High Sodium Symptoms: Causes, Signs & What to Do
High sodium almost always reflects dehydration rather than excess salt intake. This page covers the specific symptoms, likely causes, normal ranges, and when to act.
High serum sodium (hypernatremia) almost always reflects a water deficit rather than excess salt intake — the blood sodium concentration rises when the body loses more water than sodium. The brain is particularly sensitive to the resulting cellular shrinkage, and neurological symptoms dominate the clinical picture. See the Sodium biomarker overview for how it is measured alongside other electrolytes.
What High Sodium Means
Serum sodium concentration is tightly regulated by thirst, antidiuretic hormone (ADH), and the kidneys. When sodium rises above 145 mmol/L, it means water is disproportionately depleted relative to sodium. This draws water out of cells osmotically, causing them to shrink. In the brain, cellular shrinkage can cause mechanical traction on cerebral vessels and, in severe cases, intracranial hemorrhage.
Symptoms of High Sodium
- Intense thirst (the earliest and most consistent symptom)
- Dry mouth and mucous membranes
- Decreased urine output or very dark urine
- Fatigue and weakness
- Restlessness and irritability
- Confusion and disorientation (reflects brain cell shrinkage)
- Muscle twitching
Severe hypernatremia (above 155 mmol/L or rapid rise):
- Seizures
- Coma
- Intracranial hemorrhage from cerebral vein tearing during rapid brain shrinkage
What Causes High Sodium
- Inadequate water intake (most common in elderly, incapacitated patients, or infants)
- Excessive water loss without replacement — profuse sweating, prolonged diarrhea, high fever
- Diabetes insipidus (central or nephrogenic) — inability to concentrate urine leads to massive water loss
- Hyperosmolar hyperglycemic state (extreme hyperglycemia driving osmotic water loss)
- Hypertonic sodium infusions in hospital settings (iatrogenic)
- Primary adipsia (loss of thirst sensation from hypothalamic damage)
Normal Sodium Levels
| Measure | Reference Range | |---|---| | Sodium | 135-145 mmol/L | | Mild concern | 145-150 mmol/L | | Urgent threshold | Above 150 mmol/L warrants prompt evaluation | | Emergency threshold | Above 160 mmol/L |
When to See Your Care Team
Book a 1:1 consultation with a licensed care team lead if sodium is above 145 mmol/L on repeat testing, or if you have symptoms of confusion with a high reading. Sodium above 155 mmol/L is a medical emergency requiring hospital management. Rapid correction of hypernatremia is itself dangerous (cerebral edema) — correction must be gradual under clinical supervision.
Frequently Asked Questions
Does eating a high-salt diet cause high serum sodium?
Rarely. In healthy people with intact thirst and kidney function, excess dietary salt triggers thirst and increased ADH, which drives water retention and rapidly normalizes serum sodium. High serum sodium from dietary salt alone requires severely impaired water balance mechanisms.
What is diabetes insipidus?
Diabetes insipidus (DI) is a condition in which the body cannot concentrate urine — either because ADH is not produced (central DI from pituitary disease) or the kidneys do not respond to it (nephrogenic DI from medications like lithium, or hereditary). The result is massive water loss and hypernatremia if water intake cannot keep up.
How quickly should high sodium be corrected?
No faster than 10 to 12 mmol/L per day in most cases. Chronic hypernatremia that has developed over more than 48 hours requires even slower correction to prevent cerebral edema from too-rapid fluid shifts back into brain cells. This is a reason hospital management is essential.
Can high sodium affect the kidneys?
Yes. Prolonged hypernatremia impairs kidney concentrating ability and can cause acute kidney injury. The underlying cause of hypernatremia (dehydration, diabetes insipidus) is also often a direct renal stressor.
