Interactions between sodium, protein and calcium
Sodium and calcium compete for the same transport mechanism in the kidney, and an excess of one will cause excretion of the other. Protein has a similar effect on urine calcium levels. This interaction is important in the older population because factors that effect urinary calcium, loss are likely to affect bone health: recognition of the interaction allows for the prevention of calcium losses related to high protein intakes.
When diets high in protein, a reduction in sodium intake can reduce the physiological need for calcium and so improve calcium nutrition. Other inhibitors of calcium absorption are phosphates, phytic acid from the husks of cereals, and oxalic acid in spinach and rhubarb, which form insoluble complexes with calcium.