_A- Vitamins - Beta Carotene
Vitamin A
The structure of retinol, the most common dietary form of vitamin A.
Vitamin A is an essential human nutrient. Vitamin A actually refers to a family of similarly shaped molecules: the retinoids. Its important part is the retinyl group, which can be found in several forms. In foods of animal origin, the major form of vitamin A is an ester, primarily retinyl palmitate, which is converted to an alcohol (retinol) in the small intestine. Vitamin A can also exist as an aldehyde (retinal), or as an acid (retinoic acid). Precursors to the vitamin (provitamins) are present in foods of plant origin as some of the members of the carotenoid family of compounds.
All forms of vitamin A have a Beta-ionone ring to which an isoprenoid chain is attached. This structure is essential for vitamin activity.[1] The orange pigment of carrot - Beta-carotene - can be represented as two connected retinyl groups. The retinyl group, when attached to a specific protein, is the only primary light absorber in visual perception, and the compound name is related to the retina of the eye.
Vitamin A may be found in various forms:
- retinol, the form of vitamin A absorbed when eating animal food sources, is a yellow, fat-soluble, vitamin with importance in vision and bone growth. Since the alcohol form is unstable, the vitamin is usually produced and administered in a form of retinyl acetate or palmitate.
- other retinoids, a class of chemical compounds that are related chemically to vitamin A, are used in medicine.
Vitamin A plays a role in a variety of functions throughout the body, such as:
- Vision - Gene Transcription - Immune Function - Embryonic Development and Reproduction - Bone Metabolism Hematopoiesis - Skin Health - Reducing Risk of Heart Disease and Cancer - Antioxidant Activity.
