(Retinol, retinal, retinoic acid)
Vitamin A is a group of nutritionally unsaturated hydrocarbons, which include retinol, retinal, retinoic acid and several pro-vitamin A carotenoids. It is
involved in the formation and maintenance of healthy skin, hair and mucous membranes. Vitamin A helps humans to see in dim light and is necessary for proper bone growth, tooth development and reproduction. It assists the immune system and its antioxidant properties protect against pollution, cancer formation and various diseases. It also assists with the 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 the skin and is important in the storage of fat and the synthesis of protein and glycogen. Adequate levels of zinc is needed to transport vitamin A to the retina.
Two forms of vitamin A are available in the human diet: preformed vitamin A (retinol and its esterified form, retinyl ester) and provitamin A carotenoids. Preformed vitamin A is found in foods from animal sources, including dairy products, fish, and meat (especially liver). By far the most important provitamin A carotenoid is beta-carotene; other pro-vitamin A carotenoids are
alpha-carotene and beta-cryptoxanthin. The body converts these plant pigments into vitamin A. Both pro-vitamin A and preformed vitamin A must be metabolised intracellularly to retinal and retinoic acid, the active forms of vitamin A, to support the vitamin's important biological functions. Other carotenoids found in food, such as lycopene,
lutein and zeaxanthin, are not converted into vitamin A.
Vitamin A helps to move iron from storage in the body, without adequate amounts of vitamin A the body cannot regulate iron properly leading to an iron deficiency.
Deficiency of vitamin A
Deficiency can cause depression. It may also lead to eye problems with dryness of the conjunctiva and cornea, 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 become severe, the cornea can ulcerate and permanent blindness can follow. Abscesses forming in the ear, sinusitis, frequent colds 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 a sign that this vitamin is in short
supply. The hair and scalp can also become dry with a deficiency, especially if protein is also lacking. Prolonged deficiency leads to the rapid loss of vitamin C.
NOTE: High levels of vitamin A consumption can cause birth defects so the foods below are best limited during pregnancy and supplements containing vitamin A should be avoided
completely. Too much vitamin A interferes with vitamin D in the body
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