Solubility and intestinal transit time limit calcium absorption in rats

Area of Science:

• Nutritional Science
• Gastroenterology
• Biochemistry

Background:

• Dietary calcium intake is crucial for bone health and physiological functions.
• Understanding calcium absorption mechanisms is vital for optimizing nutritional strategies.
• Different calcium compounds may influence bioavailability and absorption rates.

Purpose of the Study:

• To compare the effects of calcium carbonate and calcium gluconate on calcium absorption in rats.
• To investigate how varying calcium intake levels impact absorption efficiency.
• To elucidate the role of luminal factors in differential calcium absorption.

Main Methods:

• Rats were fed high-calcium diets with either calcium carbonate or calcium gluconate as the primary source.
• Calcium absorption was measured across a range of dietary calcium intakes.
• Active and nonsaturable calcium transport mechanisms were analyzed.

Main Results:

• Animals fed calcium gluconate absorbed 29% of ingested calcium, while those on calcium carbonate absorbed 25% at lower intakes.
• Calcium carbonate absorption plateaued at high intakes (above 450 mg Ca/d), reaching approximately 109 mg/d.
• Active calcium transport decreased with increased intake for both groups; nonsaturable transport remained constant.

Conclusions:

• Calcium source significantly impacts absorption, with calcium gluconate demonstrating higher overall bioavailability.
• Limited calcium absorption from calcium carbonate at high intakes is attributed to reduced solubilization in the presence of phosphate.
• Solubility of calcium in the intestinal lumen is a key determinant of absorption efficiency.