Vitamin A actually an assembly of unsaturated and double bonded organic compounds in which carbon is major element of its structure, it is known as retinol, retinal and retinoic acid (because of their structure and position of its atoms).
Vitamin A is a group of fat-soluble compounds that can be differentiated into two categories, depending on whether the food source is an animal or a plant:
• Vitamin A found in foods that come from animals is called preformed vitamin A or retinol
• Vitamin A found in fruits and vegetables is called provitamin A carotenoid
Animal source derived vitamin A is known as Preformed Vitamin A (retinol) is chiefly found as retinly palmitate in the major of supplements of Vitamins, fortified foods and in the livers of animals.
Proformed is actually the inactive form of vitamin A that are present in plants, approximately fifty Provitanin A is carotenoids that are actually α-carotene, β-carotene and β-cryptoxanthin. β-carotene is less easily absorbed than retinol and must be converted to retinal and retinol by the body.
Two micrograms (mcg) of β-carotene in oil provided as a supplement can be converted by the body to 1 mcg of retinol giving it an RAE (retinol activity equivalent) ratio of 2:1. However, 12 mcg of β-carotene from foods are required to provide the body with 1 mcg of retinol, giving dietary β-carotene an RAE ratio of 12:1.
Food rich in retinol include meat, butter, retinol-enriched margarine, dairy products and eggs, while foods rich in β-carotene include vegetables and fruits (e.g. sweet potatoes, carrots, dark-green leafy vegetables, sweet red peppers, mangoes, melons).
The main physiological active forms of vitamin A are retinaldehyde and retinoic acid, both of which are derive from retinol.
The vital biological roles of vitamin A compounds include normal cell growth, cell differentiation, vision and immunology.
Properties of vitamin A
