Abstract
Blood concentration of vitamin A (VA), which is present as different molecules, i.e., mainly retinol and provitamin A carotenoids, plus retinyl esters in the postprandial period after a VA-containing meal, is affected by numerous factors: dietary VA intake, VA absorption efficiency, efficiency of provitamin A carotenoid conversion to VA, VA tissue uptake, etc. Most of these factors are in turn modulated by genetic variations in genes encoding proteins involved in VA metabolism. Genome-wide association studies (GWAS) and candidate gene association studies have identified single nucleotide polymorphisms (SNPs) associated with blood concentrations of retinol and β-carotene, as well as with β-carotene bioavailability. These genetic variations likely explain, at least in part, interindividual variability in VA status and in VA bioavailability. However, much work remains to be done to identify all of the SNPs involved in VA status and bioavailability and to assess the possible involvement of other kinds of genetic variations, e.g., copy number variants and insertions/deletions, in these phenotypes. Yet, the potential usefulness of this area of research is exciting regarding the proposition of more personalized dietary recommendations in VA, particularly in populations at risk of VA deficiency.
Highlights
The term vitamin A (VA) is employed generically for all derivatives of β-ionone that possess the biological activity of all-trans retinol (RET) or are closely related to it structurally [1]
retinyl palmitate (RP) and βC, areofassumed to secreted in these two pathways is not known, but we suggest that it depends on the relative activities be mostly secreted in chylomicrons, while the less apolar forms, i.e., RET [48], retinoic acid and of the enterocyte enzymes involved in VA metabolism
The relative proportion of VA secreted in these two pathways is not known, but we suggest that it depends on the relative activities of the enterocyte enzymes involved in VA metabolism
Summary
The term vitamin A (VA) is employed generically for all derivatives of β-ionone (other than the carotenoids) that possess the biological activity of all-trans retinol (RET) or are closely related to it structurally [1]. A recent analysis of the results of 11 studies in eight developed countries (representing ≈ 120,000 participants) has shown that preformed VA intake accounted for about 65% of total VA intake, while provitamin A carotenoids represented 35% of total VA intake (βC: 86%; α-carotene: 10%; β-cryptoxanthin: 4% thereof, respectively) [13] Both preformed VA and proVA carotenoids can be metabolized to the three main active VA molecules recovered in the human body, i.e., RET, retinal and retinoic acid, the metabolic pathways by which each form of VA is metabolized are partly different until they are converted to retinal. The review finishes by listing the points to focus on in the forthcoming years to identify the main genetic variations that are involved in these phenotypes
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