Which of the following best describes a calcium metabolism consequence of immobility?

• A. Increased calcium absorption
• B. No change in calcium absorption
• C. Decreased parathyroid hormone activity
• D. Calcium absorption is impaired, leading to bone loss

Answer: (D)

Lack of weight-bearing activity reduces the stimulus that bones need to stay mineralized. When the skeleton isn’t loaded, bone remodeling shifts toward resorption, with osteoclasts breaking down bone and releasing calcium into the bloodstream. The body tries to maintain normal serum calcium, often by increasing parathyroid hormone, which further promotes bone resorption. Over time this calcium mobilization from bone leads to bone loss and lower bone density. The statement that calcium absorption is impaired captures the idea that calcium availability for bone maintenance is reduced, contributing to bone loss, even though the primary mechanism in immobility is increased bone resorption rather than a direct drop in gut calcium absorption. The other options describe effects that don’t fit the way immobility alters calcium balance and bone turnover.