Vitamin A and β-carotene

Vitamin A, or retinol, is an essential nutrient for man and all mammalian species since it cannot be synthesised within the body. Deficiency of the vitamin results in adverse effects on growth, reproduction and resistance to infection.

Vitamin A occurs as retinyl esters in foods of animal origin and in the form of provitamin A carotenoids in plant foods. Some carotenoids found in colourful fruits and vegetables are called provitamin A; they are metabolized in the body to vitamin A.

Among the carotenoids, β-carotene, a retinol dimer, has the most significant provitamin A activity in human nutrition, since its concentration in food and feed ingredients, particularly of leaf origin, greatly exceeds that of the other vitamin A active compounds. Other provitamin A carotenoids, such as α-carotene and β-cryptoxanthin, are half as active as β-carotene.

The β-carotene molecule contains two β-ionic rings. Theoretically the cleavage of that chain at –C15 = C15′– position provides two retinol molecules.

Carotenoids play a prominent role in protecting bodily cells and thereby act as powerful antioxidants. It has been observed that carotenoid pigments in all photosynthetic organisms, bacteria, algae, and higher plants, play an important role in protecting these organisms against the seriously damaging effects of photooxidation by their own endogenous photo-sensitizer, chlorophyll.

Due to its high bioactivity, β-carotene is also widely used in medicine. Among the numerous functions of β-carotene in the human body, the important one is related to provitamin A supply, further affecting embryonic development, correct growth, and sight. It is considered as an inhibitor of some genes; moreover, it exhibits anticancer and antioxidant properties.
Vitamin A and β-carotene

Carotene in carrot

Carrot juice has a number of health benefits. The carrot provides what is certainly the most important basic juice. Carrot roots are a rich source of carotenoids. The total carotenoid content in the edible portion of carrot roots ranges from 6000 to 54800 μg/100 g.

The predominant carotenoids in orange-colored carrots are β-carotene, α-carotene and γ-carotene. The proportion of individual pigments reported includes β-carotene (45-80%), α-carotene (15-40%), γ-carotene (2-10%), and others (3-6%). Another name for this form of carotene, the transform, is pro vitamin A.

Many authors write that carrots contain a lot of vitamin A. This is not actually true; what the carrot does contain is the pro vitamin. That means a substance that is converted by the body into the vitamin itself.

Β-carotene is converted to vitamin A on the body. Because of differences in uptake, storage and chemical processing, only about one-sixth of the β-carotene in a plant food ends up as vitamin A in the body.
Carotene in carrot

Roles of vitamin A in human body

Vitamin A -active compounds, defined as compounds having qualitatively the biological activity of retinal, are represented by retinoid and pro-vitamin A carotenoids.

Vitamin A is required for several essential life processes, including metabolism, haematopoeisis, bone development, pattern formation during embryogenesis, the maintenance of differentiated epithelia, and immune-competence.

These processes can be supported by all forms of vitamin A, including the pro-vitamin A carotenoids. The other vitamin functions namely in reproduction, growth, the maintenance of skin and mucous membranes and the visual process, require either retinol or retinaldehyde.

Retinol

Vitamin A is needed to process incoming light to visual images and to keep the eye’s surface healthy. Moreover, beta-carotene –a compound that the body converts to vitamin A - is an antioxidant and thus works to neutralize harmful substances known as free radicals.

As such, beta-carotene appears to help protect the body against a variety of disorders, including cancer and heart disease.

Vitamin A is known to be involved in fetal development and in the regulation of proliferation and differentiation of many types of cells throughout life. The effects of vitamin A on cellular differentiation are due to the control of gene expression by retinoic acid in selected tissues, the protein products being responsible for the effects.

It plays a role in immune function, both as a cell regulator and by helping maintain the skin and mucous membranes.
Roles of vitamin A in human body