Vitamin A is a light - yellow crystalline compound, also known as retinol - a name given in connection with the participation of this compound in the function of the retina of the eye. Vitamin A is also called the "anti-infective" vitamin because of its role in supporting the immune system.
While retinol is contained only in foods of animal origin, fruits and vegetables contain carotenoids that also have vitamin A activity. The body has the ability to convert some carotenoids, including beta carotene, alpha-carotene and gamma-carotene into vitamin A. These are called carotenoids provitamin A compounds.
Vitamin A Functions
- Support the vision - human retina contains four types photo pigments that store vitamin A compounds. One of these pigments is called rhodopsin, located in the cells of the retina. It allows these cells to detect small amounts of light, and thus plays a major role in the adaptation of the eye to its surrounding conditions and night vision.
- Support the Immune System - Vitamin A boosts the immune system by boosting growth and preventing stress-induced shrinkage of the thymus gland. Vitamin A also improves the function of white blood cells with anti-viral activity.
- Support for cell growth - Vitamin A is also necessary for normal cell growth and development.
- Other functions of vitamin A
Vitamin A is important for the reproductive processes of men and women and plays a role in normal bone metabolism. In addition, it is considered that vitamin A (in the form of retinoic acid) plays an important role in the regulation of genetic events.
Vitamin A Deficiency
Nutritional vitamin A deficiency is quite common in developing countries and is associated with a high incidence of blindness, viral infections, and infant mortality. Vitamin A deficiency primarily affects the health of skin, hair, eyes and immune system, although loss of appetite, bone abnormalities, and growth retardation have also been associated with insufficient intake of this vitamin.
Vitamin A Overdose
Vitamin A can cause side effects when taken in excessive quantities. The toxicity of vitamin A due to accidental ingestion of doses above 200 mg retinol and 100 mg retinol for adults and children, respectively, can cause adverse reactions. Effects associated with its toxicity are usually temporary and include loss of appetite, irritability, fatigue, weakness and vomiting.
The National Academy of Sciences of the United States has set the upper limit for intake of retinol, as follows:
- Children 3 years or less, 600 micrograms per day
- Children 4-8 years, 900 micrograms
- Children 9-14 years 1, 700 micrograms
- Teens 14-18 years, 2, 800 micrograms
- Adults 19 years and older, 3, 000 micrograms
- Pregnant or lactating women 18 years or younger, 2800 micrograms
- Pregnant or lactating women, 19 years or older, 3, 000 micrograms
Because vitamin A is fat-soluble, its deficiency can be caused by a diet that is extremely low in fat and the presence of medical conditions that lead to reduced ability to absorb dietary fat.
Drugs that affect the absorption, utilization and excretion of vitamin A are: PHARMACEUTICALs that lead to lower cholesterol, bile acid isolation, contraceptive Medroxyprogesterone, Neomycin and others.
Vitamin A Benefits
Vitamin A may play a role in the prevention and treatment of the following diseases: acne, AIDS, alcoholism, atopic dermatitis, cataracts, cervical dysplasia, diabetes, breast disease, Kaposi's sarcoma, osteoarthritis , ear infection, poor vision, psoriasis, disorders thyroid, ulcer, viral infections and others.
As a dietary supplement Vitamin A is available in the form of retinol. Retinoic acid is a form of vitamin A, which is contained in drugs for the treatment of skin diseases.
Calf liver is an excellent source of vitamin A, while milk and eggs are identified as good sources. Plant foods that contain carotenoids are also sources of vitamin A.