Enerex.ca | VITAMIN A

VITAMIN A (Beta-Carotene, Retinol)

General - oil-soluble; anti-xerophthalmic factor;

Retinol (true vitamin A) - found in animal tissues;
Beta-carotene (pro-vitamin A) - yellow-orange pigment of plants;
Conversion of beta-carotene to vitamin A in animal tissues takes 6 to 7 hours & occurs only according to need, making carotene non-toxic;
History: identified in 1913; structure defined in 1931 (Karrer) for Nobel Prize; synthesis 1946; identified as major source of infant mortality in Indonesia 1984;

Nutrition

Sources: vitamin A: liver, egg yolk, fish (esp. fish liver oils), dairy cream & other animal products; lemon grass; beta carotene: carrots, yams, squash, apricots, red & dark green vegetables;
Supplements: A + D, beta carotene, multi-vitamin, multi-mineral-vitamin formulations;
Absorption: from upper small intestine, along with fats, takes about 3 to 5 hours; - vitamin A absorption is 2 to 4x more efficient than that of beta carotene, independent of amount present; toxicity possible for vitamin A; 10 to 50% of carotene is absorbed; absorption decreases if more is present in body;
Improved by: edible fats & oils; taking with meals; vitamin E; bile salts;
Antagonized by: excess protein, alcohol, iron, mineral oil, intense physical activity within 4 hours of ingestion, inflammatory bowel disease;
Stability: vitamin A is destroyed by oxygen in the presence of sunlight; protected by vitamin E; carotene is stable during cooking, but also sensitive to oxygen & light; freezing protects vitamin A and carotene from deterioration;
Storage: 90% of vitamin A in liver (1 to 2 years’ supply = 500,000 IU); high concentrations in kidneys & lungs; some present in all cells; carotene stored in liver, fat tissue, & skin;
Antagonized by: cirrhosis & liver degeneration;
Excretion: through bile, through urine & broken down in metabolism;
Metabolism: adequate protein & zinc required to release vitamin A from liver; hydrogenation destroys vitamin A& carotenes;
Interactions: oral contraceptives;

Functions of vitamin A

Necessary for health of all cells;
Involved in vision, smell, hearing, taste, growth, bone development, cell differentiation & reproduction;
Required for protein synthesis, RNA synthesis, cell division, cell membrane stability, production of light-sensitive visual pigments, mucus production, sexual & reproductive processes, sperm production, egg development, functions of adrenal & thyroid glands (metabolic rate, energy level, body temperature, growth rate), skin integrity, functions of inner lining of digestive tract, bone development & remodelling, liver function;
Protects against infections in nose, throat, lungs, digestive tract, urinary tract;
Involved in wound healing;
Beta carotene (anti-oxidant) traps free radicals, protecting against damage from pollution & cigarette smoke; quenches singlet oxygen; protects skin from UV sunlight damage;
Functions antagonized by: low thyroid may result in vitamin A depletion by slowing down conversion of beta-carotene; diabetes also interferes with conversion;

Quantities

Measurement: 1,000,000 micrograms (μg) = 1,000 milligrams (mg) = 1 gram (g);
1 μg of retinol (vitamin. A) = 1 retinol equivalent (RE), (new international standard);
1 RE = 1 μg = 3.3 IU = 6 μg beta-carotene = 12 μg other pro-vitamin A carotenoids;
Optimum: (SONA) average ranges from 800 to 2,000 μg /day for vitamin. A, and 5 to 10 mg/day of beta-carotene;
Individual optimum must be determined for each individual case; depends on nutritional status & body’s need;
Minimum: (DRI) set at 700/900μg (2300/2700 I.U.) /day, no RDA set for beta-carotene: suggested intake is 6 to 10 mg/day, or more;
Less than RDA: 50% of population, according to a U. S. government survey;
Deficiency of vitamin A results from lack in diet, poor absorption (inflammatory bowel disease, sprue, infection, parasites, diseases), mineral oil, excess or deficiency of protein, excess alcohol & iron, strenuous physical activity within 4 hours of a meal); inefficient conversion (thyroid deficiency, diabetes) or impaired storage (degenerative liver disease, cirrhosis, jaundice); cystic fibrosis; deficiency of fat (also protein) in diet; smoking; environmental pollution; increased need during pregnancy & lactation;
Symptoms include: dry skin; lacklustre hair; dandruff; “goosy”, bumpy hair follicles, esp. back of arms; poor nails; loss of sense of smell; softening of bones and teeth; drying & thickening of cornea (xerophthalmia); night blindness; blindness; stunted growth in children due to impaired hormone, membrane, & skeleton biochemistry; increased cell membrane permeability; skin & mucous membrane infections; respiratory disease; diarrhoea; parasitic & infectious diseases; reduced level of white blood cells; senility from oxidative damage to brain tissues; psoriasis; birth defects (cleft palate, congenital eye & heart defects); calcium phosphate kidney stones; precancerous changes in epithelial tissues of skin & lining of digestive tract (site of 50% of cancers); immune deficiency; cancer;
Toxicity from intake of vitamin A is unusual; requires more than 10 times RDA;
Beta-carotene produces orange-coloured skin, but is 100% non-toxic;
Vitamin A toxicity requires more than 50,000 IU/day over an extended time;
Toxicity symptoms: enlargement of liver & spleen; lethargy; headache, nausea, abdominal pain, diarrhoea; hair loss, dry skin; menstruation stops; bone re-ineralization;
In infants: scaly dermatitis, weight loss, anorexia, skeletal pain;
Toxicity reversed by stopping intake; recovery rapid & complete, often within 72 hours of stopping;

Therapy with vitamin A

Usual therapeutic dose is 5,000 to 25,000 IU/day;
Glaucoma, conjunctivitis, nearsightedness, crossed eyes, Betot spots (raised white patches of the white of the eyes);
10,000 IU of vitamin A plus 400 mg of vitamin B-2 may help reverse cataracts;
Tinnitus; migraine headaches;
100,000 IU of vitamin A over 4 to 6 months lower high cholesterol, but do not alter normal cholesterol levels;
Protection against carcinogenic agents; enhanced immunity;
Helps treat acne & its lesions, psoriasis, dandruff, bedsores, burns, warts, eczema;
Bronchial asthma, rhinitis, emphysema; nephritis; cirrhosis of the liver;
Beta carotene used to enhance immune response (macrophages); and prevention of cancers, esp. lung & cervix;