THE vitamin A or retinol it is a fat-soluble compound found in a wide variety of foods 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 provitamin A activity that act as food precursors to retinol.
Vitamin A is supplied in the diet in the form of preformed vitamin A (retinyl esters) of animal origin or provitamin A of plant origin (carotenoids).
Retinol can be obtained directly from food or be converted in the human body from beta-carotene.
About 90% of vitamin A is stored in the liver as retinyl esters. It can also be deposited in the eyes and lungs.
In the retina, 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
You animal foods that are sources of vitamin A are:
- fish oils;
- Meat;
- Liver;
- Butter;
- Egg yolk;
- Whole milk and cheeses.
You plant foods that are sources of vitamin A are:
- Carrots, tomatoes, peppers;
- 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 proper functioning of vision, growth and development, division cell, gene expression, maintenance of epithelial cell integrity, immune function and defense antioxidant.
Some of its benefits are:
- Helps in good eyesight;
- Antioxidant effect preventing the onset 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, is the lack of vision in dimly lit environments, since the vitamin A participates in the formation of rhodopsin, a pigment found in the retina and responsible for vision in the dimness.
Vitamin A deficiency also influences the iron metabolism, decreasing its incorporation into red blood cells.
Another extremely important element that influences vitamin A metabolism is zinc.
Zinc deficiency can interfere with the transport of vitamin A, by reducing the production of the transporter protein. As well as the conversion of retinol to retinal, which requires the action of zinc-dependent retinol dehydrogenase.
Learn more and also read about:
- Vitamins
- Nutrients
Hypervitaminosis
Excess vitamin A, more than 100 mg daily, can cause anorexia, vomiting, headache, bone lesions painful, accelerated bone growth, lack of muscle coordination, desquamative dermatitis and hepatotoxicity.
In more chronic cases, changes in hair, loss of eyelashes, dryness and the appearance of cracks in the skin, especially on the lips, can also be observed.
Read too:
- Vitamin K
- Vitamin C
- Healthy eating
