Calcium supplements and milk: effects on acid-base balance and on retention of calcium, magnesium, and phosphorus.

The effect of supplementing a basal diet containing 697 mg calcium daily (17.4 mmol/d) with an additional 900 mg Ca daily from milk, Ca chloride, or a Ca carbonate preparation was examined in eight adult males during a 56-d metabolic balance study. The ingestion of the milk or Ca supplements had no overall effect on Ca retention by these subjects because the milk and supplements depressed apparent absorption of Ca in the gut and fractional tubular reabsorption of Ca in the kidneys. Supplementation of the diet with CaCl and to a lesser extent with milk significantly increased renal acid excretion whereas supplementation with CaCO3 depressed renal acid excretion. The three Ca supplements significantly altered magnesium and phosphorus absorption and urinary excretion in different manners but had no overall effect on retention of P or Mg. The responses of our subjects to these treatments may be different than those of subjects who are chronically in negative balance in regard to Ca.