An Overview of Hyponatremia (Low Sodium)

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Hyponatremia is when the concentration of sodium in your blood is lower than what is needed for your body to function normally. Low sodium levels can affect blood pressure, muscle contractions, and the delivery of nerve signals.

Mild cases may not cause notable symptoms, but severely low levels of sodium can cause serious and even life-threatening symptoms. This is because your body will become overwhelmed with fluid, causing cells to swell and organs to malfunction.

One or more factors can cause hyponatremia, including medications and medical conditions that disrupt the balance of water and sodium in the body. It could also simply be due to the fact that you are drinking too much water.

This article takes a closer look at the various symptoms and causes of hyponatremia. It also explains how the condition is diagnosed and treated.

Spilt over salt shaker on table
Jose Luis Agudo / Eye Em / Getty Images 

Symptoms of Low Sodium Levels

While people with mild hyponatremia often have no symptoms, the likelihood of them occurring increases the more that sodium levels drop.

Common signs and symptoms of low sodium include:

  • Headaches
  • Fatigue or low energy
  • Drowsiness
  • Irritability or restlessness
  • Dizziness or loss of balance
  • Loss of appetite
  • Nausea or vomiting
  • Reduced urine output
  • Profuse or sudden sweating
  • Muscle cramps or spasms
  • Muscle weakness
  • Trouble concentrating
  • Mental confusion
  • Changes in personality
  • Seizures
  • Loss of consciousness

Complications of Low Sodium Levels

The complications of hyponatremia vary somewhat depending on whether it is acute (occurring suddenly and severely, usually as a result of a serious medical event) or chronic (meaning persistent or recurrent, usually as a result of a long-standing medical condition).

With acute hyponatremia, the rapid decline in blood sodium can lead to serious and sometimes irreversible health complications. Due to the rapid increase of fluids in the brain and other organs, a person with acute hyponatremia may experience:

  • Cerebral edema: This is the swelling of the brain due to overload of build, a condition that can lead to coma, ongoing seizures, and permanent brain injury.
  • Rhabdomyolysis: This is the rapid breakdown of muscles. This overloads the body with substances that can damage the kidneys and lead to acute kidney failure and permanent kidney damage.
  • Cardiopulmonary arrest: This is when the heart and lungs suddenly stop working, leading to death. This is directly associated with cerebral edema and the effect it has on the parts of the brain that regulate these functions.

Chronic hyponatremia tends to be less severe but is insidious because it can silently damage organs over time even at milder levels. Complications include:

  • Osteoporosis: This is when the loss of bone minerals causes bones to become brittle and break. The loss of sodium directly triggers declines in calcium levels which bones need to stay strong.
  • Cerebral edema: Even mild brain swelling can have adverse effects over time, leading to an unsteady gait, attention deficit, changes in behavior, and an increased risk of death.

Even with the normalization of sodium levels, the damage caused by chronic hyponatremia may not be reversible.

What Causes Hyponatremia?

Sodium is an essential mineral that your body cannot make. The only way to get it is through the foods you eat. If you do not get enough or lose more than you take in, hyponatremia can occur.

It is uncommon to have low sodium levels in the United States. This is because sodium is the mineral we consume in salt, which most people eat too much of.

Hyponatremia may also be caused by lifestyle factors or medical conditions that affect the balance of water and/or sodium in the body.

Lifestyle Factors

Dietary and lifestyle issues rarely affect sodium levels. Even so, the rapid loss of fluid and/or the excessive intake of fluid can cause sodium concentrations to plummet.

Excessive sweating can cause the rapid loss of sodium. Sweat and other body fluids are high in sodium. If you are unable to properly replenish sodium supplies after heavy sweating, sodium levels can drop precipitously.

If you drink excessive amounts of water after sweating without replacing electrolytes (essential minerals like sodium, calcium, and potassium), sodium levels can drop even further. This is because you are diluting the amount of sodium per volume of water in the body.

It is also possible to get hyponatremia through extreme sodium-free diets. Drinking too much water (overhydration) further increases the risk.

Medical Causes

There are medical conditions that can cause hyponatremia. Some develop slowly over time with symptoms developing gradually. Others develop rapidly with symptoms developing abruptly.

