Hyponatremia is an electrolyte imbalance in which the sodium level in the body is abnormally low. Because sodium helps to regulate the way the body retains fluid, too little sodium results in the accumulation of too much water in the cells. Cellular swelling can cause many medical problems, ranging from mild to potentially fatal. Hyponatremia is most frequently the result of drinking too much water, and is a common medical problem for marathon and triathlon athletes.

Types of Hyponatremia

There are three types of hyponatremia:

  • Euvolemic hyponatremia (water increases, but sodium remains constant)
  • Hypervolemic hyponatremia (sodium and water increase, but water gain is greater)
  • Hypovolemic hyponatremia (water and sodium decrease, but sodium loss is greater)

All three types result in an imbalance in the body's ratio of salt to water.

Causes of Hyponatremia

There are a number of causes of hyponatremia; they include the following:

  • Diuretics, and certain antidepressant and pain medications
  • Heart failure
  • Liver or kidney problems
  • Syndrome of inappropriate antidiuretic hormone (SIADH)
  • Severe vomiting, diarrhea or sweating
  • Over-consumption of water
  • Dehydration
  • Severe burns over a large area
  • Ecstasy (an illegal drug)

Each of the causes listed interferes with the balance of fluids in the body and, therefore, affects the level of sodium in the blood.

Symptoms of Hyponatremia

Symptoms of hyponatremia are varied because an electrolyte imbalance affects many of the body's systems. Symptoms may include the following:

  • Confusion
  • Nausea and vomiting
  • Headache
  • Fatigue and loss of energy
  • Restlessness and irritability
  • Muscle weakness, cramps or spasms
  • Seizures
  • Coma

Certain people are at greater risk for hyponatremia. They include older adults; those with diseases or on medications that may precipitate an electrolyte imbalance; athletes who engage in intensive exercise; and suspected drug-abusers. For those who fall into one of these categories, hyponatremia should be suspected if one or more of the above symptoms is present.

Diagnosis of Hyponatremia

In addition to a physical examination, hyponatremia is diagnosed through blood and urine tests. These tests are essential because the symptoms of hyponatremia are common to a variety of other ailments.

Treatment of Hyponatremia

In mild cases of hyponatremia, reducing fluid intake may be all that is necessary to bring sodium levels back to normal. More severe cases can require further medication, administration of intravenous saline, or hormone therapy.

Additional Resources