VITAMIN B1 AND ITS STATUS IN VEGETARIANS AND VEGANS

Vitamin B1 is a water-soluble vitamin whose alternative name is thiamine or thiamin. The metabolically active form of vitamin B1 is thiamin diphos-phate, also known as thiamin pyrophosphate. Thiamin diphosphate is a coenzyme in the pyruvate dehydrogenase complex and in the Krebs cycle. Thus, it is directly involved in catabolism. In addition, vitamin B1 also takes part in the pentose phosphate shunt, which contributes to the synthesis of nucleotides and their derivatives. Similarly, thiamin diphosphate plays an important role in myelin synthesis, amino acid metabolism, and the metabo-lism of neurotransmitters and hormones. There is also evidence for its direct regulation of ion channel activity. Lack of vitamin B1 affects all organs and tissues, but the earliest manifestations of its deficiency are found in the nervous system. There are several reasons for this. Firstly, the nervous tissue is extremely and continuously dependent on glucose oxidation, which can be disrupted in case of insuffi-ciency of the pyruvate dehydrogenase complex. Secondly, myelin production is interrupted. Thirdly, there is an imbalance of neurotransmitters. The fourth reason is the high activity of transmembrane ion-exchange processes in the nervous tissue. All these lead to damage to the central and periph-eral nervous system and, in severe cases, the development of beriberi or Wernicke-Korsakoff syndrome. B1 hypervitaminosis is an unlikely event. The hydrophilic thiamin diphosphate is rapidly excreted through the urine with an increase in its serum con-centrations. In addition, the intake of large amounts of thiamin with food significantly reduces its intestinal absorption. As thiamin is relatively safe even in high quantities, the high vitamin B1 dose is used to treat symptoms of chronic cluster headaches and some neurodegenerative diseases. Thiamin is quite evenly distributed in both animal- and plant-derived products. Its highest concentrations are found in the outer layer of cereals, leg-umes, seeds, or nuts. As a result, most studies show that thiamin intake is higher in vegans and vegetarians than in omnivores. But, with regard to the status of vitamin B1, not everything is so crystal clear. There are not many studies done on this topic to date. The lack of general consensus on a single accepted methodology for assessing the status of vitamin B1 seems to be the main hurdle. Although most of the data indicate a better supply of vitamin B1 in vegans and vegetarians, further research and standardization of methods are still needed.