EYES - Vitamin A is essential for eyes to function effectively. It is involved in the growth and repair of the eye and in the production of a chemical called visual purple, which helps in night vision.EPITHELIAL CELLS - Vitamin A is involved in the growth and repair of epithelial cells. These cells cover the internal and external surfaces of the body and are found in the skin, lungs, developing teeth, inner ear, cornea of the eye, sex organs, glands and their ducts, gums, nose, cervix and other areas. This growth and maintenance role is vital for many bodily functions. For example, the good health of the digestive tract lining is important in protecting against ulcers and maintenance of the lining of the vagina and uterus which are important in fertility.PREGNANCY - Vitamin A is necessary in pregnancy for the development of the embryo.NERVES - Vitamin A is involved in the production of membranes and of myelin, which coats the nerves.GLANDS AND HORMONES - Vitamin A plays a role in the maintenance of the adrenal gland and synthesis of certain hormones such as thyroid hormone.THE IMMUNE SYSTEM - Vitamin A is known as "the anti-infective vitamin" as it is vital for the development of the body’s natural defenses. It stimulates and enhances many immune functions. This immune enhancing function promotes healing of tissues and increases resistance to infection.Adequate vitamin A intake, either from diet or supplements, is very important especially for children. Many studies have found that vitamin A supplementation reduces the risk of infectious diseases in areas where vitamin A deficiency is widespread.
A recent research review of several studies found that adequate vitamin A intake in children resulted in many health benefits. Children in developing countries are often at high risk of vitamin A deficiency. In developed countries, ensuring adequate vitamin A intake is particularly important for immune support.GROWTH AND BONE FORMATION - Vitamin A is necessary for growth and the formation of bones and teeth, collagen synthesis, cartilage synthesis and wound healing.ANTIVIRAL ACTIVITY - Laboratory experiments have shown vitamin A to have antiviral activity.
EYES - One of the first symptoms of deficiency is night blindness due to lack of visual purple. Prolonged deficiency leads to xerophthalmia, a condition in which eyes become dry, ulcers appear on the cornea, the eyelids become swollen and sticky and which eventually leads to blindness. Vitamin A deficiency is the leading preventable cause of blindness in developing countries.SKIN - Prolonged deficiency leads to thickened dry skin which is prone to infections. Small hardened bumps of a protein known as keratin may develop around the hair follicles.GROWTH - Deficiency causes growth retardation, weight loss, diarrhea, thickening of bone shafts, congenital malformations, impaired hearing, taste and smell, wasting of testicles and reduced sperm count. Inadequate vitamin A intake may lead to improper tooth formation in children and to gum disease.IMMUNE SYSTEM - Epithelial surfaces are adversely affected by vitamin A deficiency causing increased susceptibility to skin and respiratory infections. Immune cells and antibody functions are also affected which may lead to an increase in pre-cancerous cells in the epithelial tissues of the mouth, throat and lungs.THYROID GLAND - A deficiency of vitamin A can contribute to lower levels of active thyroid hormone with symptoms of low body temperature, depression, difficulty in losing weight, headaches and lethargy.
Vitamin A supplements are used in developing countries to prevent or treat deficiency and to protect immune system function.
SKIN DISORDERS - The vitamin A derivatives etretinate and isotretinoin are used topically to treat psoriasis. These compounds inhibit the formation of some of the toxic compounds which may be responsible for the high rate of cell division causing the scaly build up on the skin.
Vitamin eye drops have been used to treat dry eyes.Creams containing vitamin A have been used to heal wounds in patients taking corticosteroid drugs.
Vitamin E and zinc are necessary for vitamin A metabolism, including absorption, transport and release from the liver. Vitamin E may protect against some of the effects of excess vitamin A.Vitamin A is necessary for calcium metabolism in the formation of healthy bones and teeth.Vitamin A absorption is reduced by mineral oil laxatives, which bind it. Antacids, the anti-gout drug colchicine, and the cholesterol reducing drug, cholestyramine inhibit vitamin A absorption.Alcohol irritates the digestive tract and inhibits the absorption of vitamin A while also depleting the body’s tissue stores.
Pre-formed vitamin A supplements in doses of more than 3000 mg RE should not be taken by women who may become pregnant. Pro-vitamin A, or beta-carotene are safe for pregnant women.
Vitamin A supplements should not be taken with isotretinoin or etretinate for skin disease or in cases of impaired liver or kidney function. If vitamin A supplements are taken with large amounts of alcohol, liver damage may occur.Broad spectrum antibiotics should not be taken with high doses of vitamin A.
- in leafy green vegetables
- in yellow fruits and vegetables
- in the liver oils of the cod and other fish
- in milk, cheese, butter and egg yolk