Understanding Nutrition and Health: What's the most common cause of hyponatremia?

October 8, 2025 •

5 min read

Affecting up to 30% of hospitalized patients, hyponatremia is the most common electrolyte disorder, but its causes are often misunderstood. Addressing the nutritional aspect, the answer to what's the most common cause of hyponatremia? is an imbalance of water relative to sodium, most frequently triggered by underlying medical conditions or specific dietary habits, not simply low salt intake.

Quick Summary

An excess of water relative to sodium is the most common cause of low blood sodium, or hyponatremia. This imbalance, which can be due to overhydration or fluid retention from underlying diseases like SIADH, dilutes the body's sodium levels, affecting critical bodily functions. Understanding the root cause is essential for effective treatment.

Key Points

Dilution is the Key Cause: The most common reason for hyponatremia is having too much fluid in the body relative to sodium, which creates a dilutional effect on the blood.
SIADH is a Frequent Culprit: Syndrome of Inappropriate Antidiuretic Hormone (SIADH), caused by excess ADH, is a leading cause of euvolemic hyponatremia, particularly among hospitalized patients.
Underlying Diseases Play a Major Role: Conditions such as heart failure, liver cirrhosis, and kidney disease are frequent causes by affecting fluid retention and balance.
Medications and Lifestyle Factors Can Induce It: Diuretics, antidepressants, certain recreational drugs, and over-consuming water during strenuous exercise (Exercise-Associated Hyponatremia) can all contribute.
Chronic Hyponatremia Increases Fall and Fracture Risk: Mild, chronic hyponatremia is associated with subtle neurological deficits like gait instability, leading to a higher risk of falls and fractures, particularly in older adults.
Dietary Habits Can Cause Imbalances: Specific nutritional deficiencies, such as a low-solute 'tea-and-toast' diet, can contribute to the development of hyponatremia.

What is Hyponatremia?

Hyponatremia is a condition where the sodium level in your blood is abnormally low, defined as a serum sodium concentration below 135 milliequivalents per liter (mEq/L). Sodium, a crucial electrolyte, helps regulate fluid balance both inside and outside your cells. When blood sodium levels drop, extra water enters the body's cells, causing them to swell. This can be particularly dangerous for brain cells, which have limited room to expand, leading to significant neurological symptoms in severe cases.

The Most Common Cause of Hyponatremia

While a variety of factors can contribute, the single most common cause of hyponatremia is an excess of total body water relative to total body sodium. This is a key nutritional and physiological point: the issue is often less about a lack of dietary sodium and more about a problem with fluid regulation that causes a 'dilution' effect in the blood. This can arise from several distinct mechanisms, which are often categorized by the body's fluid volume status: hypovolemic, euvolemic, and hypervolemic hyponatremia.

Hypovolemic Hyponatremia

In this state, both total body sodium and water decrease, but the loss of sodium is proportionally greater.

Gastrointestinal losses: Severe and prolonged vomiting or diarrhea can cause significant loss of sodium and fluids. Replacing these losses with only plain water further dilutes the remaining sodium.
Renal causes: The use of certain diuretics, especially thiazide diuretics, can increase the excretion of sodium in the urine.
Skin losses: Excessive sweating, particularly during prolonged endurance sports, can deplete sodium stores.

Euvolemic Hyponatremia

Here, total body water increases while total body sodium remains relatively normal. The most common driver of this state is the Syndrome of Inappropriate Antidiuretic Hormone (SIADH).

Syndrome of Inappropriate ADH (SIADH): This condition causes the body to produce too much antidiuretic hormone (ADH), also known as vasopressin. This hormone causes the kidneys to retain water, leading to a dilutional effect on sodium levels. SIADH can be triggered by a wide array of conditions, including certain cancers (especially small cell lung cancer), central nervous system disorders, pulmonary diseases, and numerous medications like SSRIs and pain relievers.
Excessive water intake (primary polydipsia): This is less common but can occur, often in individuals with psychiatric disorders, where a very high intake of plain water overwhelms the kidneys' ability to excrete free water.

Hypervolemic Hyponatremia

In this scenario, there is an increase in both total body sodium and water, but the increase in water is disproportionately larger. This leads to edema (swelling) and dilution of the blood sodium.

Congestive Heart Failure: The heart's inability to pump blood effectively leads to fluid buildup in the body, which dilutes sodium.
Cirrhosis: Advanced liver disease impairs the body's ability to regulate fluids, resulting in fluid accumulation in the body and diluted sodium levels.
Kidney Disease: Conditions like chronic renal failure impair the kidneys' ability to excrete excess fluid, causing fluid overload and dilution.

Nutritional Considerations in Managing Hyponatremia

Nutrition plays a complex and often crucial role in hyponatremia. In the context of underlying medical conditions, dietary adjustments are key, while in other cases, poor nutritional habits can be a direct cause.

