Provitamin A Activity
Plant carotenoids are the primary dietary source of provitamin A worldwide, with β-carotene as the most well-known provitamin A carotenoid. Others include α-carotene and β-cryptoxanthin. Carotenoid absorption is restricted to the duodenum of the small intestine and dependent on Class B scavenger receptor (SR-B1) membrane protein, which are also responsible for the absorption of vitamin E (alpha-tocopherol). One molecule of β-carotene can be cleaved by the intestinal enzyme beta,beta-carotene 15,15'-monooxygenase into two molecules of vitamin A.
Absorption efficiency is estimated to be between 9–22%. The absorption and conversion of carotenoids may depend on the form that the β-carotene is in (e.g., cooked vs. raw vegetables, or in a supplement), the intake of fats and oils at the same time, and the current stores of vitamin A and β-carotene in the body. Researchers list the following factors that determine the provitamin A activity of carotenoids:
- Species of carotenoid
- Molecular linkage
- Amount in the meal
- Matrix properties
- Effectors
- Nutrient status
- Genetics
- Host specificity
- Interactions between factors
Read more about this topic: beta-Carotene
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