What Is Hyponatremia?

Hyponatremia is when the sodium level in your blood is too low. Sodium is an essential electrolyte that helps control blood pressure, maintain fluid balance, and regulate nerve and muscle function. Water enters the cells when your sodium levels are abnormally low, causing them to swell. Swelling can harm brain cells and cause symptoms such as headache, confusion, fatigue, nausea, irritability, and muscle weakness.

Hyponatremia is a common, usually temporary condition, affecting an estimated 5% of adults and 35% of hospitalized people. It can occur at any age but is most common in older adults. Certain medical conditions and lifestyle factors can cause hyponatremia, and a diagnosis is made through blood tests. Treatment for hyponatremia varies, depending on the cause and severity of the condition. 

Types

Understanding the type of hyponatremia you have is an important step in determining the underlying cause and appropriate treatment. Different types of hyponatremia are classified based on your fluid volume, meaning the amount and distribution of fluids in your body.

The main types of hyponatremia include:

• Hypovolemic hyponatremia: This occurs when there is a loss of water and an even greater loss of sodium in the body, leading to a decrease in blood volume. Conditions that result in fluid loss, such as kidney disease, diuretic medications, and excessive sweating from endurance sports can cause this type of hyponatremia.
• Euvolemic hyponatremia: This occurs when the amount of water in the body increases, but the sodium level remains the same. Conditions that affect the body’s ability to regulate water balance, such as Addison’s disease and hypothyroidism, and certain medications, such as opioids and barbituates, can cause this type of hyponatremia. 
• Hypervolemic hyponatremia: This occurs when there is an excess of water and sodium in the body, but the water increase is greater. This type of hyponatremia is often caused by conditions that cause fluid retention, such as heart disease or liver cirrhosis.
  

Hyponatremia can be acute or chronic, depending on how quickly symptoms develop.

• Acute hyponatremia: A rapid decrease in blood sodium level over a short period, typically within 48 hours. If your water intake exceeds your kidneys' ability to excrete electrolyte-free water, your body retains excess water. Symptoms develop quickly, and prompt medical attention is needed to avoid complications.
• Chronic hyponatremia: When your blood sodium level gradually decreases over a longer period (48 hours or more). Underlying conditions can cause chronic low blood sodium, and symptoms are usually milder but still require medical attention.

Hyponatremia Symptoms 

Symptoms of hyponatremia vary, depending on how low your blood sodium level is. Some people with mild hyponatremia may have no symptoms. The lower your blood sodium level, the more likely you are to experience symptoms.

Common symptoms of low sodium levels include:

• Headache 
• Fatigue or drowsiness 
• Nausea or vomiting 
• Confusion 
• Low blood pressure
• Loss of balance or dizziness 
• Muscle weakness
• Muscle cramps or twitching 
• Irritability
• Restlessness 
• Seizures
• Coma
  

Causes

Sodium is an essential electrolyte your body needs to function normally. The body can't make sodium, so you get it by eating foods that contain sodium. When you are vomiting or have diarrhea, a healthcare provider might tell you to drink an oral rehydration solution that contains sodium to ensure you stay hydrated and replenish the sodium your body loses when sick.

Hyponatremia occurs when your body has excess water relative to sodium in your blood. Certain health conditions, medications, and lifestyle factors can cause the sodium levels in your body to drop, leading to hyponatremia.

Common causes of low sodium include:

• Diarrhea
• Vomiting 
• Cirrhosis 
• Severe burns
• Hypothyroidism
• Pancreatitis 
• Brain disorders or injury 
• Syndrome of inappropriate antidiuretic hormone (SIADH), which is when the body makes too much antidiuretic hormone (ADH)
• Kidney diseases 
• Heart failure 
• Excessive sweating 
• Excessive thirst/too much water intake 
• Diuretic medications (water pills) 
• Pain medications 
• Antidepressant and antipsychotic drugs

Risk Factors 

Hyponatremia can affect anyone, but certain factors can increase your risk:

• Advanced age (older adults)
• Being female (assigned female at birth)
• Eating a low-sodium diet 
• Excessive water consumption 
• Extreme temperatures 
• Use of antidepressants, diuretics, or anti-inflammatory drugs 
• Low body weight 
• Exercising for four hours or longer (e.g., running a marathon) 
• Having kidney disease, heart failure, liver disease, or syndrome of inappropriate antidiuretic hormone (SIADH)

Diagnosis

Hyponatremia is diagnosed through a physical examination, medical history review, and laboratory tests. During the physical exam, a healthcare provider will ask about your symptoms. They will also review your medical history to determine if you have an underlying medical condition or take medications that can cause hyponatremia. 

