Vitamin A (retinol) affects the barrier function of the mucous membranes, skin, the permeability of cell membranes, the biosynthesis of their components. There are three vitamins A - A 1 , A 2 , cis-form of vitamin A 1 , called neovitamin A. Forms of vitamins of group A exist as stereoisomers, but only some have biological activity. The symptom of vitamin A deficiency in animals and humans is manifested in inhibition of growth, reduction in body weight, general exhaustion of the body, lesions of the mucous membranes, skin and eyes.
With avitaminosis A, the skin becomes dry, flaky, secondary putrefactive and purulent processes begin. Also affects the epithelium of the mucous membrane of the respiratory, digestive, urogenital apparatus. A characteristic damage of the eyeball develops - dryness of the cornea of the eye due to plugging of the lacrimal canal, the cover of which also undergoes keratinization. The eyeball is not washed with a tear that has a bactericidal property, and putrefactive microorganisms develop on the surface of the cornea. As a result, there are swelling, inflammation of the conjunctiva, softening and ulceration and cornea. A specific symptom of hypovitaminosis A is chicken or night blindness, expressed in the loss of the ability to distinguish objects in the twilight, although in the daytime the person sees normally.
Products that contain vitamin A
The need for an organism in vitamin A should be provided by a third of products that contain retinol:
and two thirds of products that contain carotene:
Using products containing vitamins of group A, it should be borne in mind that the vitamin activity of carotene in foods is three times lower than that of retinol (vitamin A), so fresh fruits and vegetables need to eat three times more than cooked products of animal origin.