Which protein transports retinol (Vitamin A) in the blood?

• A. Retinol Binding Protein for Vitamin A
• B. Transthyretin for T4
• C. Albumin
• D. Transferrin for iron

Answer: (A)

Retinol-binding protein is the specific carrier that binds retinol and carries it in the bloodstream. Produced by the liver, it binds retinol to form a complex that travels through plasma. To prevent loss in the kidneys and to extend circulation time, this complex often associates with transthyretin, but the primary transporter for retinol itself is the retinol-binding protein.

Transthyretin mainly carries thyroid hormone (T4) and, when associated with the retinol complex, helps stabilize it rather than serving as the primary retinol carrier. Albumin handles many different ligands non-specifically, but retinol transport is principally via retinol-binding protein. Transferrin’s role is to transport iron.