Currently, vitamins can be characterized as low molecular weight organic compounds, which, being a necessary part of the food present in it in extremely small quantities compared to Its main components. Vitamins are divided into two groups: 1) vitamins, fat soluble 2) vitamins, water soluble 1. Vitamins, fat-soluble vitamin A (retinol, akseroftol) Vitamin A has an effect on growth rights, improves skin, promotes resistance to infection, provides growth and development of epithelial cells, is a part of the visual pigment retinal rod eyes – rhodopsin and visual pigment cones – iodopsin. These pigments regulate the dark adapted eye. Lack of vitamin A leads to poor vision in low light ('night blindness'). Manifestations of hypovitaminosis A: The skin becomes dry and rough on arms and calves feet, flakes, keratinization of hair follicles makes it rough. Nails are dry and dull. Frequently observed conjunctivitis, characterized by dryness of the cornea – xerophthalmia.
There is also a weight loss (up to depletion) in children – growth retardation. Symptoms of excess vitamin A: drowsiness, fatigue, headache, facial flushing, nausea, vomiting, irritability, frustration gait, pain in the bones of the lower extremities. May observed worsening of cholelithiasis and chronic pancreatitis. Vitamin A is found only in foods of animal origin (fish oil, milk fat, butter, cream, cottage cheese, egg yolk, fat, liver and fat of other organs – heart, brain). However, in the human body (in the intestinal wall and liver) vitamin A may be formed from some of the pigments, called carotenes, which are widespread in plant foods.