Laboratory tests used to diagnose hyponatremia include:

• Blood test: Measures the amount of sodium in your blood. Hyponatremia is diagnosed if your levels are 135 milliequivalents per liter (mEq/L) or lower. Severe hyponatremia is diagnosed if blood sodium is 120 mEq/L or lower. 
• Urine test: Measures the sodium concentration in your urine and evaluates kidney function. 

Treatments for Hyponatremia  

Hyponatremia treatment focuses on slowly increasing the sodium level in the blood to relieve symptoms and prevent complications. Management of the underlying cause is also important when treating hyponatremia. 

Treatment varies depending on how low your blood sodium level is and may include the following:

• Fluid restriction: Mild hyponatremia is often treated by restricting fluid intake (less than 1 liter/day) to help restore sodium levels. If you take medication that causes hyponatremia, your dose may be lowered, or you may need to stop taking the medicine.
• Sodium replacement: Restoring sodium levels in the blood may be done through your diet (e.g., slowly increasing salt intake with food), or a sodium solution may be given intravenously (via IV) to increase sodium levels slowly. People with chronic hyponatremia may be prescribed salt tablets. 
• Diuretics: If the volume of water in your body is too high, you may be given diuretics to increase urine output and restore your electrolyte balance. 
• Vasopressin receptor antagonists: In cases where hyponatremia is caused by SIADH, medications that block the effects of vasopressin, a hormone that regulates fluid balance, may be prescribed. 

If hyponatremia is caused by an underlying medical condition such as heart failure or kidney disease, treatment and management of the condition are essential to correct sodium levels and prevent complications. 

Prevention

Strategies that may help prevent hyponatremia include:

• Avoid overhydration: Drinking excessive fluids, especially water, can dilute sodium in the blood. Drinking a healthy amount of fluid can help prevent hyponatremia.
• Manage associated conditions: Treating and managing associated conditions, such as kidney disease, can help you maintain a healthy blood sodium level. 
• Know the sodium content of foods and beverages: Consuming foods and beverages that are low in sodium can increase your risk of hyponatremia. Read labels and know the sodium content of your foods and beverages.
• Monitor medications: Certain medications, such as diuretics and antidepressants, can contribute to hyponatremia. Work with your healthcare provider to monitor your medications and adjust dosages if necessary.
• Monitor fluid intake during exercise: Athletes participating in endurance events like marathons may be at risk for hyponatremia due to excess fluid intake. If you participate in endurance exercises, monitor your fluid intake and talk to your healthcare provider about replacing water with sports beverages.
  

Complications 

If left untreated, hyponatremia can lead to complications. Potential complications depend on whether low blood sodium is acute (sudden onset) or chronic (gradual onset and/or recurrent episodes).

Acute hyponatremia is associated with an increased risk of serious complications and requires immediate medical attention. Complications of acute hyponatremia can include:

• Cerebral edema: Excess fluid accumulates in the brain, leading to swelling and increased pressure. This can cause headaches, confusion, seizures, coma, and brain injury. 
• Rhabdomyolysis: Rapid breakdown of muscles, releasing the muscle fiber contents into the bloodstream. This can overwhelm the kidneys and lead to kidney damage or failure. 
• Permanent brain damage: In severe cases, swelling in the brain can cause permanent damage to brain cells or death. 
  

Chronic hyponatremia is associated with an increased risk of complications when treated aggressively (e.g., sodium levels are restored too quickly rather than gradually). Complications of chronic hyponatremia can include:

• Osmotic demyelination syndrome: Occurs when blood sodium levels are corrected (treated) too quickly, which destroys the myelin sheath (the substance that surrounds nerve cells in the brain stem). Symptoms include slurred speech, weakness, trouble swallowing, and balance problems.
• Osteoporosis: Loss of bone mineral density and mass, causing bones to become weaker and increasing the risk of fracture. 
• Cerebral edema: Mild brain swelling over a long period can lead to attention deficits, unsteady gait (balance problems), behavior changes, and an increased risk of death. 

Living With Hyponatremia  

With the proper treatment, most people with hyponatremia recover fully. However, chronic hyponatremia may require ongoing management to prevent recurrent episodes and complications. If you have chronic hyponatremia, your healthcare provider may recommend lifestyle modifications to help maintain healthy sodium blood levels. This may include reducing your fluid intake, medication adjustments, and eating a balanced diet that is not low in sodium. Regular visits with your healthcare provider are important to monitor your sodium levels. 

In some cases, hyponatremia can cause changes in physical abilities or cognitive function, impacting your quality of life. Physical therapy or cognitive rehabilitation may help improve function and your overall well-being.