Beta-carotene found in vegetables is converted to Vitamin D in the body.

Question

BlackTom AI · Accepted Answer

Beta-carotene is a provitamin A compound that is enzymatically converted to vitamin A (retinol), not to vitamin D.

1) Relevant knowledge points and concepts
- Beta-carotene: a carotenoid found in colorful vegetables; a provitamin A (precursor of vitamin A).
- Conversion pathway for beta-carotene: cleaved by beta-carotene 15,15'-dioxygenase in the intestinal mucosa or liver to produce retinal, which is reduced to retinol (vitamin A).
- Vitamin D synthesis: derived from 7-dehydrocholesterol in the skin via UV-B radiation (forming previtamin D3, then thermal isomerization to vitamin D3); dietary vitamin D exists as D2 (ergocalciferol) from fungi/plants and D3 (cholecalciferol) from animal sources — not from carotenoids.

2) Step-by-step reasoning
- Identify compound: beta-carotene is chemically a carotenoid with beta-ionone rings; its biochemical role is to provide retinal/retinol.
- Enzymatic step: beta-carotene 15,15'-dioxygenase cleaves beta-carotene centrally → two molecules of retinal.
- Retinal conversion: retinal is enzymatically reduced by retinaldehyde reductase to retinol (vitamin A) or oxidized to retinoic acid (active metabolite).
- Compare with vitamin D pathway: vitamin D originates from cholesterol derivative 7-dehydrocholesterol under UV-B light; there is no metabolic route that converts carotenoids (beta-carotene) into vitamin D.

3) Intermediate steps (biochemical)
- Beta-carotene + O2 —(beta-carotene 15,15'-dioxygenase)—> 2 retinal
- Retinal —(reductase)—> retinol (vitamin A)
- 7-dehydrocholesterol —(UV-B)—> previtamin D3 —(thermal isomerization)—> vitamin D3

4) Why the correct answer is correct
The statement is false because beta-carotene yields vitamin A compounds, while vitamin D is synthesized from a cholesterol derivative under UV-B exposure or obtained from specific dietary sources; biochemical pathways and precursors are distinct.

5) Why the other option is incorrect
The "True" option is incorrect because it asserts a conversion that does not occur biochemically; carotenoids do not serve as precursors for vitamin D.

6) Conclusion
Therefore the correct answer is False, which matches the provided answer.

Beta-carotene found in vegetables is converted to Vitamin D in the body.单项选择题

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