Discovery of vitamin A:
The discovery of vitamin A may have stemmed from research dating back to 1906, indicating that factors other than carbohydrates, proteins and fats were necessary to keep cattle healthy. By 1917 one of these substances was independently discovered by Elmer Me collum at the University of wisconcin-Madision and Lafayette Mendel and Thomas Burr Osborne at Yale University. Since water soluble factor B(vitamin-B) had recently been discovered, the researchers chose the name "fat-soluble factor A" (vitamin A). In 1919, Steenbock (University of Wisconsin) proposed a relationship between yellow plant pigments (beta-carotene) and vitamin A. Vitamin A was first synthesized in 1947 by two Dutch chemists, David Adriaan van Dorp and Jozef Ferdinand Arens.
Vitamin A (or Vitamin A Retinol, retinal, and four carotenoids including beta carotene) is a vitamin that is needed by the retina of the eye in the form of s specific metabolite, the light absorbing molecule retinal, that is necessary for both low high (scotopic vision) and color vision. Vitamin A also functions in a very different role as an irreversibly oxidized form of retinol known as retinoic acid, which is an important hormone-like growth factor for epithelial and other cells.
In foods of animal origin, the major form of vitamin A is an ester, primarily retinyl palmitate, which is converted to the retinol (chemically an alcohol) in the small intestine. The retinol form functions as a storage form of the vitamin, and can be converted to and from its visually active aldehyde form, retinal. The associated acid (retinoic acid), a metabolite that can be irreversibly synthesized from vitamin A, has only partial vitamin A activity, and does not function in the retina for the visual cycle.
All forms of vitamin A have a beta-ionone ring to which an isoprenoid chain is attached, called a retinyl group. Both structural features are essential for vitamin activity the orange pigment of carrots-beta carotene– can be represented as two connected retinyl groups, which are used in the body to contribute to vitamin A levels. Alfa carotene and gamma- carotene also have a single retinyl group, which give them some vitamin activity. None of the other carotenes have vitamin activity. The carotenoid beta-cryptoxanthin possesses an ionone group and has vitamin activity in humans.
Source:
Vitamin A and carotene can be obtained from either animal or vegetable sources. The animal form is divided between retinol and dehydroretinol whereas the vegetable carotene can be split into four very potent groups - alpha-carotene, beta-carotene, gamma-carotene and crypto-carotene. With enough beta-carotene available in the body, the body can manufacture its own vitamin A.
Food sources of vitamin A:
Liver, milk, egg-yolk, carrots, dark green leafy vegetables and yellow fruits are high in vitamin A or beta-carotene.
Requirement:
Vitamin A is required for night vision, and for a healthy skin. It assists the immune system, and because of its antioxidant properties is great to protect against pollution and cancer formation and other diseases. It also assists your sense of taste as well as helping the digestive and urinary tract and many believe that it helps slow aging.
It is required for development and maintenance of the epithelial cells, in the mucus membranes, and your skin, and is important in the formation of bone and teeth, storage of fat and the synthesis of protein and glycogen.
A deficiency of vitamin A may lead to eye problems with dryness of the conjunctiva and cornea, dry skin and hair, night blindness as well as poor growth.
Dry itchy eyes that tire easily are normally a warning of too little vitamin A. If the deficiency becomes severe, the cornea can ulcerate and permanent blindness can follow.
Abscesses forming in the ear, sinusitis, frequent cold and respiratory infections as well as skin disorders, such as acne, boils and a bumpy skin, as well as weight loss might be indicative of the vitamin being in short supply.
Insomnia, fatigue and reproductive difficulties may also be indicative of the vitamin in short supply. Your hair and scalp can also become dry with a deficiency, especially if protein is also lacking.
When more required:
More of this vitamin is required when you consume alcohol, on a low-fat diet, or a diet high in polyunsaturated fatty acids, if you smoke or live in a polluted area. It may also be indicated if you suffer from diabetes or have an under-active thyroid gland. Be careful of vitamin A in pregnancy.
Enemy of vitamin A:
Retinol is destroyed by light, high temperatures as well as when using copper or iron cooking utensils. Beta-carotene rich vegetables and fruit must not be soaked in water for long periods, since the nutrients can be lost like that.
Daily doges:
The dosage underneath is the Recommended dietary allowances (RDA), but be aware that this dosage is the minimum that you require per day, to ward off serious deficiency of this particular nutrient. In the therapeutic use of this nutrient, the dosage is usually increased considerably, but the toxicity level must be kept in mind.
Male 5,000 IU per day (1,000 µg equivalent).
Female 4,000 IU per day (800 µg retinol equivalent).
Toxicity and symptoms of high intake:
Dosages exceeding 15,000 IU per day must be taken under medical supervision. Toxicity can appear in some individuals at relatively low dosages and the symptoms may include nausea, dizziness, menstrual problems, skin changes and dryness, itchiness, irritability, vomiting, headaches and long term use can cause hair loss, bone and muscle pain, headache, liver damage, and an increase in blood lipid concentrations. Pregnant women must be careful as a high intake of this vitamin can cause birth defects. Pro-vitamin A - beta-carotene does not cause toxicity.
Be careful if you in the unlikely event run across polar bear on a menu - 500 gram (about ½ a pound) of polar bear liver will deliver about 9,000,000 IU to your diet - a very lethal dose. Headaches, blurred vision, loss of hair, drowsiness and diarrhea, enlargement of the spleen and liver can all be indications when your intake is too high.
