Vitamin A
3500 years ago, the Chinese used a concoction rich in Vitamin A to cure nightblindness, a common Vitamin A deficiency. The ancient Greeks did the same. Hippocrates prescribed various forms of liver for the condition. Modern science, however, did not distinguish it as a viable nutrient until the early 1900's. The synthetic form of Vitamin A became available in 1947. Vitamin A consists of several active compounds, including retinal, retinene, retinaldehyde, retinol (found in animal foods), retinoic acid, and carotenoids (found in plants).
Retinoids are a group of compounds consisting of retinol, retinaldehyde, and retinoic acid, along with a large number of synthetic analogs with or without Vitamin A activity. Retinoic acid is formed through the oxidation of Vitamin A aldehyde. It has no activity in the visual process or the reproductive system and cannot be stored in the body. Retinol has two well known forms, consisting of Vitamin A1 (retinol found in saltwater fish) and Vitamin A2 (dehydroretinol found in freshwater fish). Vitamin A2 differs from A1 in that it has more conjugated double bonds and has about 1/3 the biologic activity.
With over 600 known carotenoids, fewer than fifteen have any significance to human health. Carotene is actually two "vitamin A" molecules hooked tail-to-tail. In this form, Vitamin A is inactive and, therefore, non-toxic, no matter the dosage. As the body needs Vitamin A, and only then, does it split the carotene molecules to make an active form. Conversion to the active vitamin takes place within the intestinal wall and in the liver, with only about 10% of carotenoids being converted into Vitamin A at any given time. Carotenes are available in such foods as carrots (alpha), algae (beta), tomatoes (lycopene), and spinach and broccoli (lutein and zeaxanthin).
The most commonly used and recognized carotenoid is beta-carotene, which is also the easiest to convert to Vitamin A internally. The body is able to regulate this conversion, thereby preventing the development of toxic levels of carotene. However, it does not act in the same manner to retinol. This is the reason why toxicity has occurred in some people taking mega doses of the retinol form of Vitamin A. There have not been any reports of toxicity from beta-carotene, despite sustained doses of 500,000 IU daily! Retinol, on the other hand, can produce toxic symptoms in levels exceeding 15,000 IU per day. Warnings of Vitamin A toxicity rarely make this distinction.
As an antioxidant, beta carotene is proving to increase immunity. In addition, numerous studies have indicated its protective qualities against various forms of cancer, including bladder, larynx, esophogus, stomach, colon/rectal, and prostate. Very high doses have substantially reduced the destructive consequences of immunosuppressive therapies (chemo and radiation) in cancer patients. Experts still are unsure whether it is the influence of carotenoids on cancer alone or whether it is other substances found in fruits and vegetables high in carotenoids that are responsible. Therefore, food, in conjunction with supplements, includes the best of both worlds. One should not be preferred over the other.
Carotene can build up in the body though, causing the skin to turn yellowish or orangey, but this is not cause for alarm. Jaundiced skin may indicate an excessive intake of beta carotene or a liver disease. The only way to distinguish this abnormality from jaundice is to look at the whites of the eyes. Jaundice will turn the whites yellowish, but excessive carotene will not.
A deficiency in just one nutrient can lead to various eye disorders (see separately). Since Vitamin A is an antioxidant, it helps protect against Free Radicals which attack structural proteins, enzymes, and cell membranes of the lens. Vitamin A is essential for maintaining the mucus membranes lining the eye. These membranes provide resistance to bacterial invasions and tissues and, weakened by a lack of Vitamin A, are more susceptible to infections.
Vitamin A is required for the regeneration of rhodopsin. Rhodopsin (formerly called "visual purple") is the pigment in the rods of the retina that contains this vitamin. On exposure to light, it is bleached through a series of products, eventually forming opsin and another pigment known as retinaldehyde ("visual yellow"). As a result of these changes, images are transmitted to the brain through the optic nerve.
A Vitamin A deficiency can sometimes produce a condition known as corneal xerosis, which is a hazy, milky, or opaque appearance of the cornea, usually in the lower central area. However, this condition can also be caused by other factors, as well as a vitamin deficiency.
Measles dramatically increases the need for Vitamin A. The virus, a member of the RNA group called paramyxovirus, quickly diminishes stores. Supplementation is advised. Children, having low levels of Vitamin A to begin with, are at a greater risk of succumbing to the disease. Vitamin A given to children in the third world has cut the death rate from measles by a minimum of 35%.
Palmitate and acetate are synthetic forms of Vitamin A found in supplements and foods. Tretinoin and isotretinoin are special forms used to treat acne and can only be obtained by prescription and do not meet the body's requirements for Vitamin A. Other retinoids have been developed for such specific uses as in cancer research, and cannot be purchased. They are described as "Vitamin A analogs."
