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Can Athletes Drink Too Much Water?

IMAGE It seems as if we could never drink enough water. After all, we're always being told to drink more.

That's not always the case for ultra-endurance athletes who spend long hours exercising. Sometimes, drinking too much water can actually be a problem. If they flood their bodies with excess water, they may fall victim to a potentially fatal condition called hyponatremia.

Causes of Hyponatremia

Hyponatremia is low sodium concentration in the body, specifically the extra-cellular fluid, which is the blood and the fluid around the body's cells.

Normal sodium levels run between 135-145 milliequivalents per liter (mEq/L). Hyponatremia is generally defined as a sodium level of 135 mEq/L or below.

When sodium concentration in the blood is critically low, symptoms like muscle weakness, disorientation, headache, fatigue, and nausea may occur. The most severe symptoms include seizures, respiratory arrest, coma, and death.

When Hyponatremia Is Likely

Hyponatremia is more likely to occur in the following situations:

  • Environments that are extremely hot
  • During long distance endurance events such as marathons, ultra-marathons and triathlons
  • During events that require high effort

Who Is Most at Risk for Hyponatremia?

Ultra-Endurance Athletes

Ultra-endurance athletes who enter such events as 100-mile races and Ironman competitions are most at risk. Hyponatremia can occur as early as 4 hours into an event, but it's more likely to happen after 6 to 10 hours of exercise.

Other Endurance Athletes

Non-elite marathon runners are also at risk. A study in the New England Journal of Medicine found that out of 488 runners who volunteered blood samples after completing the Boston Marathon, 13% had hyponatremia and 0.6% had critical hyponatremia. Risk factors for developing hyponatremia included: gaining substantial weight during the race, having a racing time greater than 4 hours, and having a low or high body mass.

How Can Endurance Athletes Prevent Hyponatremia?

Say Yes to SaltChoose Drinks WiselyWeigh In

Endurance athletes need to take preventive measures to head off hyponatremia. It's best to plan in advance how you will stay hydrated safely.

Ultra-endurance athletes may want to consider adding more salt to their diets so they begin events with a good supply of sodium. This is not necessary for most recreational athletes, since most diets typically contain enough sodium to make up for that lost when sweating.

All athletes should drink water before their events, but when you've been exercising for more than an hour, sports drinks or other fluids with sodium are better choices.

Experts disagree on how much fluid to drink during endurance events. One recommendation is to consume 5-10 ounces (150-300 milliliters) of fluid every 15-20 minutes. However other experts recommend that athletes avoid exceeding 13-26 ounces (400-800 millileters) per hour. As you gain experience, you will begin to know your own fluid needs and drink accordingly.

Athletes should weigh themselves before and after their long-distance events. In fact, some long-distance events may require that you do so. In most cases, dehydration is more likely to be a problem than hyponatremia. By weighing themselves, athletes will know if they're drinking too much or too little.

Checking body weight at the same time every day before and after an endurance event will help athletes gauge how much fluid they need to replace or if they've consumed too much fluid.


American College of Sports Medicine

American Running Association

Canadian Resources

Canadian Society of Exercise Physiology

Health Canada


Almond CSD, Shin AY, Fortescue EB, et al. Hyponatremia among runners in the Boston Marathon. N Engl J Med. 2005;352(15):1550-1556.

Cosca DD, Navazio F. Common problems in endurance athletes. Am Fam Physician. 2007;76(2):237-244.

Hyponatremia. EBSCO DynaMed Plus website. Available at: Updated January 20, 2016. Accessed October 10, 2017.

Hyponatremia. University of Connecticut website. Available at: Accessed October 10, 2017.

Seebohar B. Hyponatremia in endurance athletes. Team USA website. Available at: Accessed October 10, 2017.