Symptoms, at-risk groups, and clinical context for sodium / electrolyte sodium deficiency. Sourced from NIH Office of Dietary Supplements and StatPearls.
Sodium deficiency from inadequate dietary intake is essentially unheard of in the modern world — most Americans consume ~3,400 mg/day, well above the 2,300 mg UL. Hyponatremia (serum <135 mmol/L) is the most common electrolyte disorder in clinical practice, but it's almost always caused by water excess, kidney issues, or medical conditions — not low salt intake. The framing here is imbalance, not deficiency.
Common symptoms
Headache, nausea, vomiting
Confusion, lethargy, or altered mental status
Muscle cramps or weakness
Restlessness or irritability
Loss of appetite
Severe acute hyponatremia: seizures, coma, brain swelling
Endurance athletes — exercise-associated hyponatremia from drinking too much plain water
At-risk groups
Endurance athletes who drink large volumes of plain water during long events (marathons, ultra-events)
People with SIADH (syndrome of inappropriate ADH secretion)
People with congestive heart failure, cirrhosis, or nephrotic syndrome
People taking thiazide diuretics, SSRIs, antipsychotics, or NSAIDs
Older adults (impaired water excretion, polypharmacy)
People with severe vomiting or diarrhea who replace fluids with plain water
People with adrenal insufficiency
People with primary polydipsia or extreme low-sodium diets combined with high water intake
When to see a doctorSudden confusion, severe headache, or seizures in someone who has been drinking large amounts of water — especially during endurance exercise — should be treated as a MEDICAL EMERGENCY. Note: most US adults should be focused on REDUCING sodium intake, not increasing it. The 2,300 mg/day limit is associated with reduced cardiovascular risk. Very low-sodium diets (<1,500 mg/day) without medical supervision can be problematic for some people.