Control of calcium absorption: effect of sodium chloride loading and depletion.

In six out of eight patients with normal parathyroid function and in two subjects with hypoparathyroidism, sodium chloride loading was shown to increase calcium absorption as measured by the 47Ca absorption test. Although no significant change was seen in the renal and fecal excretion of calcium, a slight decrease in total serum calcium did occur with increased sodium intake. The change in calcium absorption was not accompanied by a detectable change in calcium balance. Therefore, a compensatory change in gastrointestinal calcium secretion must have occurred. Sodium intake has an effect on calcium in the gastrointestinal tract, which is independent of parathyroid hormone. Sodium intake should be considered when results of studies of calcium metabolism are compared.