The Cooper Institute

Founded in 1970 by the "Father of Aerobics"
Kenneth H. Cooper MD, MPH


Can You Drink Too Much Water During Exercise?

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Today I Will TIW
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Thursday, Jun 20, 2013

One of the most common concerns during high summer temperatures is dehydration. But are you aware that over-hydration can be just as serious?

Dehydration is defined as excessive loss of body water. Over-hydration is more commonly referred to as hyponatremia and occurs when blood sodium levels drop below normal. The most common cause of hyponatremia is drinking too much plain water without adequate electrolytes, most importantly sodium. Sodium is an electrolyte which is necessary for transmitting nerve impulses and for proper muscle function. When sodium levels are outside the normal range, an electrolyte imbalance occurs. Plain water does not contain electrolytes; therefore, drinking a large amount can dilute sodium levels in the blood. There is a certain amount of sodium in your body and when you sweat, you not only lose water but sodium too. But if you only replace the lost water, the sodium concentration in the body will decrease. Now most individuals have enough sodium in their diet to account for the loss that occurs as a result of exercise but in extreme cases, especially when a large amount of plain water is consumed in a short period of time after a tremendous amount of sodium loss, hyponatremia can result. Symptoms of hyponatremia include confusion, fatigue, and muscle stiffness. There have even been reports of deaths. It is crucial to follow proper hydration guidelines when exercising for extended periods of time and in the heat. Someone about to participate in a bout of endurance exercise should follow proper hydration recommendations.  These guidelines can be found in a previous blog titled “Hydrating for Physical activity in the heat: don’t wait for a sprinkler to save you!”

Those most susceptible to hyponatremia are endurance athletes, or those working outdoors in the heat for extended amounts of time.  Some people also lose a little more sodium in sweat than others. If you find your clothes covered in salt after a workout, it may be a good idea to add a little salt to your meals before and after your time in the heat to replace the sodium losses.  However, you should consult your doctor before doing so if you have a history of high blood pressure. Not everyone is susceptible to hyponatremia. Elite marathoners typically do not suffer from hyponatremia because they finish quicker and don’t spend as much time at water stops. In addition, they drink sports drinks which contain adequate levels of sodium and other electrolytes.  It’s the slower runners that need to be careful. One study (Hew, 2005) found that women drank more water than men during the Houston marathon, therefore were more susceptible to hyponatremia!

Here is what American College of Sports Medicine (ACSM) recommends for sodium intake:

  • 47-118 mg/Cup before
  • 47-71 mg/Cup during
  • Add a little extra salt to meals after
Sports drinks are not the only sources of sodium. Many energy gels contain an adequate amount of sodium, however, many of their energy bar counterparts do not. Some energy gels have 200 mg of sodium per packet; while the same brand may have energy chewables with only 30 mg of sodium per packet. So be sure to read your labels and consume the right fluid replacement necessary to prevent dehydration and hyponatremia. Both are important to watch out for.

When running, I like to schedule stops every 1.5 miles for water and to consume an energy gel every 45 minutes. This equates to drinking 1 cup of water about every 13 minutes on average. Do you have specific techniques you use to remind yourself to stay hydrated? Have you ever suffered from hyponatremia? Share your personal experiences and tips for staying hydrated on Facebook.


American College of Sports Medicine; Sawka MN, et al. American College of Sports Medicine position stand. Exercise and fluid replacement. Med Sci Sports Exerc. 39:377-390, 2007.

Hew, T.D. Women hydrate more than men during a marathon race: hyponatremia in the Houston marathon: a report on 60 cases. Clin J Sport Med. 15(3) 148-153, 2005.

National institutes of health. (2013). Retrieved from