Sodium is an essential electrolyte required for fluid balance, nerve conduction, and muscle function; no formal citation is needed for this basic physiological fact.
The claim that a minimum daily sodium intake is physiologically required for normal bodily function is a fundamental, well-established biological fact (sodium is the primary extracellular cation responsible for osmotic balance, action potentials, and cellular homeostasis). Under the instructions, statements that are trivially true by direct everyday observation and basic biological definitions are classified as common knowledge, requiring no citation.