Intestinal calcium absorption is mainly controlled by the serum concentration of which substance?

Correct option is D

• 1,25-dihydroxy vitamin D (calcitriol) is the active hormonal form of vitamin D and is the primary regulator of intestinal calcium absorption.
• It increases synthesis of calcium-binding proteins in intestinal cells, allowing efficient uptake of dietary calcium.
• When calcitriol levels rise, calcium absorption increases; when levels fall, absorption decreases.
• Albumin binds calcium in blood but does not regulate absorption.
• Triglycerides have no role in calcium metabolism.
• Ferritin reflects iron stores and is unrelated to calcium absorption.