Provitamin A identification Which of the following is a dietary precursor (provitamin) that the human body can convert into vitamin A (retinol)?

Introduction / Context:
Provitamin A carotenoids, particularly beta-carotene, are important contributors to vitamin A nutrition from plant sources. Recognizing which nutrients are precursors versus active vitamins is essential for dietary planning.

Given Data / Assumptions:

• Beta-carotene can be cleaved enzymatically to retinal, which is reduced/oxidized to retinol/retinoic acid.
• Cobalamin (B12), pyridoxine (B6), thiamine (B1), and ascorbic acid (vitamin C) are not precursors of vitamin A.
• Carotenoids are abundant in orange-colored and dark green leafy vegetables.

Concept / Approach:
Select the carotenoid capable of yielding retinoids upon intestinal and hepatic metabolism. Beta-carotene is the canonical example with provitamin A activity.

Step-by-Step Solution:
Identify the compound class with provitamin A activity: carotenoids.Match the specific carotenoid: beta-carotene.Exclude unrelated water-soluble vitamins.

Verification / Alternative check:
Nutrient databases assign retinol activity equivalents (RAE) to beta-carotene intake, reflecting conversion efficiency to vitamin A.

Why Other Options Are Wrong:
Cobalamin, pyridoxine, thiamine, ascorbic acid are distinct vitamins with unrelated functions, not vitamin A precursors.

Common Pitfalls:
Assuming all carotenoids are equal; note that only specific carotenoids (e.g., beta-carotene, alpha-carotene, beta-cryptoxanthin) have provitamin A activity, whereas lutein and zeaxanthin do not.

Final Answer:
Beta-Carotene.