Biological Properties of Vitamins of the B-Complex, Part 1: Vitamins B 1 , B 2 , B 3 , and B 5 .

This review summarizes the current knowledge on essential vitamins B ₁ , B ₂ , B ₃ , and B ₅ . These B-complex vitamins must be taken from diet, with the exception of vitamin B ₃ , that can also be synthetized from amino acid tryptophan. All of these vitamins are water soluble, which determines their main properties, namely: they are partly lost when food is washed or boiled since they migrate to the water; the requirement of membrane transporters for their permeation into the cells; and their safety since any excess is rapidly eliminated via the kidney. The therapeutic use of B-complex vitamins is mostly limited to hypovitaminoses or similar conditions, but, as they are generally very safe, they have also been examined in other pathological conditions. Nicotinic acid, a form of vitamin B ₃ , is the only exception because it is a known hypolipidemic agent in gram doses. The article also sums up: (i) the current methods for detection of the vitamins of the B-complex in biological fluids; (ii) the food and other sources of these vitamins including the effect of common processing and storage methods on their content; and (iii) their physiological function.