Surfeit and Deficit of Sodium

Normal man can maintain an over-all sodium balance at intakes varying from a few to 1000 mEq. or more of sodium daily. Although this balance is customarily referred to as a steady state, at all levels of sodium intake higher than a few milliequivalents daily it represents in reality a constantly fluctuating level of total body sodium. Each time sodium is ingested a positive balance is produced which is steadily reduced in the following hours by way of renal sodium excretion. This is well illustrated in a study from this laboratory¹in which identical meals and quantities of salt were administered to constantly recumbent subjects at six-hour intervals. Figure 1, plotted for the second day of this study, reveals that the sodium ingested at the beginning of each six-hour period has just about been eliminated by the end of the period, save for the night hours, particularly from midnight