Picture of Vitamin A

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Vitamin A structure
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Picture of Vitamin A

Vitamins are substances that play an essential part in animal metabolic processes, but which the animals cannot synthesise. In their absence the animal develops certain deficiency diseases or other abnormal conditions. Vitamins are chemicals other than proteins, carbohydrates, fats and mineral salts that are essential constituents of the food of animals. Although certain animals can synthesise certain vitamins and all animals needing vitamin D can manufacture it from ergosterol in the presence of u.v. light, the precise mechanism of action of many vitamins is still poorly understood. Small amounts of vitamins are essential for the regulation of all bodily processes. With the exception of vitamin D, the human body cannot make its own vitamins, and some cannot be stored. Vitamins must therefore be obtained from a food on a daily basis. A person's diet must provide all the necessary vitamins.

Vitamin A is required for healthy skin and mucus membranes, and for night vision. Its absence from diet leads to a loss in weight and failure of growth in young animals, to the eye diseases; xerophthalmia, and night blindness, and to a general susceptibility to infections. It is thought to help prevent the development of cancer.

Vitamin A is structurally related to carotene. Carotene is converted into vitamin A in the liver, two molecules of vitamin A are formed from on molecule of beta carotene, hence good sources of carotene, such as green vegetables are good potential sources of vitamin A. Vitamin A is manufactured by extraction from fish-liver oil and by synthesis from beta-ionone.

Good sources of Vitamin A - Butter, margarine, milk, cheese yogurt, cream, sweet potatoes, butternut squash, carrots, red peppers, chilies, leeks lettuce, broccoli, Swiss chard, spinach, tomatoes, watercress, basil, coriander, parsley, apricots, cantaloupe melons, mangoes, papayas, guavas, Sharon fruit.

Update by Karl Harrison
(Molecule of the Month for February 1997 )