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The body of an average adult weighing 70 kg contains ~4200 mmol (~60 mmol/kg) of sodium. A total of 91% of the body sodium is in the extracellular fluid (ECF) and the remainder is the intracellular fluid (ICF).
Dietary sodium intake is 80 to 160 mmol/d. In individuals with a normal sodium balance, 95% of dietary sodium is filtered into the renal tubule, 4.5% with feces, and 0.5% through the skin. Less than 1% of sodium filtered into the renal tubule is excreted with urine, while the remaining sodium is reabsorbed.