Sodium.

Sodium is the major cation of extracellular fluid (ECF) and, because of its osmotic action, is involved in the regulation of ECF volume and blood pressure. The ingested sodium is almost completely absorbed by the intestine. Circulating sodium is filtered by the glomeruli and its renal tubular handling is responsible for the maintenance of sodium and water balance. Sodium deficiency is rare and occurs only in some medical conditions. High dietary sodium intake is associated with ECF volume expansion and is a leading risk factor for hypertension and cardiovascular diseases; it also adds to risk of gastric cancer, nephrolithiasis, reduced bone mineral density, and osteoporosis. Salt added while cooking and eating, the amount added during food transformation, and that occurring naturally in foods contribute to the dietary sodium intake. Additional small amounts of sodium may be occasionally acquired through oral or parenteral medications. The National Academy of Science, Engineering and Medicine set an adequate intake of 1.5 g and a chronic disease risk reduction intake of 2.3 g of sodium per day for the adult population. The European Food Safety Authority and the World Health Organization set a standard dietary target for sodium of 2 g/d (5 g of salt). Recent studies highlighted the relevance of salt intake reduction for all-cause mortality risk and, in particular, for stroke. Sodium also appears to affect the activity of the immune system by influencing the gut microbiota composition and the macrophage and lymphocyte differentiation.