Effects of oral loads of sodium chloride on bone composition in growing rats consuming ample dietary calcium

High dietary intakes of sodium chloride and protein are known to promote urinary calcium excretion. The aim of this work was to study the effects of bone composition, calcium balance and phosphorus balance, of administering oral salt supplements (8 g/100 g diet) to growing rats consuming moderate or high dietary levels of protein (25 and 60% casein) with ample calcium (0.6% Ca) and adequate vitamin D. Animals given salt supplements excreted more calcium and phosphate in their urine and had less calcium and phosphate in their bones than controls which did not receive supplementary salt. However, salt-loaded rats did not increase their intestinal absorption of calcium to compensate for urinary losses of calcium. Calciuria was greater at the high, than at the moderate, protein intake. Salt supplements raised urinary cyclic AMP and urinary hydroxyproline in rats consuming 25% casein but not in those receiving 60% casein. It is concluded that high dietary intakes of sodium chloride depress the accumulation of mineral in bone; the effect is attributed to increased excretion of calcium and phosphate. These findings raise the possibility that a high salt intake may adversely affect bone mass in man.