This paper examines the metabolism of thiamine (Vitamin B1), a water-soluble vitamin essential to carbohydrate metabolism and numerous cellular functions. It covers dietary sources, recommended intake levels, intestinal absorption mechanisms, and the role of thiamine transporters encoded by the SLC19A2 gene. The paper explains how thiamine is converted to its active form, thiamine pyrophosphate (TPP), and its function in key metabolic pathways including the pyruvate dehydrogenase complex, the citric acid cycle, and the pentose phosphate pathway. It also addresses the consequences of thiamine deficiency — including Korsakoff's Syndrome, Alzheimer's disease, and diabetes — and outlines the clinical options for thiamine administration.
Thiamine is a water-soluble vitamin — Vitamin B1 — that serves as a cofactor for enzymes with mitochondrial localization. Because it is not endogenously synthesized, it must be obtained through dietary sources such as beef, poultry, nuts, and cereals. Thiamine plays a critical role in oxidative and nonoxidative carbohydrate metabolism during the energy transformation process. Additional functions include an antioxidant effect on neurotrophins, suppression of oxidative stress-induced activation, a critical role in activating the immune system, signaling and maintenance in cells, and cell uptake mechanisms.
Intestinal enzyme phosphatase hydrolyzes thiamine into a free form that is absorbed in the small intestines. The phosphorylated form is stored in the heart, kidneys, brain, and liver. Thiamine has a half-life of 1 to 12 hours and can be stored in the body for 14 to 18 days. Consequently, regular dietary intake is necessary to prevent the development of a deficiency.
The recommended thiamine intake differs with age and gender, but a standard intake of 1.2 mg/day for men and 1.1 mg/day for women is advised, with increments to 1.4 mg/day during pregnancy and lactation, respectively. Regular intake is imperative to maintain correct thiamine levels in the body. The intestinal uptake of thiamine is regulated by a molecular mechanism involving thiamine transporters 1 and 2, which are products of the Solute Carrier Family 19 Member 2 (SLC19A2) gene. SLC19A2 encodes thiamine transporter 1 (THTR1) across cell membranes. Homozygous mutation of this gene causes thiamine-responsive megaloblastic anemia, sensorineural deafness, and diabetes. Therefore, thiamine deficiency results in impaired insulin secretion in conjunction with mitochondrial dysfunction, cell cycle arrest, and loss of immunity against oxidative stress.
In the blood, the thiamine diphosphokinase enzyme converts thiamine into its active form, thiamine pyrophosphate (TPP), which plays different roles during metabolic processes including glucose metabolism, the Krebs cycle, the pentose phosphate pathway, and amino acid metabolism.
During the preparation of food, a considerable loss of thiamine occurs through cooking or heat-induced food processing. In countries where there is a large dependence on processed foods, thiamine deficiency is a widespread concern. Processed foods have a high caloric density but lack adequate micronutrient content relative to recommended dietary guidelines. This condition is referred to as high-calorie malnutrition. More than 29% of obese individuals who undergo bariatric surgery are thiamine deficient. Different forms of thiamine play distinct roles in intercellular synthesis. Thiamine monophosphate contributes to the intercellular synthesis of thiamine triphosphate and diphosphate.
"Neurological roles and deficiency-related disorders"
"Routes of thiamine administration and clinical use"
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