STIMULATION BY CITRIC-ACID OF CALCIUM AND PHOSPHORUS BIOAVAILABILITY IN RATS FED A CALCIUM-RICH DIET

The effect of dietary citric acid supplementation on calcium (Ca) and phosphorus (P) bioavailability was studied in rats fed 3 different die ts containing 0.1, 0.5 or 1.0 g/1.00 g Ca during 7 weeks. Citric acid supplementation increased intestinal Ca and P absorption and the Ca an d P retention/intake ratio only in rats fed the 1% Ca diet. It also in creased the P concentration of bone ashes in rats fed the 0.5% Ca diet (18.9 +/- 0.2 vs. 17.5 +/- 0.5%) and the 1% Ca diet (20 +/- 0.1 vs. 1 9 +/- 0.3%), and the Ca bone ash concentration in rats fed the 1% Ca d iet (36.7 +/- 0.4 vs. 35.7 +/- 0.5%). In rats fed the 1% Ca diet, plas ma P concentration was decreased by citric acid supplementation (2.09 +/- 0.10 vs. 2.45 +/- 0.08 mmol/l) while urinary P excretion was incre ased (18.2 +/- 2.3 vs. 2.0 +/- 0.3 mmol/4 days), together with a decre ase in plasma calcitriol concentration (54.4 +/- 2.6 vs. 79.6 +/- 2.5 ng/l), but no change of the circulating parathyroid hormone level. Thi s study indicates that citric acid supplementation together with a Ca- rich diet allows to obtain an increased retention of Ca and P in bone. The prolonged administration of Ca citrate supplements may therefore help to increase bone mineral concentration.