The discovery of vitamin A may have stemmed from research dating back to 1906, indicating that factors other than carbohydrates, proteins and fats were necessary to keep cattle healthy. By 1917 one of these substances was independently discovered by Elmer Me collum at the University of wisconcin-Madision and Lafayette Mendel and Thomas Burr Osborne at Yale University. Since water soluble factor B(vitamin-B) had recently been discovered, the researchers chose the name "fat-soluble factor A" (vitamin A). In 1919, Steenbock (University of Wisconsin) proposed a relationship between yellow plant pigments (beta-carotene) and vitamin A. Vitamin A was first synthesized in 1947 by two Dutch chemists, David Adriaan van Dorp and Jozef Ferdinand Arens.
Vitamin A (or Vitamin A Retinol, retinal, and four carotenoids including beta carotene) is a vitamin that is needed by the retina of the eye in the form of s specific metabolite, the light absorbing molecule retinal, that is necessary for both low high (scotopic vision) and color vision. Vitamin A also functions in a very different role as an irreversibly oxidized form of retinol known as retinoic acid, which is an important hormone-like growth factor for epithelial and other cells.
In foods of animal origin, the major form of vitamin A is an ester, primarily retinyl palmitate, which is converted to the retinol (chemically an alcohol) in the small intestine. The retinol form functions as a storage form of the vitamin, and can be converted to and from its visually active aldehyde form, retinal. The associated acid (retinoic acid), a metabolite that can be irreversibly synthesized from vitamin A, has only partial vitamin A activity, and does not function in the retina for the visual cycle.
All forms of vitamin A have a beta-ionone ring to which an isoprenoid chain is attached, called a retinyl group. Both structural features are essential for vitamin activity the orange pigment of carrots-beta carotene– can be represented as two connected retinyl groups, which are used in the body to contribute to vitamin A levels. Alfa carotene and gamma- carotene also have a single retinyl group, which give them some vitamin activity. None of the other carotenes have vitamin activity. The carotenoid beta-cryptoxanthin possesses an ionone group and has vitamin activity in humans.
Source:Vitamin A and carotene can be obtained from either animal or vegetable sources. The animal form is divided between retinol and dehydroretinol whereas the vegetable carotene can be split into four very potent groups - alpha-carotene, beta-carotene, gamma-carotene and crypto-carotene. With enough beta-carotene available in the body, the body can manufacture its own vitamin A.
Food sources of vitamin A:
Liver, milk, egg-yolk, carrots, dark green leafy vegetables and yellow fruits are high in vitamin A or beta-carotene.
Requirement:
Vitamin A is required for night vision, and for a healthy skin. It assists the immune system, and because of its antioxidant properties is great to protect against pollution and cancer formation and other diseases. It also assists your sense of taste as well as helping the digestive and urinary tract and many believe that it helps slow aging.
It is required for development and maintenance of the epithelial cells, in the mucus membranes, and your skin, and is important in the formation of bone and teeth, storage of fat and the synthesis of protein and glycogen.
A deficiency of vitamin A may lead to eye problems with dryness of the conjunctiva and cornea, dry skin and hair, night blindness as well as poor growth.
Dry itchy eyes that tire easily are normally a warning of too little vitamin A. If the deficiency becomes severe, the cornea can ulcerate and permanent blindness can follow.Abscesses forming in the ear, sinusitis, frequent cold and respiratory infections as well as skin disorders, such as acne, boils and a bumpy skin, as well as weight loss might be indicative of the vitamin being in short supply.
Insomnia, fatigue and reproductive difficulties may also be indicative of the vitamin in short supply. Your hair and scalp can also become dry with a deficiency, especially if protein is also lacking.
When more required:
More of this vitamin is required when you consume alcohol, on a low-fat diet, or a diet high in polyunsaturated fatty acids, if you smoke or live in a polluted area. It may also be indicated if you suffer from diabetes or have an under-active thyroid gland. Be careful of vitamin A in pregnancy.
Enemy of vitamin A:
Retinol is destroyed by light, high temperatures as well as when using copper or iron cooking utensils. Beta-carotene rich vegetables and fruit must not be soaked in water for long periods, since the nutrients can be lost like that.
Daily doges:
The dosage underneath is the Recommended dietary allowances (RDA), but be aware that this dosage is the minimum that you require per day, to ward off serious deficiency of this particular nutrient. In the therapeutic use of this nutrient, the dosage is usually increased considerably, but the toxicity level must be kept in mind.
Male 5,000 IU per day (1,000 µg equivalent).
Female 4,000 IU per day (800 µg retinol equivalent).
Toxicity and symptoms of high intake:
Dosages exceeding 15,000 IU per day must be taken under medical supervision. Toxicity can appear in some individuals at relatively low dosages and the symptoms may include nausea, dizziness, menstrual problems, skin changes and dryness, itchiness, irritability, vomiting, headaches and long term use can cause hair loss, bone and muscle pain, headache, liver damage, and an increase in blood lipid concentrations. Pregnant women must be careful as a high intake of this vitamin can cause birth defects. Pro-vitamin A - beta-carotene does not cause toxicity.
Be careful if you in the unlikely event run across polar bear on a menu - 500 gram (about ½ a pound) of polar bear liver will deliver about 9,000,000 IU to your diet - a very lethal dose. Headaches, blurred vision, loss of hair, drowsiness and diarrhea, enlargement of the spleen and liver can all be indications when your intake is too high.
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