How much calcium can an adult absorb from a single 500-mg dose?

• A. About 300 mg
• B. About 150 mg
• C. About 200 mg
• D. About 500 mg

Answer: (C)

The human body has a limit to the amount of calcium that can be effectively absorbed in a single dose, which is influenced by various factors including the body's physiological state, the source of calcium, and the presence of other nutrients. For adults, research indicates that the typical absorption efficiency from a dose typically peaks around 200-300 mg, with many studies suggesting that approximately 200 mg is a more realistic figure for a 500-mg dose of calcium, particularly from supplements.

This limited absorption reflects the body's regulatory mechanisms designed to maintain calcium homeostasis. When calcium is consumed in larger amounts, such as a 500-mg dose, the intestines tend to absorb a fixed percentage of the intake, and the excess may pass through the body unabsorbed. Therefore, the correct answer aligns with the physiological understanding of calcium absorption efficiency.