provitamin a
Học thuậtThân thiện
Definition
Noun: A substance, specifically an orange isomer of an unsaturated hydrocarbon, that is found in many plants. The body converts this substance into vitamin A within the liver. It is a precursor to vitamin A.
Usage
The term "provitamin A" is used in nutritional and biochemical contexts to refer to plant-derived compounds that can be transformed by the body into active vitamin A (retinol). The most common example is beta-carotene.
Examples
- Carrots are a rich source of provitamin A.
- The human body's ability to convert provitamin A into retinol varies from person to person.
- Scientists measured the provitamin A content in various leafy green vegetables.
Advanced Usage
- Biochemical Context: In biochemistry, "provitamin A" refers specifically to carotenoids like alpha-carotene, beta-carotene, and beta-cryptoxanthin, which possess the structural activity to be converted into retinol.
- Nutritional Labeling: On food or supplement labels, the vitamin A activity from provitamin A carotenoids is often expressed in Retinol Activity Equivalents (RAEs) to account for the conversion efficiency.
Variants and Related Words
- Beta-carotene (n): The most common and efficient provitamin A carotenoid found in plants.
- Carotenoid (n): A class of pigments to which provitamin A compounds belong.
- Precursor (n): A more general term for a substance from which another, usually more active, substance is formed.
Synonyms
- Vitamin A precursor
- Carotenoid precursor (when referring specifically to carotenoid forms)
Antonyms
- Preformed vitamin A (also called retinol): The active form of vitamin A found in animal products, which does not require conversion.
Related Phrases/Compounds
- Provitamin A carotenoid: A more precise term specifying the class of compounds.
- Vitamin A activity: A measure that includes contributions from both preformed vitamin A and converted provitamin A.
Noun
- an orange isomer of an unsaturated hydrocarbon found in many plants; is converted into vitamin A in the liver