There are two sources of human vitamin A, one is found in animal food (); The other is found in plants, as follows:

There are two sources of human vitamin A, one is retinol in animal food, and the other is β -carotene in plant food.

1. Brief introduction of vitamin A

Vitamin A is a fat-soluble vitamin, and its chemical formula is C2H3O. It is stable to heat, acid and alkali and easy to be oxidized. Ultraviolet rays can promote its oxidative damage. Vitamin A includes A1 and A2, A1 is retinol. Vitamin A2 is 3- dehydroretinol, and its physiological activity is 4% of that of vitamin A1.

2. the structure of vitamin a

vitamin a refers to all compounds with the biological activity of retinol. There are two kinds of substances that can provide the biological activity of retinol. One refers to retinol, its metabolites and synthetic analogues with similar structures, which are also called Retinoids, also known as preformed vitamin A. The main dietary sources are retinol and retinyl esters contained in animal foods.

Another kind of substance is vitamin A protocarotenoid, which refers to carotenoids from plant foods that can be converted into retinol in vivo. They are precursors of dietary retinol, mainly including β-carotene, α-carotene and β-cryptoxanthin.

3. Function and deficiency of vitamin A

Vitamin A has many physiological functions, such as promoting growth and reproduction, maintaining normal secretion of bones, epithelial tissues, vision and mucosal epithelium, and vitamin A and its analogues can prevent precancerous lesions.

when it is deficient, it is characterized by slow growth and decreased dark adaptability, resulting in night blindness. Due to the dryness, desquamation, hyperkeratosis and decreased lacrimal gland secretion of epidermal and mucosal epithelial cells, dry eye occurs, and in severe cases, corneal softening and perforation lead to blindness. Epithelial cells of respiratory tract keratinize and lose cilia, which reduces their resistance and makes them susceptible to infection.

4. Food sources of vitamin A

Food sources of vitamin A include livers, egg yolks and milk powder of poultry and livestock. Carotene can be converted into vitamin A in small intestinal mucosa, red, yellow and dark green vegetables, and fruits contain more carotene. Animal liver (very little added) pumpkin, carrot, spinach, celery, Chinese cabbage, etc.