Which statement best describes the roles of calcium and vitamin D in bone health?

• A. Osteoporosis risk is unaffected by calcium intake.
• B. Vitamin D stores calcium in bones; calcium is not involved in absorption.
• C. Calcium provides bone structure; vitamin D enhances calcium absorption and bone mineralization.
• D. Calcium supplies energy for bone remodeling.

Answer: (C)

Calcium provides bone structure; vitamin D enhances calcium absorption and bone mineralization. Calcium is the main mineral in the bone matrix, giving bones their rigidity and serving as a reservoir for bodily calcium. Vitamin D, especially in its active form calcitriol, increases calcium (and phosphate) absorption from the gut and supports the mineralization of the bone by ensuring these minerals are available at the site of bone formation. Without adequate vitamin D, calcium absorption is impaired, which can lead to weaker bones and higher fracture risk. Remodeling relies on mineral availability and cellular activity, not on calcium supplying energy. The other statements misstate calcium’s role or vitamin D’s function, whereas the described interaction best captures how calcium provides structure and how vitamin D optimizes its use for bone health.