Lactose and potassium are also thought to move from the milk space to the blood. the net result is that under these conditions,milk has greatly increased concentrations of sodium and chloride and decreased concentrations of lactose and potassium. the presence of high sodium concentrations in human milk is diagnostic of either mastitis or low milk-volume secretion.Colostrum has much higher concentrations of sodium and chloride than does mature milk because the gland is undergoing the transition between pregnancy,when the junction are open,and full lactation,when they are closed. Preterm milk shows lower concentration of sodium and chloride that rise to normal levels approximately 30 day postpartum.