Vitamin A

Sources: Vitamin A, a fat-soluble vitamin, occurs in two principal forms in nature: retinol and certain carotenoids. Retinol is found only in animal sources, in foods such as fish, meat, eggs and full fat milk. In plant foods, vitamin A can be obtained from a family of substances called carotenoids which are found in brightly coloured fruit and vegetables, and green leafy vegetables. The best known form of carotenoid is beta-carotene (pro-vitamin A). beta-Carotene can be converted to retinol in the body when it is needed.
Vitamin A is stored in the liver. The stores of vitamin A in the liver of a well nourished adult can supply the body's needs for several months. Regularly taking large amounts of vitamin A can exceed the liver's storage capacity, resulting in adverse effects on the body. However it is unlikely that anyone on a normal diet could get too much of this vitamin. When vitamin A is obtained from beta-carotene, there is no danger of excess intake because it is formed in the body only when it is needed.

Below: A microscopic image of vitamin A

Functions: Vitamin A is essential for vision, adequate growth and tissue differentiation.

Deficiency: Deficiency symptoms include night blindness, hyperkeratinosis of the skin, and xerophthalmia, an eye condition which if untreated can lead to permanent blindness. Vitamin A deficiency is still widespread in many developing countries. A shortage of vitamin A also affects antibody production and resistance to disease. The diet of farm animals needs to be fortified with vitamin A for optimum health, performance and fertility. This is because the beta-carotene content of green fodder plants drops rapidly after harvest.

Production: Although it has been known since the time of ancient Egypt that certain foods would cure night blindness, vitamin A per se was not identified until 1913. Its chemical structure was defined by Paul Karrer in 1931. Professor Karrer received a Nobel Prize for his work, because this was the first time that a vitamin structure was determined.

Product forms: DSM vitamin A is available as retinyl acetate or retinyl palmitate in oily or dry forms, and in combination with vitamin D3.