Written by Shawn Radcliffe | Published on March 25, 2014
Medically Reviewed by George Krucik, MD, MBA on March 25, 2014

What Is Overhydration?

Nearly all the major systems of your body depend on water to work properly. Drinking plenty of water throughout the day aids in regulating body temperature, preventing constipation, flushing waste products out of the body, and many other important functions.

Most people, especially those who exercise in hot weather, are more concerned about not drinking enough water. However, overhydration—or drinking too much water—is also a potentially deadly condition, one that can throw off the balance between water and sodium in your blood.

Types of Overhydration

The amount of water in the body is carefully controlled by two processes: urine production in the kidneys, and the thirst response. This careful balance can be thrown off at either end, either because of disease or by a person consciously overriding his or her own thirst. When too much water collects in the body, it can lead to water intoxication or dangerously low levels of sodium in the blood (hyponatremia).

There are two types of overhydration: increased water intake and retaining water.

  • Increased water intake—or drinking more water than the kidneys can get rid of in the urine—can cause too much water to collect in the body.
  • When the body is unable to get rid of excess water, it is said to be retaining water. This happens with several medical conditions, for instance. It can be dangerous because it throws off the balance between water and sodium in the blood.

What Causes Overhydration?

Overhydration caused by drinking too much water can occur both consciously and unconsciously. For example, a person may drink too much water during exercise. Some medications can also cause dry mouth and cause an increase in thirst. Increased thirst can also be caused by uncontrolled diabetes. Psychiatric conditions such as schizophrenia (primary polydipsia or psychogenic polydipsia) can also cause compulsive water drinking.

Overhydration caused by water retention is often the result of medical conditions, such as:

  • liver disease (cirrhosis)
  • kidney problems
  • congestive heart failure
  • syndrome of inappropriate anti-diuretic hormone (SIADH)

What Are the Symptoms of Overhydration?

Symptoms of overhydration may not be recognized in the early stages but can include:

  • nausea and vomiting
  • headache
  • changes in mental state (confusion or disorientation)

If left untreated, overhydration can lead to dangerously low levels of sodium in the blood (hyponatremia). This can cause more-severe symptoms, such as:

  • muscle weakness, spasms or cramps
  • seizures
  • unconsciousness
  • coma

How Is Overhydration Diagnosed?

To determine whether symptoms are caused by overhydration or another condition, a doctor may conduct a medical history, a physical examination, and blood and urine tests.

How Is Overhydration Treated?

Treatment for overhydration depends upon the severity of the symptoms and the underlying reason. It may include:

  • cutting back on fluid and salt intake
  • diuretics to increase how much urine is produced
  • medications to reduce symptoms such as nausea, seizures, and headache
  • treatment of underlying medical conditions

How Can Overhydration Be Prevented?

Endurance athletes can reduce the risk of overhydration by weighing themselves before and after a race to determine how much water they have lost and need to replenish.

Individuals should avoid drinking more than one liter per hour of fluid. Drinking more fluids before and during a race or an intensive athletic exertion can also help you avoid the need to drink too much water afterwards. Sports beverages that contain the electrolytes sodium and potassium are also recommended, as both are lost in sweat.

If you have an underlying medical condition, such as diabetes, congestive heart failure, or kidney problems, talk to your doctor about the best treatments for those conditions. If you experience excessive thirst or an overly strong urge to drink water, contact your doctor before you develop symptoms—it could indicate a medical problem that requires treatment.

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