Vitamin A
This does not only refer to a single molecule, but to a group of related molecules that constitute vitamin A: retinol, retinal, and provitamins: α-, β- and γ-carotene, and other carotenoids. β-carotene is the most biologically active.
It is important for maintaining the epithelium, hormone secretion, cell growth in all organs, and quality of vision. Deficiency causes night blindness, changes in the skin and digestive system, weakness of the body, bone deformities, and drying and softening of the cornea.
Vitamin A is soluble in fats and oils. Its action is mainly due to binding to specific nuclear receptors, thus later affecting the synthesis of specific proteins. It is important for controlling the growth and development of epithelial tissue and participates in the formation of visual pigment. Therefore, its deficiencies cause various disorders, from night blindness to certain skin disorders. In addition, a significant effect of vitamin A results from its antioxidant properties, i.e., that it binds to free radicals in the body.
It is important, however, to know that vitamin A can cause the greatest problems in the body if ingested in excessive amounts. A larger amount of vitamin A than prescribed in the body is called hypervitaminosis. This leads to numerous toxic effects accompanied by disorders in digestion, skin, bones, and joints. Ingesting even larger amounts leads to acute poisoning, the symptoms of which are skin peeling, fatigue, insomnia, edema, etc. Since a large excess of β-carotene can no longer be converted into vitamin A, this excess accumulates in the epidermis, giving it a yellowish color.
Sources of Vitamins
Vitamin A or β-carotene is found in foods of animal and plant origin. In foods of animal origin, this vitamin is in the form of retinol and dehydratinol, while in foods of plant origin, it is found as a mixture of provitamins: α-carotene, crypto-carotene, β-carotene, and γ-carotene.
It is found in carrots, green vegetables, butter, cheese and dairy products, liver, egg yolk, fish oil, parsley, eel and other fish, and apricots.
Recommended Daily Dose
The daily requirement for an adult is about 700-900 µg; during pregnancy and lactation, it is 1200 µg (= 1.2 mg), but direct intake of vitamin A is prohibited at that time due to the risk of overdose! Liver consumption during pregnancy is contraindicated.
Children from 1 to 8 years: 300-400 µg
Boys aged 9 to 18 years: 600 to 900 µg
Adult men: 900 µg
Girls between 9 and 18 years: 600-700 µg
Adult women: 700 µg
During pregnancy: 750-770 µg
During lactation: 1.2-1.3 mg
Vitamin E, zinc, and selenium are necessary for its absorption and optimal incorporation. Steaming vegetables in a little water, short-term cooking, frying, and grilling help its absorption.