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 |
| Optimal Range (lab2go) | 138–142 mmol/l (lab2go Optimum Zone; mid-range for optimal cellular hydration) |
↓ 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 fall risk 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.
✓ How to optimize this marker
Sodium intake: WHO recommends < 2000 mg/day (< 5 g salt). Western diets often contain 8–12 g salt/day. More important than reduction at normal values: adequate fluid intake (1.5–2.5 L/day) and balanced potassium intake (effectively lowers blood pressure in salt-sensitive individuals).
When to test
In every routine blood draw; mandatory with diuretic use, heart failure, liver disease, kidney insufficiency, altered consciousness, marathon/endurance sports, or suspected SIADH. With hyponatremia: measure osmolality and urine sodium to differentiate cause.
Frequently asked questions
Can too little salt be harmful? +
Yes. Very low sodium intake (< 1500 mg/day) can paradoxically increase cardiovascular risk by activating the RAAS and sympathetic nervous system, raising renin and aldosterone, and negatively affecting insulin resistance. The optimal sodium intake is 2–3 g sodium (5–7.5 g salt) per day.
Why is sodium dangerous 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. Recommendation: electrolyte drinks instead of plain water during long efforts; drink according to thirst.
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.
Sources
Last Reviewed: May 28, 2026 · sina
This information is for orientation only and does not replace medical advice. Reference ranges can vary by laboratory, method and country.