Vitamin A

What does it do? Is it Important?

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Vitamin A is a fat soluble vitamin, which means it is stored in the body and not excreted in the urine. It is present in food in two main forms, as preformed vitamin A which is the actual vitamin A, and as a precursor of vitamin A in the form of carotenes and carotenoids. Pro-vitaminA, or carotene, exists in abundance in yellow and orange pigments of many fruits and vegetables and is converted into vitaminA in the intestines.Most of the vitamin A in a mixed diet is supplied in the form of carotenoids.

Food sources of Vitamin A: Livers of animals are a rich source of vitamin A, fish liver oils, green and yellow fruits and vegetables, milk, cheese, butter, eggs,and many herbs including alfalfa, parsley, lemongrass, and watercress to name only a few.

Functions of Vitamin A : The most important function of vitamin A is the preservation of eye health, it is important to prevent drying of the eye, to maintain health of the cornea, and normal function of the retina. Vitamin A acts as an antioxidant, helping to protect the cells against disease, and to maintain new cell growth. It enhances immunity, plays an important part in the maintenance and repair of epithelial tissue, slows the aging process, is important in the formation of teeth and bones, aids in fat storage, and protects against infections.

"Retinal is found in the cells of the eye where it plays a vital part in the perception of light and this is the reason why the ‘old wives’ tale’ that carrots help you to see in the dark is, in fact, true. The speed at which the human eye adapts to seeing in the dark depends on the amount of vitamin A available in the body, known as the vitamin A status. A ‘dark adaptation test’ can be used as a measure of vitamin A status. Vitamin A deficiency is a major public health problem in the developing world, causing blindness in a quarter of a million people each year. Vitamin A supplements are successful in preventing blindness from this cause."

"Vitamin A also assists in keeping the epithelial cells of the body moist and healthy. As well as lining the whole of the digestive tract, epithelial cells cover the surfaces of the glands around the eyes and line the lungs (and are found elsewhere too). Xerophthalmia or dry-eye is a classic sign of vitamin A deficiency. Tear production is reduced and the eyes become susceptible to infections such as conjunctivitis. Children who are vitamin A-deficient are more susceptible to respiratory infections and measles. Vitamin A is involved in normal growth and bone formation and it plays a part in the production of red blood cells and therefore the prevention of anaemia."

Vitamin A deficiency signs: One of the first signs that the body may not be getting its quota of vitamin A is the loss of night vision. Another prominent sign of a vitamin A deficiency is a hyperkeratinization or drying out of the skin and mucous membranes, the skin appears crusty and rough.This drying out effect can prove very detrimental to health when the mucous membranes are affected, early signs of hyperkeratinization of the mucous membranes are loss of the sense of taste and smell. Mucous membranes affected by a vitamin A deficiency include the nose, sinuses, lungs, eyelids, mouth, throat, stomach, intestines, vagina, uterus, without the protective effects of vitamin A there will be incresed susceptibility to infection. There will be an inability to combat the invasive effects of micro organisms, and the harmful particles resulting from air pollution.

Loss of Vitamin A : Cooking vegetables causes a significant loss of vitamin A

Therapeutic uses of Vitamin A : Infectios diseases, middle ear infections, atheroma, asthma, rhinitis, poantar warts, night blindness, pancreatic and gall bladder disease, cancer, poor immunity, hyperthyroidism, dermatitis,multiple sclerosis, viral meningitis, hodgkin's disease, wound healing, inflammation of the kidney, and tinnitus.

Drugs affecting Vitamin A loss: Antibiotics, cortisone, oral contraceptives, cholesterol lowering drugs, and laxatives may all interfere with vitamin A absorption.

Dosage and Toxicity of Vitamin A: All fat soluble vitamins are capable of reaching toxic levels in the body, because they are stored in the body and are not excreted in the urine like the water soluble vitamins. The RDA 5,000-10,000 IU, exactly what is the ideal dose varies with the health and need of the individual. High doses of Vitamin A taken over a long period, can prove toxic. Signs of toxicity include, irritability, abdominal pain, enlargement of the liver or spleen, headache, fatigue, insomnia, painful bones and joints, abnormal bone growth, nausea and vomiting, jaundice, anorexia, hair loss and pruritis. Children and pregnant women are far better off to obtain their vitamin A from natural sources, such as organically grown fruits and vegetables.

"Vitamin A is toxic if taken in very large quantities and poisoning has occurred in Arctic explorers who have eaten polar bear liver, which is particularly rich in vitamin A. The concentration of vitamin A in lamb and calf liver has increased substantially in the last 20 years due to supplements to their feed. Pregnant women are advised to restrict their intake of liver and pâté made from liver, since there is some evidence that high doses of vitamin A can cause birth defects. However, vitamin A is an essential part of the human diet and severe health problems occur if there is a deficiency. Since dairy products, such as butter, are a good source of vitamin A, all types of margarine and similar spreads are now required by law to have vitamin A added to them, as you will see on their labels. Vitamin A, which is actually a group of interrelated substances (retinol, retinal and retinoic acid), can be synthesised in the body from β-carotene, found in dark-green leafy vegetables such as cabbage, sprouts, broccoli and spinach, and in carrots. Cooking the vegetables does not damage the β-carotene molecules and in fact β-carotene is more easily absorbed into the body from cooked carrots."

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