Hyponatremia occurs when the sodium level in your blood becomes abnormally low. Sodium is essential for keeping your body’s fluids in balance, allowing nerves to function properly, and enabling muscles—including the heart—to contract normally. When sodium levels drop, water moves into your cells and causes them to swell. This swelling affects the brain the most, leading to symptoms that range from mild confusion to seizures and coma. Hyponatremia can develop slowly over days or rapidly within hours, and the speed of onset determines how dangerous it becomes. Although common in hospitalized patients and people with certain medical conditions, early recognition and prompt treatment can prevent serious complications.
Overview
Hyponatremia is defined as a blood sodium level below 135 mEq/L. Sodium plays a crucial role in maintaining the balance of water inside and outside cells. When sodium levels fall, excess water enters cells and makes them swell. In the brain, where there is limited room for expansion, this swelling can be life-threatening.
There are two major patterns of hyponatremia: acute, which develops within 48 hours and can cause sudden severe neurological symptoms; and chronic, which develops slowly and allows the brain to adapt but still carries risks if sodium becomes too low.
Hyponatremia is common in hospitalized patients, older adults, endurance athletes, and people taking certain medications. It can result from drinking too much water, losing too much sodium, or from medical conditions that cause the body to retain excessive water.
Causes
Hyponatremia develops when the balance between water and sodium is disrupted—either from too much water, too little sodium, or both.
- One of the most common causes is excess water retention, often due to conditions like heart failure, liver cirrhosis, or kidney disease. In these conditions, the body holds onto water even when it shouldn’t.
- Syndrome of inappropriate antidiuretic hormone secretion (SIADH) is another major cause. In SIADH, the body releases too much antidiuretic hormone (ADH), causing water retention and dilution of sodium.
- Medications such as diuretics, antidepressants (SSRIs), antipsychotics, carbamazepine, and some pain medications can trigger hyponatremia.
- Severe vomiting or diarrhea, especially if prolonged, can lead to sodium loss.
- Thiazide diuretics, used to treat high blood pressure, are well known for causing hyponatremia, especially in older adults.
- Excessive water intake, such as in endurance athletes or psychiatric water-drinking behaviors, dilutes sodium levels.
- Adrenal insufficiency, including Addison’s disease, reduces aldosterone levels and leads to sodium loss.
- Hypothyroidism can also contribute to low sodium.
- In some cases, a combination of factors—such as poor intake, medications, and illness—can work together to cause sodium deficiency.
Symptoms
Symptoms depend on how quickly sodium levels fall and how low they become.
Mild hyponatremia may cause:
- Headache
- Nausea
- Fatigue or low energy
- Difficulty concentrating
- Irritability
Moderate hyponatremia often leads to:
- Confusion
- Vomiting
- Unsteadiness or falls
- Muscle cramps or spasms
Severe or rapidly developing hyponatremia can cause:
- Seizures
- Loss of consciousness
- Severe confusion or agitation
- Coma
- Respiratory arrest
Because the symptoms overlap with many other conditions, measuring blood sodium is critical to making the diagnosis.
Diagnosis
Diagnosis begins with a blood test showing sodium below 135 mEq/L. From there, determining the cause requires additional evaluation.
Doctors assess your fluid status—whether you appear dehydrated, normal, or overloaded with fluid.
Further tests often include:
- Serum osmolality
- Urine sodium
- Urine osmolality
- Kidney, thyroid, and adrenal function tests
- Medication review
The combination of these results helps determine whether the hyponatremia is due to water excess, sodium loss, or hormonal imbalance.
Identifying the underlying cause is essential for choosing the right treatment.
Treatment
Treatment depends on the severity of symptoms, how quickly sodium levels dropped, and the underlying cause.
For mild cases, treatment may involve:
- Limiting fluid intake (fluid restriction)
- Adjusting medications causing water retention
- Treating underlying problems such as hypothyroidism or adrenal insufficiency
For moderate to severe cases, treatment may include:
- Intravenous saline solutions, such as isotonic or hypertonic (3%) saline, to raise sodium levels
- Medications that block ADH (called vaptans) in certain cases
- Stopping contributing medications, such as thiazide diuretics
In emergency situations with seizures or severe confusion, hypertonic saline is given carefully to prevent brain swelling.
A crucial point in treatment is not correcting sodium too quickly. Rapid correction can cause a serious neurological condition called osmotic demyelination syndrome, which can lead to permanent brain damage. Because of this risk, sodium correction rates are monitored closely in the hospital.
What Happens If Left Untreated
Untreated hyponatremia can lead to worsening brain swelling, increasing the risk of:
- Severe confusion
- Seizures
- Permanent neurological injury
- Coma
- Death
Even chronic mild hyponatremia increases the risk of falls, fractures, attention problems, and reduced quality of life—especially in older adults.
Severe hyponatremia is a medical emergency and requires immediate treatment to prevent life-threatening complications.
What to Watch For
If you are at risk for hyponatremia or have had it before, pay attention to:
- New or worsening confusion
- Severe headaches
- Nausea or vomiting
- Difficulty walking or frequent falls
- Muscle weakness or cramping
- Unusual fatigue
- Seizure-like activity
Notify your healthcare provider if these symptoms occur, especially if you recently started a new medication or changed your fluid intake.
Those with chronic medical conditions (heart failure, liver disease, kidney problems) should monitor fluid intake and follow medical recommendations closely.
Living with Hyponatremia
Living with or being prone to hyponatremia requires understanding and managing the factors that contribute to low sodium.
Important steps include:
- Following fluid-restriction guidelines when advised
- Taking medications exactly as prescribed and reporting side effects
- Avoiding excessive water intake, especially during exercise
- Monitoring weight changes or swelling in people with heart failure
- Ensuring good nutrition and electrolyte balance
- Getting regular blood tests if you are on diuretics or antidepressants
People with chronic SIADH may need long-term treatment strategies, including moderation of fluid intake or specific medications.
Education is key—knowing early symptoms helps prevent severe episodes.
Key Points
- Hyponatremia occurs when sodium levels in the blood become too low, causing water to move into cells and leading to swelling—especially in the brain.
- Symptoms range from mild confusion to seizures and coma. The speed of onset determines how dangerous the condition becomes.
- Common causes include water retention, medications, hormonal disorders, excessive water intake, and sodium loss from vomiting or diarrhea.
- Diagnosis requires blood sodium testing plus urine and hormone evaluations to identify the underlying cause.
- Treatment involves fluid restriction, medication adjustments, or saline infusions, depending on severity. Sodium must be corrected slowly to avoid neurological complications.
- Without treatment, hyponatremia can be life-threatening due to brain swelling.
- With proper monitoring, medication management, and awareness of symptoms, most people can safely manage or prevent hyponatremia.