A Vitamin A deficiency can cause a condition known as follicular keratosis, hyperkeratosis, or xeroderma, in which there is excessive production of keratin, a hard protein. Keratin deposits form around the hair follicles, resulting in a rough texture to the skin resembling 'goose flesh.' Facial skin that is scaly, off-color, cracked, or dry to the point of flaking may be attributed to a combination of PEM (protein energy malnutrition) and a lack of Vitamin A and iron.
Summary:
There are various forms of Vitamin A each having distinct characteristics. These include: Provitamin A, Vitamin A1, Vitamin A2, Vitamin A acetate, Vitamin A acid, Vitamin A aldehyde, Vitamin A epoxide, Vitamin A palmitate, and Neovitamin A.
Provitamin A is converted internally to Vitamin A.
Names include: Vitamin Ao, carotene, beta-carotene.
Forms include: alpha carotene (which is only half as potent as beta carotene known to be the most potent); gamma carotene (low potency); delta carotene or epsilon; and psi-carotene.
Inhibitors include: ferrous sulfate, polyunsaturated fats, laxatives, mineral oil.
Helpers include: B Complex, Vitamins Bp, C, D, E, calcium, phosphorus, and zinc.
Deficiencies produce: a lost source of Vitamin A and its benefits since it is the precursor.
Note: Diabetics are not able to convert carotene to Vitamin A. Therefore, adding increased amounts will only cause adverse side effects.
Vitamin A is also known as: antixerophthalmic vitamin/factor; anti-infective vitamin/factor; lard factor; axerophthol; biosterol; and oleovitamin A.
Forms include: Vitamin A1 or retinol; Vitamin A acetate; Vitamin A acid; Vitamin A aldehyde; Vitamin A epoxide; Vitamin A palmitate; Vitamin A2 or dehydroretinol; Neovitamin A; and provitamin A.
Inhibitors include: mineral oil, strenuous physical activities during digestion, ferrous sulfate, dicumarol, laxatives, steroids, PCB's (polychlorinated biphenol), sodium benzoate, nitrites, aflatoxins, DDT, dielrin, diarrhea, bilary and pancreatic dysfunction, cardiac disease, and a Vitamin D deficiency.
Helpers are: B complex vitamins, Vitamin Bp, Vitamins C, D, E, calcium, phosphorus, and zinc.
Deficiency symptoms include: night blindness, itchy eyes, deterioration of tear ducts, bloodshot eyes, sties, corneal thickening and softening, acne, skin rashes, rough or dry skin, eczema, enlarged follicles, dry or brittle hair, decreased appetitie, deterioration of GI tract and salivary glands, decreased sense of smell, fatigue, reduced weight, retarded growth, decreased immunity, infections, sterility, too little decreases Vitamin C levels, decreases cancer resistance, slows healing, increases menstrual bleeding and birth defects, deterioration of lactation.
Toxicity symptoms include: dry skin, itching, profuse sweating, peeling/scaling/thickening skin, sore lips, sparse/coarse/brittle hair, brittle nails, decreased eyebrow hair, increased cranial pressure, blurred vision, protruding eyes, irregular menses, headaches, emotional agitation, nausea, abdominal pain, decreased appetite, diarrhea, muscle weakness, fatigue, bone thickening, demineralization of bones, aching bones or joints, enlarged spleen/liver/kidneys, retarded growth, decreased immunity, and the development of some cancers. Detoxified with Vitamin C.
Vitamin A1 is also known as retinol, Acon, Afaxin, Agiolan, Alphalin, Anatola, Aoral, Apexol, Apostavit, Atav, Avibon, Avita, Avitol, Axerol, Dohyfral A, Epiteliol, Nio-A-Let, Prepalin, Testavol, Vaflol, Vi-Alpha, Vitpex, Vogan, Vogan-Neu.
Vitamin A2 is the same as dehydroretinol.
Vitamin A acetate is a specific form of Vitamin A.
Vitamin A acid is a specific form of Vitamin A also known as retinoic acid, tretinoin, Aberel, Airol, Aknoten, CordesVas, Dermairol, Epi-Aberel, Eudyna, Retin-A.
Vitamin A aldehyde is a specific form of Vitamin A.
Vitamin A epoxide is a specific form of Vitamin A also known as hepaxanthin or monoepoxyvitamin A.
Vitamin A palmitate is a specific form of Vitamin A.
Neovitamin A is a specific form of Vitamin A also called 5-cis-vitamin A.