The 'Tea-and-Toast' Syndrome: This term refers to hyponatremia seen in older adults with poor dietary intake. A diet consisting primarily of tea and toast is low in protein and sodium, reducing the body's overall solute load and limiting the kidneys' ability to excrete water.
Exercise-Associated Hyponatremia (EAH): Often seen in marathon runners and other endurance athletes, EAH is caused by drinking excessive amounts of plain water during a race, especially when coupled with significant sodium loss through sweat. It's a classic example of dilution from over-hydration. Consuming electrolyte-rich sports drinks can help mitigate this risk.
Low-Solute Diet: Conditions like 'beer potomania' result from consuming a large volume of low-solute fluid (e.g., beer) with minimal food intake, leading to water retention and hyponatremia.

Comparison of Acute vs. Chronic Hyponatremia


Feature	Acute Hyponatremia	Chronic Hyponatremia
Onset Time	Rapid (less than 48 hours)	Gradual (more than 48 hours)
Symptom Severity	Sudden and severe, often neurological	Milder, symptoms develop slowly, and the brain has time to adapt
Primary Danger	Rapid brain swelling (cerebral edema)	Risk of Osmotic Demyelination Syndrome (ODS) if corrected too quickly
Neurological Issues	Confusion, delirium, seizures, coma	Gait instability, attention deficits, memory impairment

Recognizing Symptoms and Seeking Care

Symptoms of hyponatremia can vary from mild to life-threatening, and may overlap with other conditions. Mild symptoms often include headache, fatigue, nausea, and muscle cramps. As the condition worsens, more severe symptoms like confusion, seizures, or coma can occur. Prompt medical evaluation is critical for proper diagnosis and treatment. In cases of severe, acute symptoms, it is considered a medical emergency requiring immediate treatment with careful intravenous fluid administration.

Dietary and Medical Management Strategies

Managing hyponatremia involves addressing the specific underlying cause. A healthcare provider will determine the fluid status and other factors to create a tailored treatment plan.

Fluid Restriction: For many cases involving excess body water (like SIADH or heart failure), restricting fluid intake is a primary strategy.
Addressing Underlying Conditions: Treating the root cause, such as kidney disease, liver failure, or a hormone imbalance, is paramount.
Medication Review: If medication is the cause, adjusting the dosage or switching to a different drug may be necessary.
Dietary Adjustments: For specific situations like exercise-associated hyponatremia or 'tea-and-toast' syndrome, a targeted dietary approach is needed. This might involve consuming electrolyte-rich drinks during endurance events or ensuring adequate protein and salt intake.
Hypertonic Saline: In severe, acute cases, administering a concentrated saline solution intravenously is necessary, but this requires close medical monitoring to avoid over-correction and complications like ODS.

Conclusion

While a simple lack of salt is rarely the singular issue, the most common cause of hyponatremia centers on a fluid imbalance. This dilution effect can be caused by excessive fluid intake, especially during intense exercise, but it is more frequently a consequence of underlying medical issues such as SIADH, heart failure, or kidney disease. Understanding the distinction between acute and chronic hyponatremia is also essential, as treatment strategies and the risks of correction differ significantly. Ultimately, proper diagnosis by a healthcare professional is the most critical step, and management often requires a combination of dietary adjustments, fluid restriction, and targeted treatment of the root cause. This complex interplay between hydration, nutrition, and systemic health underscores why hyponatremia demands careful medical supervision. Read more on nutrition and electrolytes for broader health insights.

Frequently Asked Questions

Yes, drinking excessive amounts of plain water, especially in a short period, can overwhelm the kidneys' capacity to excrete water. This dilutes the sodium in your blood, potentially causing hyponatremia, a condition also known as water intoxication.

SIADH stands for Syndrome of Inappropriate Antidiuretic Hormone. It is a condition where the body releases too much ADH, causing the kidneys to retain excessive water. This water retention dilutes the blood's sodium concentration, leading to euvolemic hyponatremia.

Heart and kidney diseases can impair the body's ability to excrete excess fluid effectively. In conditions like congestive heart failure or chronic renal failure, fluid builds up, causing a dilutional effect on blood sodium and resulting in hypervolemic hyponatremia.

Yes. Beyond simple sodium restriction, nutritional habits can contribute. The 'tea-and-toast' syndrome in older adults, where a low-solute diet restricts the kidneys' ability to excrete water, and 'beer potomania' from high-volume, low-solute fluid intake are specific dietary examples.

Symptoms can range from mild to severe. Common signs include nausea, vomiting, headache, fatigue, and muscle cramps. More severe cases can cause confusion, restlessness, seizures, or even coma.

Acute hyponatremia develops rapidly, typically in less than 48 hours, and poses a risk of brain swelling. Chronic hyponatremia develops more slowly, and while the brain has time to adapt, correcting it too quickly can be dangerous and lead to Osmotic Demyelination Syndrome.

Treatment varies depending on the cause and severity. It may involve fluid restriction, treating the underlying medical condition (e.g., heart or kidney disease), adjusting medications, or, in severe cases, administering intravenous fluids under careful medical supervision.

Yes, older adults are at a higher risk due to several factors, including age-related physiological changes, greater likelihood of chronic diseases, poor nutritional habits (like the 'tea-and-toast' diet), and more frequent use of medications that can affect sodium balance.