Abstract
Vitamin A is essential for life in all vertebrate animals. Vitamin A requirement can be met from dietary preformed vitamin A or provitamin A carotenoids, the most important of which is β-carotene. The metabolism of β-carotene, including its intestinal absorption, accumulation in tissues, and conversion to vitamin A, varies widely across animal species and determines the role that β-carotene plays in meeting vitamin A requirement. This review begins with a brief discussion of vitamin A, with an emphasis on species differences in metabolism. A more detailed discussion of β-carotene follows, with a focus on factors impacting bioavailability and its conversion to vitamin A. Finally, the literature on how animals utilize β-carotene is reviewed individually for several species and classes of animals. We conclude that β-carotene conversion to vitamin A is variable and dependent on a number of factors, which are important to consider in the formulation and assessment of diets. Omnivores and herbivores are more efficient at converting β-carotene to vitamin A than carnivores. Absorption and accumulation of β-carotene in tissues vary with species and are poorly understood. More comparative and mechanistic studies are required in this area to improve the understanding of β-carotene metabolism.
Highlights
Vitamin A (VA) is an essential nutrient for all vertebrate animal species
Hepatic retinol and retinyl ester concentrations were significantly improved in a dose-response manner up to the 23% fat diet, indicating that dietary fat may impact both absorption of BC and its metabolism to VA
These authors showed that the activity of the intestinal BCO enzyme in rats decreased in vivo in a dose-dependent matter with oral doses of retinyl acetate, BC, and retinoic acid and increased with the administration of a RARα receptor antagonist
Summary
Vitamin A (VA) is an essential nutrient for all vertebrate animal species. There are two dietary sources of VA: preformed retinoids and provitamin A (pro-VA) carotenoids. All carotenoids with one or more unsubstituted β-ionone rings can theoretically be VA precursors, β-carotene (BC) appears to be the most important of these. It is certainly the most studied carotenoid, at least in the context of its role as a pro-VA compound. Absorption into blood and accumulation in tissues of intact BC is highly variable and species-dependent.
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