Sodium
Primary extracellular electrolyte for fluid balance, blood pressure, and nerve conduction
Also known as
Definition
Sodium is the most abundant electrolyte in the extracellular fluid compartment and regulates osmotic pressure, fluid balance, blood pressure, and the excitability of nerves and muscles. The kidneys regulate sodium levels via the renin-angiotensin-aldosterone system (RAAS) and ADH. Disturbances (hyponatremia, hypernatremia) have far-reaching effects on the brain and cardiovascular system.
| Parameter | Value |
|---|---|
| Unit | mmol/l (mEq/l) |
| Reference Range | 135–145 mmol/l |
Agree on your personal target range with your doctor.
↓ What a low value means
Hyponatremia (< 135 mmol/l) arises from excessive water intake, SIADH (e.g., with pneumonia, CNS disease, medications such as SSRIs or thiazide diuretics), heart failure, liver cirrhosis, or kidney insufficiency. Symptoms: nausea, headache, confusion, seizures. Chronic hyponatremia increases the risk of falls and osteoporosis.
↑ What a high value means
Hypernatremia (> 145 mmol/l) develops from water loss (fever, diabetes insipidus, osmotic diuresis) or, rarely, excessive sodium intake. Symptoms: intense thirst, confusion, muscle weakness. Severe CNS damage possible above 155 mmol/l.
✓ What can influence this value
The sodium value in the blood is determined mainly by water balance and less by salt intake. It is influenced by fluid intake and fluid losses (fever, diarrhea), kidney, heart, and liver disease, hormones such as ADH and aldosterone, and medications such as thiazide diuretics or SSRIs. During long endurance efforts, a very high water intake can lower the value. The assessment is made by the treating doctor.
When to test
Sodium is part of many routine blood panels. Reasons for targeted testing include diuretic use, heart failure, liver disease, kidney insufficiency, altered consciousness, marathon or endurance sports, or suspected SIADH. With hyponatremia, osmolality and urine sodium help narrow down the cause.
Frequently asked questions
Can too little salt be harmful? +
Yes. Very low sodium intake can paradoxically increase cardiovascular risk by activating the RAAS and sympathetic nervous system, raising renin and aldosterone, and negatively affecting insulin resistance.
Why can sodium drop dangerously during intense endurance sports? +
Endurance athletes (> 4 hours of effort) can develop hyponatremia (exercise-associated hyponatremia, EAH) through excessive water intake without sodium replacement. This can be life-threatening.
What is the relationship between sodium and high blood pressure? +
High sodium intake raises blood pressure in 'salt-sensitive' individuals (~50% of hypertensives). Salt reduction lowers systolic blood pressure by ~3–5 mmHg. The response varies individually and depends on genetics (ACE polymorphism), kidney function, and potassium balance.
Sodium
Sources
Last updated: May 28, 2026
This information is for orientation only and does not replace medical advice. Reference ranges can vary by laboratory, method and country.