Extracellular fluid, blood volume, and nerve and muscle function.
Switzerland age 18–65: 2 g sodium/day; about 5 g table salt.
Mainly bread, cheese, processed meat, prepared foods, snacks and added salt.
Hyponatraemia is usually a water/regulation problem rather than simple dietary deficiency; symptoms range from nausea/headache to confusion and seizures.
Chronically high sodium intake raises blood pressure in many people and therefore cardiovascular risk.
Oedema is not a reliable salt or sodium-deficiency test and needs causal assessment.
For hyponatraemia: extreme fluid intake, endurance exercise, diuretics, heart/liver/kidney disease. For excess: high processed-food intake.
Always interpret serum sodium with fluid status, medicines and cause.
Salt tablets/electrolytes only situationally; reducing high intake is usually more relevant day to day.
Long-term excess promotes hypertension; sensitivity varies among people.