Sodium is an electrolyte that plays an essential role in regulating levels of water and other substances in the body. When sodium levels in the blood become too low, it leads to hyponatremia, causing symptoms that include lethargy, confusion, and fatigue.

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Hyponatremia is the most common electrolyte disorder — research suggests that approximately 1.7% of people in the United States have the condition. It is more prevalent among people with cancer.

It can result from underlying conditions, such as kidney failure, or other factors, including drinking too much water or taking certain medications.

As the condition worsens, individuals may experience symptoms, such as:

The definition of a low sodium level is below 135 milliequivalents per liter (meq/l). Severe hyponatremia occurs when levels drop below 125 meq/l. Health issues arising from extremely low sodium levels may be fatal.

Mild hyponatremia may not cause symptoms, but when they occur, they can include:

  • confusion
  • sluggishness
  • a headache
  • fatigue and low energy
  • nausea
  • restlessness
  • irritability

If hyponatremia symptoms worsen, it may cause significant illness, disability, or in extreme cases, death.

Acute hyponatremia may also lead to serious brain swelling that can cause permanent disability or death.

If the condition worsens, it can cause severe symptoms, particularly in older adults. Severe symptoms may include:

Doctors also associate mild chronic hyponatremia with the following complications:

Without adequate treatment, people with hyponatremia can develop:

  • rhabdomyolysis, where the skeletal muscle tissues die
  • altered mental status
  • seizures
  • a coma

Other medical conditions and factors that can cause sodium levels to fall include:

Taking the recreational drug ecstasy or MDMA also increases the risk of severe hyponatremia in some cases. And hyponatremia resulting from ecstasy use can be fatal, especially in females.

Hormone disorders are another known cause. These include Addison’s disease, which reduces the body’s production of the hormones cortisol and aldosterone. Additionally, hypothyroidism, which doctors characterize by low levels of thyroid hormone, is another potential cause of hyponatremia.

Learn more about how drinking too much water can lower sodium levels.

Certain factors increase the risk of developing hyponatremia, including:

  • older age
  • having specific conditions, such as SIADH or kidney, heart, or liver disease
  • taking certain diuretics, antidepressants, or pain medications
  • taking ecstasy
  • lifestyle factors, such as intense exercise, which may cause people to drink lots of water quickly

People at risk of hyponatremia or who develop symptoms should consult their doctor immediately, as they may need urgent medical treatment.

Individuals with symptoms, including vomiting, seizures, or loss of consciousness, require immediate attention. They should call an ambulance or go to the nearest emergency room.

To diagnose low sodium levels, a doctor will take a medical history, perform a physical examination, and order a blood test.

If the blood screening indicates low sodium levels, a healthcare professional will typically need to perform additional tests to determine the cause.

Treatment for hyponatremia involves restoring sodium levels and addressing what has caused them.

Restoring blood sodium levels

Those with mild-to-moderate hyponatremia due to lifestyle factors or medication could increase their sodium to usual levels by drinking less and adjusting or switching their medications.

Individuals with severe symptoms often require hospitalization and an intravenous sodium treatment to get their sodium levels back to usual. They may also require drugs to treat seizures or other hyponatremia symptoms.

Treating the underlying cause

Often, the cause of hyponatremia is an underlying condition, which will usually require specific treatment.

For example, if a person has liver disease, kidney disease, or heart disease, these can be potential causes of hyponatremia. These conditions may require treatment with medications or surgery.

People with a thyroid disorder can typically manage their symptoms and prevent hyponatremia and other complications with medications. They may also need to make certain lifestyle changes, such as avoiding smoking and reducing alcohol consumption.

SIADH usually requires ongoing treatment to prevent hyponatremia. Individuals with the condition may need to restrict their intake of fluids and take salt tablets and other medications.

To avoid low blood sodium levels, a person should:

  • avoid drinking excessive amounts of water
  • consume sports drinks during intense exercise
  • avoid taking ecstasy
  • seek treatment for medical conditions
  • discuss medications with a doctor
  • seek medical care if vomiting or diarrhea symptoms persist

The outlook for people with low sodium levels depends on the severity of the condition and the underlying cause.

Acute hyponatremia, which develops quickly, is more severe than chronic cases, which have a longer onset time. In severe cases, the condition can be fatal.

To improve their outlook, people should be aware of the symptoms of hyponatremia and seek prompt medical attention if they experience them. Those at risk of low sodium levels should be especially vigilant.