Do healthy very-low-birth-weight infants fed on their own mothers' milk require sodium supplementation?

Sodium and potassium levels were measured weekly in mothers' milk and in serum and urine of 41 supplemented and 25 unsupplemented very-low-birth-weight infants whose mean birth weights were 1390 g and 1332 g, respectively (mean gestational age, 31 weeks). Sodium intake was 5.95 mmol/kg/day for the supplemented group and 2.75 mmol/kg/day for controls, None of the infants in either group was hyponatremic during the 6-week period of study. Urinary sodium in the supplemented group was 15.7 mmol/L as compared with 7.5 mmol/L in controls. Human milk sodium was significantly lower than reported elsewhere. Growth in the supplemented group was greater than in the unsupplemented group. Since no episode of hyponatremia occurred, it was concluded that routine sodium supplementation was unnecessary.