The vitamin A or retinol is a lipid soluble compound found in a variety of food and with important biological functions.
The term refers to a group of substances that include retinol, retinaldehyde and retinoic acid. In addition to carotenoids, with pro-vitamin A activity that act as food precursors of retinol.
Vitamin A is supplied in the diet in the form of preformed vitamin A (retinyl esters) of animal origin or pro-vitamin A of plant origin (carotenoid).
Retinol can be obtained directly from food or converted into the human body from beta-carotene.
About 90% of vitamin A is stored in the liver in the form of retinyl esters. It can also be deposited in the eyes and lungs.
In the retina, the reversible oxidation of vitamin A produces retinaldehyde, which is an essential constituent of the visual pigment rhodopsin, found in rods.
Foods rich in vitamin A
Animal foods that are sources of vitamin A are:
- Fish oils;
- Meat;
- Liver;
- Butter;
- Egg yolk;
- Whole milk and cheeses.
The plant foods that are sources of vitamin A are:
- Carrot, tomato, pepper;
- Sweet potatoes, broccoli, pumpkin, mango;
- Melon, peach, papaya.
Some exotic fruits are also sources of vitamin A.
What is vitamin A for?
Vitamin A is essential for the proper functioning of vision, growth and development, cell division, gene expression, maintenance of epithelial cell integrity, immune function and antioxidant defense.
Some of its benefits are:
- Assists in good vision;
- Antioxidant effect preventing the appearance of cancer;
- It acts on the development of the fetus during pregnancy.
Hypovitaminosis
The lack of vitamin A in the diet causes diseases such as xerophthalmia and night blindness .
Xerophthalmia is characterized by dryness of the cornea of the eye, causing vision problems and blindness due to scarring from ulcerations.
Night blindness, on the other hand, consists of lack of vision in low light environments, since vitamin A participates in the formation of rhodopsin, a pigment found in the retina and responsible for vision in the dark.
Vitamin A deficiency also influences iron metabolism , decreasing its incorporation into red blood cells.
Another extremely important element that influences the metabolism of vitamin A is zinc.
Zinc deficiency can interfere with the transport of vitamin A, by reducing the production of carrier protein. As in the conversion of retinol to retinal, which requires the action of zinc-dependent retinol dehydrogenase.
Hypervitaminosis
Excess vitamin A, more than 100 mg daily, can cause anorexia, vomiting, headache, painful bone injuries, accelerated bone growth, lack of muscle coordination, scaling dermatitis and hepatotoxicity.
Changes in hair, loss of eyelashes, dryness and the appearance of cracks in the skin, especially in the lips, can also be observed in the most chronic cases.