The effect of low dietary calcium and calcium supplementation on calcium metabolism and bone in the immature, growing rat.

The data presented here were obtained from a series of experiments designed to determine 1) whether normal growth and bone development could be maintained in young, growing rats (3-9 weeks of age) on a diet containing 0.1% Ca, and 2) whether Ca presented in a bolus would be utilized as effectively as the same amount of Ca distributed throughout the diet. Weanling female rats were raised to 9 weeks of age on diets containing 0.4% P and either 0.5% or 0.1% Ca. One group of animals on the 0.1% Ca diet was given oral supplements of CaCO3 twice each day to supply the same amount of Ca consumed by age-matched animals on the 0.5% Ca diet. We found that animals consuming diet containing 0.1% Ca grew at the same rate as animals receiving 0.5% Ca, or 0.1% Ca + supplement for up to 9 weeks of age when the experiment was terminated. Measurement of femur length indicated that long bone length was the same for all animals. However, the 0.1% Ca group exhibited mild hypocalcemia (9.1 mg/dl vs 10.4 for controls), a 2.6-fold elevation in immunoreactive parathyroid hormone, and an increase of similar magnitude in circulating levels of 1,25-dihydroxyvitamin D. Bones from the 0.1% Ca group contained less than half as much Ca as bones from the 0.5% Ca group, and exhibited significant decreases in mid-shaft diaphyseal thickness, % trabecular volume of the distal metaphysis and breaking strength (torsion testing). These results suggest that while a diet containing 0.1% Ca is able to maintain normal growth, bone mineralization is compromised.(ABSTRACT TRUNCATED AT 250 WORDS)