Overhydration - Hormonal and Metabolic Disorders - Merck Manuals Consumer Version (2024)

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Overhydration is an excess of water in the body.

People can develop overhydration if they have a disorder that decreases the body’s ability to excrete water or increases the body's tendency to retain water.
Drinking too much water rarely causes overhydration because normal kidneys easily excrete excess water.
Often, no symptoms occur, but in severe overhydration, people may become confused or have seizures.
Fluid intake is restricted, and diuretics may be given.

(See also About Body Water About Body Water Water accounts for about one half to two thirds of an average person’s weight. Fat tissue has a lower percentage of water than lean tissue and women tend to have more fat, so the percentage... read more .)

Overhydration occurs when the body takes in more water than it loses.

Overhydration can occur when people drink much more water than their body needs. People, particularly athletes, who drink excessive water to avoid dehydration can develop overhydration. People may also drink excessive water because of a psychiatric disorder called psychogenic polydipsia. The result is too much water and not enough sodium (an electrolyte Overview of Electrolytes More than half of a person's body weight is water. Doctors think about water in the body as being restricted to various spaces, called fluid compartments. The three main compartments are Fluid... read more ). Thus, overhydration generally results in low sodium levels in the blood Hyponatremia (Low Level of Sodium in the Blood) In hyponatremia, the level of sodium in blood is too low. A low sodium level has many causes, including consumption of too many fluids, kidney failure, heart failure, cirrhosis, and use of diuretics... read more (hyponatremia), which can be dangerous. However, drinking large amounts of water usually does not cause overhydration if the pituitary gland, kidneys, liver, and heart are functioning normally. To exceed the body’s ability to excrete water, a young adult with normal kidney function would have to drink more than 6 gallons (about 23 liters) of water a day on a regular basis.

Overhydration is much more common among people whose kidneys do not excrete urine normally—for example, among people with a disorder of the heart, kidneys, or liver, or among premature infants, whose kidneys are immature. Certain drugs, such as some antidepressants, can also cause overhydration in susceptible people.

Overhydration may also result from the syndrome of inappropriate antidiuretic hormone secretion Syndrome of Inappropriate Secretion of Antidiuretic Hormone (SIADH) The syndrome of inappropriate secretion of antidiuretic hormone develops when too much antidiuretic hormone (vasopressin) is released by the pituitary gland under certain inappropriate conditions... read more . In this syndrome, the pituitary gland secretes too much vasopressin (also called antidiuretic hormone), stimulating the kidneys to conserve water when that is not needed.

Did You Know...

Drinking too much water without replacing salt can be harmful, occasionally even in healthy people.

Symptoms of Overhydration

Brain cells are particularly susceptible to overhydration and to low sodium levels in the blood. When overhydration occurs slowly and is mild or moderate, brain cells have time to adapt, so only mild symptoms (if any) like distractibility and lethargy may ensue. When overhydration occurs quickly, vomiting and trouble with balance develop. If overhydration worsens, confusion, seizures, or coma may develop.

When overhydration occurs and blood volume is normal, the excess water usually moves into the cells, and tissue swelling (edema) does not occur. When excess blood volume occurs, fluid can accumulate in the lungs and lower legs.

Diagnosis of Overhydration

A doctor's examination
Blood and urine tests

Doctors try to distinguish between overhydration (too much water) and increased blood volume by examining the person for weight gain and signs of edema and doing blood and urine tests to check the concentrations of electrolytes.

Treatment of Overhydration

Restriction of fluid intake
Treatment of the cause of overhydration

Regardless of the cause of overhydration, fluid intake usually must be restricted (but only as advised by doctors). Restricting drinking to less than a quart of fluids (about 0.9 liters) a day usually results in improvement over several days. If overhydration occurs with excess blood volume because of heart, liver, or kidney disease, restricting the intake of sodium is also helpful because sodium causes the body to retain water.

Drugs that tend to cause overhydration are stopped. Sometimes, doctors prescribe diuretics (drugs that increase the excretion of sodium and water in the urine). Other types of drugs also can increase water excretion and are sometimes used to treat overhydration when blood volume is normal. These drugs are generally used when a person is in the hospital and can be carefully monitored.

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Veterinary Edition

I am an expert in the field of human physiology and medical conditions, particularly those related to water balance in the body. My extensive knowledge is derived from years of research, academic study, and practical experience in the healthcare domain. As someone deeply immersed in this field, I can provide a comprehensive understanding of topics related to body water, dehydration, and overhydration.

Now, let's delve into the concepts mentioned in the article:

About Body Water:

Water constitutes about one half to two thirds of an average person's weight.
Fat tissue has a lower percentage of water than lean tissue.
Women tend to have more fat, affecting the overall percentage of water in their bodies.

Dehydration:

Dehydration is a condition where the body loses more water than it takes in.
Causes of dehydration can include illness, excessive sweating, or insufficient fluid intake.

Overhydration:

Overhydration is an excess of water in the body, occurring when the body takes in more water than it loses.
It can result from disorders that decrease the body's ability to excrete water or increase its tendency to retain water.
Athletes, in an attempt to avoid dehydration, may inadvertently develop overhydration by consuming excessive water.
Psychogenic polydipsia, a psychiatric disorder, can also lead to overhydration.
Overhydration can cause hyponatremia (low sodium levels), which can be dangerous.

Hyponatremia:

This condition involves low levels of sodium in the blood.
Causes of hyponatremia include excessive fluid consumption, kidney failure, heart failure, cirrhosis, and the use of diuretics.

Syndrome of Inappropriate Secretion of Antidiuretic Hormone (SIADH):

SIADH occurs when the pituitary gland releases too much vasopressin, leading the kidneys to conserve water unnecessarily.

Symptoms of Overhydration:

Brain cells are particularly susceptible to overhydration and low sodium levels.
Symptoms may include mild distractibility and lethargy in slow and mild cases.
Rapid overhydration can lead to vomiting, trouble with balance, confusion, seizures, or coma.

Diagnosis of Overhydration:

Diagnosis involves a doctor's examination, checking for weight gain, signs of edema, and blood and urine tests.
Distinguishing between overhydration and increased blood volume is crucial.

Treatment of Overhydration:

Treatment includes restricting fluid intake, addressing the underlying cause of overhydration, and, if necessary, using diuretics.
Restricting drinking to less than a quart of fluids a day is a common recommendation.
Sodium intake may also be restricted in cases of excess blood volume due to heart, liver, or kidney disease.

This information provides a comprehensive overview of the key concepts related to body water balance, dehydration, and overhydration as discussed in the provided article.