Levels of Vitamin A (beta carotene)

Vitamin A is an umbrella term for several fat-soluble substances such as retinol, retinyl palmitate and beta-carotene. Its various metabolites are essential for vision, cell differentiation, epithelial barrier function and immune function.

Vitamin A is an essential micronutrient that plays an important role in a wide range of physiological processes, including vision, immune response, cell differentiation and proliferation, intercellular communication and reproduction.It is a term that collectively encompasses retinol and its active metabolites, including retinal, retinyl ester and retinoic acid.

Vitamin A is obtained through the diet in two forms, since we cannot synthesize this vitamin. Preformed vitamin A (retinol and retinyl ester) is obtained from animal sources such as meat, dairy products and fish. Provitamin A (beta-carotenoid) is obtained from colored fruits and vegetables. Both forms of ingested vitamin A must be converted to retinal and retinoic acid after absorption to support biological processes.

Beta-carotenoids and carotenoids in general act as antioxidant substances that protect the body against reactive oxygen species or ROS and play an important role in the prevention of multiple conditions, including cardiovascular disease and diabetes. Studies suggest that carotenes have a protective effect on non-alcoholic fatty liver disease and lung cancer.

Vitamin A deficiency replaces normal epithelium with stratified, keratinizing epithelium in the eyes, periocular glands, respiratory tract, alimentary tract and genitourinary tract. Excess vitamin A causes acute and chronic adverse health effects.

Vitamin A deficiency is much more common worldwide than vitamin A toxicity. The World Health Organization (WHO) estimates that 3 million children develop clinical vitamin A deficiency annually, compared to the estimated 200 cases of vitamin A toxicity diagnosed annually.

The formation of vitamin A from provitamin A depends on the efficiency of absorption and the efficiency of conversion of the major active metabolites of vitamin A such as retinal, retinol and retinoic acid. Interindividual differences in the absorption and conversion of carotenoids to the biologically active forms of vitamin A have been observed, and studies suggest that certain single nucleotide polymorphisms in genes encoding enzymes involved in the absorption and conversion of beta-carotene may explain some of this variability.

Circulating levels of β-carotene are influenced by gender, as well as autosomal genetic variations and fruit intake. The β-carotene, which is a provitamin, is transformed into the various active forms of vitamin A, such as retinol, retinal and retinoic acid.

Several genome-wide association studies have identified the same marker associated with circulating carotenoid levels, using populations of different origins. This marker is found in the BCMO1 gene that produces the enzyme beta-carotene 15,15′-monooxygenase, which is involved in the transformation of beta-carotene into active vitamin A metabolites, identifying those individuals carrying the marker as possible "poor converters", given that the efficiency in the transformation would be lower, by producing less quantity of the enzyme or that this has a reduced functional activity, accumulating a greater quantity of beta-carotene.

These results can only be applied to the transformation capacity of beta-carotene into active metabolites of vitamin A and not to the total levels of vitamin A, given that not only precursors such as beta-carotene, but also active forms such as retinol, can be accessed through the diet.

The effect of the marker studied may be especially important in individuals at high risk for vitamin A deficiency; these include individuals with cystic fibrosis and malabsorption syndromes and preschool children in developing countries.

Number of observed variants

13.5 million variants

Number of variants analyzed in the study

1 variant

Bibliography

Borel P. et Desmarchelier C. Genetic Variations Associated with Vitamin A Status and Vitamin A Bioavailability. Nutrients. 2017 Mar; 9(3): 246.

Ferrucci L., Perry J.R.B., et al. Common Variation in the ?-Carotene 15,15?-Monooxygenase 1 Gene Affects Circulating Levels of Carotenoids: A Genome-wide Association Study. Am J Hum Genet. 2009 Feb 13; 84(2): 123–133.

Yabuta H., Urata M.., et al. Common SNP rs6564851 in the BCO1 Gene Affects the Circulating Levels of ?-Carotene and the Daily Intake of Carotenoids in Healthy Japanese WomenPLoS One. 2016; 11(12): e0168857.

Chea E.P., Lopez M.J., et al. (2021) Vitamin A. StatPearls

Debelo H., Novotny J.A. et al. (2017) Vitamin A. Adv Nutr. 2017 Nov; 8(6): 992–994.

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