Importance of dietary sodium in the hypercalciuria syndrome.

Daily urinary calcium excretion in renal stone-forming subjects is shown to vary directly with moderate changes in dietary sodium intake. The changes produced are sufficient to alter the basic diagnostic classification from 'hypercalciuric' to 'normocalciuric' because dietary sodium is reduced from 200 to 80 mM/day. Similar changes were observed in fasting morning 'spot' urine samples, resulting in alteration of diagnostic subclassification between so-called 'absorptive' and 'renal' categories, in the absence of demonstrable change in parathyroid function. Diagnostic and therapeutic studies in stone-forming subjects require control of both dietary calcium and dietary sodium if misinterpretations are to be avoided. Habitual high sodium intake may be an etiological factor in the generation of excessive excretion of calcium, sodium, and phosphate--the hypercalciuria syndrome.