Vitamins

Vitamins are organic substances required in small quantities for metabolic processes by human organism. Term “vitamin” does not include other essential nutrients, such as dietetic minerals, fatty acids or indispensable amino acids.
Vitamins are biomolecules, that act as catalysts or substrata (carriers of catalysts) in the chemical reactions. As catalysts, vitamins become part of ferments and are called cofactors. As an example, vitamin K is a part of proteases, involved in blood coagulation. Vitamins also work as coferments, that carry free radicals and chemical groups between ferments. Vitamins serve as hormones (vitamin D), antioxidants (vitamin E), cells mediators as well as regulators of tissue growth and differentiation (vitamin A)

Vitamins are classified into water soluble (C and B complex) or fat soluble (A, D, E and K).
Fat soluble vitamins are absorbed into the blood in the complex with fats and are carried to the liver where they are stored. Some diseases that affect intestine,including malabsorption syndrome may result in insufficiency of fat soluble vitamins.
Water soluble vitamins, such as B vitamin complex or vitamin C and are stored in organism for certain period of time and then are excreted by the kidneys. With the exception of Vitamin B12, that is stored in the liver.