Retinol-binding protein half-life is how long?

• A. 12 hours
• B. 24 hours
• C. 2 days
• D. 3 days

Answer: (A)

Retinol-binding protein is a small, liver-derived transporter that carries retinol in the bloodstream and turns over quickly. Its circulating half-life is about 12 hours, reflecting rapid production and clearance to meet the needs of vitamin A transport without long-term reservoirs. This short turnover distinguishes it from other plasma proteins that have longer half-lives, such as transthyretin (around 2 days) and albumin (much longer). Because of this rapid turnover, retinol-binding protein levels can change within a day in response to shifts in vitamin A status or protein-energy status, making 12 hours the best estimate for its half-life.