who wants or needs to be active with diabetes as an added variable. Please visit that site and my own (www.shericolberg.com) for more useful information about being active with diabetes.


About Dr. Sheri Colberg, Ph.D., FACSM

(Advisory Board Member) Sheri Colberg, PhD, also known as Sheri Colberg-Ochs, is an author, exercise physiologist, and professor emerita of exercise science at Old Dominion University and a former adjunct professor of internal medicine at Eastern Virginia Medical School, both in Norfolk, Virginia. Having earned her undergraduate degree from Stanford University and a Ph.D. from the University of California, Berkeley, she has specialized in research on diabetes and exercise and healthy lifestyles and shaped physical activity recommendations for professional organizations, including the American College of Sports Medicine, American Diabetes Association, and American Association of Diabetes Educators. She has authored 11 books, along with 24 book chapters and more than 300 articles on physical activity, diabetes, healthy lifestyles, and aging. In addition to her educational website, Diabetes Motion (www.diabetesmotion.com), she is also the founder of an academy for fitness and other professionals seeking continuing education enabling them to effectively work with people with diabetes and exercise: Diabetes Motion Academy (www.dmacademy.com). These and her own website (www.shericolberg.com) offer additional information about being active with diabetes. She is the 2016 recipient of the American Diabetes Association’s Outstanding Educator in Diabetes Award.