Unless your ill and need it right away, use a carotene source, not vitamin A. Because it is an oil-soluble vitamin, over a period of time, you can get too much vitamin A.
Functions: Vitamin A (and carotenes) keeps mucous membranes healthy; thus it protects against infections, even in infants.
It is extremely important in fighting infections.
It prevents night blindness, eye diseases, and weak eyesight.
It is important for skin, hair, gastro-intestinal juices and digestion.
It prevents premature aging and senility, and increases lifespan.
It helps blood capillaries work better and protects against cardiovascular diseases.
It affects growth and development, necessary for reproduction, and helps the immune system.
It protects against death among children with measles. Carotene provides far more antioxidant effect than vitamin A.
It is important in treating skin disorders, dry eyes, cancer, light sensitivity of eyes, and vaginal candidiasis.
Vitamin A (retinol) is a pure yellow, fat-soluble crystal. (Its other name, retinol, comes from the fact that it is found in the retina of the eye.) Vitamin A is found in meat, milk, and eggs.
The safer and very nutritious carotenes (also called carotenoids) are pro-vitamin A. They are found in abundance in fruits and vegetables, and are converted by the liver into vitamin A. It is always safe to take carotene in larger amounts, because the liver only converts the amount needed by the body into vitamin A.
Richest Sources: Dark green leafy vegetables.
Other Sources: Green and orange fruits and vegetables, especially carrots, lighter green vegetables, yams, tomatoes, mangos, Hubbard squash, cantaloupe and apricots. Lesser amounts are in legumes, grains, and seeds.
Beta-carotenes: These are the most active form of carotenes and are most abundant in green plants, carrots, sweet potatoes, squash, apricots, and green peppers. The best supplement form of carotenes is non-hydrogenated palm oil (absorbed 4-10 times better than any other type). In addition, palm oil has minimal fat content.
Carotenes are the most widespread group of naturally occurring pigments in nature, and are intensely colored (red and yellow) fat-soluble compounds. Along with chlorophyll, they are used by plants in photosynthesis to make carbohydrates (sugars, starches, and cellulose). Of the more than 600 carotenes, only 30-50 have vitamin A activity. Beta-carotene has the most pro-vitamin A activity, but several other carotenes have greater antioxidant effects. One of the richest sources of carotene is freshly made carrot juice.
Absorption Factors: Conversion of carotenes into vitamin A depends on protein status, thyroid hormones, zinc, and vitamin C, D, E, and choline. Both vitamin A and carotene absorption require essential fatty acids and zinc. When an adequate intake of carotenes is achieved after a meal, no further absorption occurs. Vitamins C, D, E, and choline in the diet, and bile action by the liver is needed for absorption of vitamin A and carotenes. The presence of some fatty acids in the meal (vegetable oil, etc.) increases vitamin A and carotene absorption. Liver disease reduces their utilization by the body.
Dosage and Cautions: RDA 5,000 IU/ODA 5,000 IU/TDA 20,000-300,000 IU. Best to take it only in the form of beta carotene; which is the vegetable-source precursor of vitamin A. The therapeutic dose of vitamin A (not carotene) would be 25,000 units for only a few days. It is dangerous to take too much vitamin A (which is oil soluble and stores well). In contrast, carotene is safe. The liver will only convert as much of vitamin A as is needed. During an acute viral infection, a single oral vitamin A dose of 50,000 IU for 1-2 days (at the most) is safe, even in infants. Over-dosage of vitamin A is dangerous.
Other Dosage Cautions: Do not normally take more than 5,000 IU a day. Do not take large amounts of it for a long period of time. Regular use of 50,000 IU can cause weakness, hair loss, headaches, enlarged liver and spleen, anemia, stiffness, and joint pain. Beware of fish liver oils. They are extremely rich in vitamin A and D, and can damage the heart muscle. Women who might be pregnant must not use vitamin A supplements; instead, use beta carotene. Accidental ingestion of a single large does of vitamin A (100,000-300,000 IU) reduced acute toxicity in children; but, if no more is taken, complete recovery will result. Toxicity occurs in adults who take more than 50,000 IU per day for several years. Women of childbearing age must be careful when taking vitamin A. Daily doses of 10,000 IU (found in some supplements) during the first three months of pregnancy are possibly linked to birth defects.
Deficiency symptoms: Prolonged deficiency can produce frequent colds, retarded growth, lack of appetite, and vigor, eye infections, poor vision, night blindness, frequent infections, bad teeth and gums, scaly and dry skin, weakened sense of smell and hearing.
Toxicity symptoms: Dry and fissured skin, brittle nails, alopecia, gingivitis, chapped lips, anorexia, irritability, fatigue, nausea, intracranial pressure with vomiting, headache, joint pain, stupor, papilledema. Prolonged toxicity results in bone fragility, and thickening of long bones. There are never any toxicity symptoms from taking carotenes.