What are the effects of immobility on calcium absorption?

• A. It improves calcium absorption.
• B. It has no effect.
• C. It impairs calcium absorption, leading to disuse osteoporosis.
• D. It increases bone density.

Answer: (C)

Immobilization removes normal mechanical loading from bone, which is a key signal for keeping bone mineral content. Without that stimulus, bone remodeling shifts toward resorption: osteoclasts break down bone and release calcium into the blood, and long-term formation by osteoblasts doesn’t keep up. The result is a loss of bone density—disuse osteoporosis—and the body’s calcium balance becomes impaired as calcium is mobilized from bone rather than being retained in it. Gut calcium absorption is not the primary issue here; the main problem is reduced bone mineral density from increased bone resorption due to lack of mechanical stress.