Vitamin A (retinol)
For the first time vitamin A has been isolated from carrots, so the British carrot (carrot), there was a name of vitamin A - the carotenoids. Carotenoids found in plants, some fungi and algae, and when ingested can turn into vitamin A. These include a, b and d-carotene, lutein, lycopene, zeaxanthin. Best known of the order of five hundred carotenoids.
The most well-known carotenoid is b-carotene. He is a provitamin of vitamin A (in the liver it is converted into vitamin A as a result of oxidative cleavage).
Activity of vitamin A is measured in units called retinol equivalents.
An ER (retinol equivalent) = 1 mcg retinol = 6 mg b-carotene. 1 mg = 3.33 IU (international units)
3.33 IU vitamin A activity from retinol
10 IU of vitamin A activity of b-carotene
Sources of animals
Cod liver oil, liver (especially beef), eggs, milk, butter, margarine, sour cream, cottage cheese, egg yolk.
Sources of vegetable
Green and yellow vegetables (carrots, squash peppers, spinach, broccoli, green onions, parsley), legumes (soybeans, peas), peaches, apricots, apples, grapes, watermelon, melon, rose, buckthorn, black cherry, herbs (alfalfa , borage leaves, burdock root, cayenne pepper, fennel, hops, horsetail, kelp, lemongrass, mullein, nettle, oats, parsley, peppermint, plantain, raspberry leaves, clover, rose hips, sage, bearberry, violet leaves, sorrel) .
Synthesis in the body
Formed by oxidative cleavage of b-carotene
Recent studies have shown that none of the plant or animal products can not compensate for a deficiency of vitamin A, therefore, a need to supplementation (WHO Bulletin, 1999).
Properties
Vitamin A is involved in redox processes, regulation of protein synthesis, promotes normal metabolism, the functions of cellular and subcellular membranes and plays an important role in the formation of bones and teeth, as well as fat, is essential for growth of new cells, slows the aging process.
Is essential for photoreception provides normal operation of the visual analyzer, is involved in the synthesis of visual pigment retina eye and perception of light.
Vitamin A is essential for the normal functioning of the immune system and is an integral part of infection control. Application of retinol enhances the barrier function of mucous membranes, increases the phagocytic activity of leucocytes and other factors of nonspecific immunity. Vitamin A protects against colds, flu and respiratory infections, digestive tract, urinary tract infections. The presence in blood of vitamin A is one of the main factors responsible for the fact that children in more developed countries is much easier to tolerate such infectious diseases as measles, chicken pox, while in countries with low living standards are much higher death rate from these "harmless" virus infections. Vitamin A prolongs life, even AIDS.
Retinol is essential for the maintenance and restoration of epithelial tissues, which make up the skin and mucous membranes. No wonder almost all modern cosmetics contain retinoids - its synthetic analogues. Indeed, vitamin A is used to treat virtually all skin conditions (acne, acne, psoriasis, etc.). Skin lesions (wounds, sunburn) vitamin A accelerates the healing process and stimulates collagen synthesis, improves the quality of the newly formed tissue and reduces the risk of infections.
Because of its close association with mucous membranes and epithelial cells of vitamin A beneficial effect on the functioning of the lungs and is a worthy complement to the treatment of certain diseases of the gastrointestinal tract (ulcers, colitis).
Retinol is essential for normal embryonic development, nutrition, the fetus and reduce the risk of pregnancy complications such as low birth weight.
Vitamin A is involved in the synthesis of steroid hormones (including progesterone), spermatogenesis, is an antagonist of thyroxine - a hormone the thyroid gland.
As vitamin A and b-carotene, being powerful antioxidants, are a means of prevention and treatment of cancer, in particular, preventing the re-emergence of the tumor after surgery.
Antioxidant action of b-carotene plays an important role in preventing heart disease and arteries, it has a protective effect in patients with angina and increases blood levels of "good" cholesterol (HDL).
Yet another carotenoid - lycopene (found in a core in tomatoes) protects against atherosclerosis by preventing oxidation and the accumulation of cholesterol in the arteries of low density. In addition, it is the "strong" carotenoids in protection against cancer, particularly breast cancer, endometrial and prostate cancers.
Daily maintenance
Average adult should consume daily about 3300 IU of vitamin A. In diseases associated with deficiency of retinol, dosage may be increased to 10000 IU per day.
Pregnant women - up to 1000 IU per day.
With increasing temperature and increasing exposure to sunlight (eg during summer vacation in the south) requirement for vitamin A increases dramatically.
Also reduced supplies of vitamin A in the liver, and, consequently, increases the need for an x-ray.
In women taking oral contraceptives, the need for vitamin A drops (Multivitamin supplementation in oral contraceptive users. Mooij PN et al. Contraception 1991 Sep; 44 (3) :277-88).
Hypovitaminosis
Vitamin A deficiency is defined as the content of retinol in blood serum below 0.35 micromoles / liter. However, even at the level of plasma 0,70-1,22 mmol / l may be a significant reduction in vitamin A in the liver, where it accumulates. Vitamin A levels in the plasma begins to decline when its concentration in liver drops to 0.7 umol / g tissue.
Reasons:
lack of vitamin A in food, especially in the winter-spring period;
unbalanced diet (lack of long-term high-grade proteins violates the assimilation of vitamin A);
limiting consumption of fats (vitamin A is fat-soluble);
liver and biliary tract;
diseases of the pancreas, intestine;
significant small bowel resection, malabsorption syndrome;
inadequate intake of vitamin E (vitamin E, as antioxidant, prevents oxidation of vitamin A).
Clinic:
Early aging of the skin to form wrinkles
Dandruff
Increased pain and temperature sensitivity
Increased sensitivity of tooth enamel
Watery eyes in the cold
The accumulation of crusts and mucus in the corners of the eyes, the feeling of "sand" in the eyes, redness of eyelids
Weakened erections, rapid ejaculation, weak urinary sphincter, etc.
The most well known symptom of hypovitaminosis A is the so-called "night blindness (night blindness or day-blindness) - a sharp deterioration in vision in low light.
Vitamin A deficiency leads to changes in almost all organs and body systems:
corneal opacity, xerophthalmia (dryness of the mucous membrane-eye), itchy eyes in the cold, the accumulation of crusts and mucus in the corners of the eyes, the feeling of "sand" in the eyes, redness of the eyelids, xanthelasma century;
dry skin, premature aging of skin to form wrinkles, seborreyny dermatitis, acne, precancerous diseases and skin cancer;
dry hair, dandruff;
hyperesthesia of tooth enamel;
atrophic gastritis, colitis, cholelithiasis, diarrhea, intestinal infections, cancer of the pancreas, liver cysts;
weakness of the sphincter of the bladder, erectile dysfunction, decreased libido;
cervical erosion, endocervicitis, polyps, adenomatosis, leukoplakia;
breast cancer, breast cancer;
respiratory infections, sinusitis, pneumonia, frequent colds, chronic bronchitis, bronchiectasis, lung cancer;
anemia;
cellular immunodeficiency;
developmental disorders, stunted growth;
increased pain and temperature sensitivity;
insomnia, exhaustion.