Medical causes of hyponatremia include:

  • Adrenal insufficiency: The adrenal glands produce a hormone called aldosterone which balances sodium and potassium levels in the body. Adrenal insufficiency, also known as Addison's disease, disrupts this balance.
  • Cerebral salt wasting syndrome (CSWS): This rare condition in which a brain injury alters the function of the kidneys, causing them to clear excessive amounts of sodium from the body.
  • Cirrhosis: This is the scarring of the liver, the condition of which can cause fluid retention. The level of retention increases in tandem with the severity of the liver damage.
  • Congestive heart failure: This is the inability of the heart to efficiently pump blood through the body, causing fluid build-up and the onset of hyponatremia.
  • Diarrhea: Severe diarrhea can lead to a condition called hypovolemia in which the extreme loss of fluid can cause hyponatremia.
  • Diuretics: Also known as "water pills," these drugs treat high blood pressure by increasing the passing of urine. This can deplete excess amounts of sodium from the body.
  • Ecstasy: This is a recreational amphetamine drug that has been linked to severe and sometimes fatal cases of hyponatremia.
  • Syndrome of inappropriate anti-diuretic hormone (SIADH): This is an uncommon disorder that causes the overproduction of anti-diuretic hormone (ADH), causing your body to retain water instead of excreting it in urine.


Hyponatremia is diagnosed with a physical exam, lab tests, and a review of your medical history. Central to the diagnosis is a blood test that measures the concentration of sodium in your blood.

The levels are measured in milliequivalents per liter (mEq/L) and classified as follow:

  • Normal: 135 to 145 mEq/L
  • Hyponatremia: Under 135 mEq/L
  • Severe hyponatremia: Under 120 mEq/L

The physical exam and medical history provide clues as to the underlying cause. Tests will check for abnormalities in your blood pressure, urine volume, and urine concentration. Other blood tests may look for abnormalities in your adrenal hormone levels or liver function.

Your healthcare provider will also check for neurological (nervous system-related) problems such as a loss of alertness, concentration, or orientation.

Hyponatremia Treatment

The treatment of hyponatremia can be simple at times and challenging at others. The treatment is often based on the slow and careful replacement of sodium in the body, as well as the management of the underlying cause of hyponatremia.

Dietary Intake

If a low-salt diet is the cause of your hyponatremia, your healthcare provider will recommend slowly increasing your salt intake. The recommended sodium intake is around one teaspoon of salt per day for adults and 1/2 teaspoon of salt per day for children.

Keep in mind that the salt in processed foods, bread, pasta, sauces, and even desserts counts toward the daily recommended intake.

You will also be advised to drink enough water—around 12 cups per day for females and 16 cups per day for males—but not to overhydrate.

Intravenous Sodium Replacement

If you have severe hyponatremia, you may need sodium to be replaced with intravenous (IV) fluids. This is when fluids containing water, sodium, and other key electrolytes are delivered gradually by "drips" into a vein using a needle.

The medical team will restore the sodium level over the course of several hours or days, depending on the severity of your condition.

Risks of IV Sodium Replacement

The intravenous replacement of sodium needs to be done gradually. If delivered too quickly, sodium can damage the protective coating around nerves cells in the brain, referred to as osmotic demyelination. This can lead to long-lasting and even permanent brain injury.


There are few medications that are consistently effective in treating hyponatremia.

Drugs called vasopressin receptor antagonists are sometimes used in people who have fluid retention and avoided in those with low fluid volumes. These drugs work best in people with congestive heart failure, cirrhosis, and SIADH.

Declomycin (demeclocycline) is an antibiotic sometimes used to treat SIADH. The results can vary, with some people experiencing an overcorrection of sodium levels. The drug can also cause kidney problems and photosensitivity (sensitivity to the sun) in some.


Hyponatremia is abnormally low levels of sodium in the blood. It can be diagnosed with a blood test.

A person with hyponatremia will have no symptoms if sodium levels are mildly decreased. When sodium levels drop significantly, hyponatremia can cause headache, fatigue, nausea, vomiting, muscle cramps, and difficulty concentrating. Severe cases can lead to seizures, coma, kidney failure, and death.

Hyponatremia can have several causes, including severe diarrhea, no-salt diets, overhydration, use of diuretics, congestive heart failure, certain hormonal problems, and cirrhosis.

The treatment may involve increased salt intake for mild cases and intravenous sodium replacement for severe ones.

Frequently Asked Questions

  • Can low sodium cause a stroke?

    Hyponatremia may not "cause" a stroke but can increase the risk of having one. It is also associated with worse outcomes if a stroke does occur. Some studies report that one in three people with stroke has hyponatremia.

  • Do sodium levels affect vision?

    Neither low sodium (hyponatremia) nor high sodium (hypernatremia) has any known effect on vision. There have been cases where hypernatremia in newborns has caused severe damage to the retina, but this is extremely rare.

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Additional Reading

By Peter Pressman, MD
Peter Pressman, MD, is a board-certified neurologist developing new ways to diagnose and care for people with neurocognitive disorders.