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Over-hydrating: The signs of hyponatremia and how to avoid it

When we begin exercising, one of the first things that come to mind is hydration. We bring our water bottles, stop at drinking fountains and know to continuously hydrate when exercising in the heat or when sweating to keep our body temperature low so we can perform at our best. We get so concerned about one issue that we completely forget about another one, over-hydration (hyponatremia). Over-hydration is very real and needs to be taken seriously. Due to the increased popularity with endurance athletic events hyponatremia is on the rise in the United States . Let’s start with the signs and symptoms of being over-hydrated.

Signs and Symptoms:

  • Nausea
  • Vomiting
  • Headache
  • Dizziness
  • Muscular twitching
  • Disorientation/Confusion
  • Incoordination
  • Fatigue
  • Loss of appetite
  • Muscle weakness
  • Physical exhaustion
  • Seizures
  • Tingling
  • Coma
  • Cardiac or Respiratory arrest


Scientifically speaking hyponatremia is a condition that occurs when the level of sodium in your blood is abnormally low. The most common cause for this is drinking too much water (the intake of water exceeds the capacity of the body to excrete water) during endurance sports. It is also caused by large sodium losses in sweat from those who are “salty sweaters.” Drinking large amounts of water or losing large amounts of sodium in sweat dilutes circulating plasma sodium concentration in the body causing the body’s water level to rise and swell. The swelling is what can cause a range of medical issues.

Who Is at Risk?

Endurance athletes need to be the most careful, especially those with less experience. The less experienced athletes with slower paces end up having longer race times. Longer race times mean more water consumption and sodium loss leading to an increased risk of developing hyponatremia.

How to Avoid Hyponatremia:

Understand that drinking water is very important, but there is a point where you are doing more harm than good. An easy test is to continue with your normal exercise routine and weigh yourself before and after activity.  If there is a weight gain you can conclude that you are consuming more water than necessary and potentially putting yourself at risk.  In fact, of the runners tested at the Boston Marathon in 2002 who developed hyponatremia, 73% had gained weight.   If you begin to feel some of the signs and symptoms of hyponatremia, try and urinate to bring your water level back to normal.  At that point an electrolyte heavy sport drink won’t help, because the amount of sodium in sports drinks is relatively low compared to the volume of fluid so this will be counterintuitive.  

Simply knowing the signs and symptoms and the associated risks of hyponatremia is the first step towards safe marathon running.    

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