Vitamin A – This name is determined by a group of related chemicals, which have biological activity of transretinol. Provitamin A are some carotenoid dyes. Beta-carotene plays a special role in this respect.
Absorption of retinol, and especially carotenes, is facilitated in the presence of bile fats and acids. The blood has specific retinol transporting proteins, However, carotenes are associated with lipoproteids. Vitamin A supplies accumulate in the liver and with normal shipping the amount of them is sufficient to cover the needs of the system in the period to 6 months.
Vitamin A is, among others, necessary to maintain the correct operation of the eye and mucous membranes.
One of the early symptoms of this vitamin deficit is the impairment of vision at dusk. dust blindness.
Currently, it is recommended to provide an adult per day in Poland. 5000 international units of vitamin A, which corresponds to ok. 1000 NG retinol assuming, That 2500 j.m. comes from retinol and the next 2500 j.m. with beta-carotene. Fao/Who gives, that the lower dose is sufficient, in namely 750 ng vitamins A day. This norm does not change for hard -working people and for climate zones. Is worth knowing, that all infections and high temperature levels reduce the amount of vitamin A in blood serum.
It should also be emphasized, that vitamin A in higher doses is toxic. The overdose of vitamin A in the form of pharmacological preparations is particularly dangerous (The conclusion is itself - you have to take under strict medical supervision). Natural, Carotenes contained in plant products do not show any toxic properties. Vitamin A in form, which can be toxic, Occurs only in animal products, such as butter, egg yolk, fish oils, liver.
In the vegetarian diet, vitamin A deficiencies do not occur. The richest in vitamin A or its provitamins are: :carrot, Green lettuce, spinach, tomatoes.
Is worth knowing, that the source of retinol is also vitaminized margarine.