Editing Thiamine (section)

==Absorption, metabolism and excretion==
In the upper small intestine, thiamine phosphate esters present in food are hydrolyzed by alkaline [[phosphatase]] enzymes.<ref>{{cite book|doi=10.1016/B978-0-323-66162-1.00010-X |chapter=Thiamine |title=Present Knowledge in Nutrition |date=2020 |pages=171–188 |isbn=978-0-323-66162-1 | vauthors = Bettendorff L }}</ref> At low concentrations (<2 μmol l−1), the absorption process is carrier-mediated.<ref name="Laird"/> At higher concentrations, absorption also occurs via [[passive diffusion]].<ref name="Laird"/><ref name=PKIN2020B1/> Active transport can be inhibited by alcohol consumption or by [[folate deficiency]].<ref name="Mahan"/>

The majority of thiamine in [[serum (blood)|serum]] is circulating bound to [[albumin]],<ref name="Laird">{{cite book|doi=10.1016/B978-0-12-801238-3.00233-6|quote=Thiamine is absorbed through the jejunum (small intestine) via two mechanisms: active transport or passive diffusion. At low concentrations (<2 μmol l−1), the process is carrier-mediated active transport. Two main thiamine transporters ThTR1 and ThTr2 are essential for absorption and the process is thought to be regulated by an intracellular calcium/calmodulin-mediated pathway and by the actual extracellular circulating concentration of thiamine itself. The majority of thiamine in serum is protein bound to albumin with over 90% contained within erythrocytes. Cellular uptake occurs by active transport and passive diffusion through thiamine transporters ThTr1 and ThTr2. |chapter=Water-Soluble Vitamins and Essential Nutrients |title=Reference Module in Biomedical Sciences |date=2014 |isbn=978-0-12-801238-3 | vauthors = Laird E, Molloy A }}</ref> with over ({{Percentage|90}}) in [[erythrocyte]]s (red blood cells),<ref name="Laird"/> and is delivered to cells with high metabolic needs—particularly those in the brain, liver, pancreas, heart, and skeletal and smooth muscles, including cardiac muscle cells.<ref name=whitfield/> A specific binding protein called thiamine-binding protein has been identified in rat serum and is believed to be a hormone-regulated carrier protein important for tissue distribution of thiamine.<ref name="Combs"/> Uptake of thiamine by cells of the blood and other tissues occurs via active transport and passive diffusion.<ref name="Mahan"/><ref name="Laird"/> Two members of the family of transporter proteins encoded by the genes [[Thiamine transporter 1|SLC19A2]] and [[Thiamine transporter 2|SLC19A3]] are capable of thiamine transport.<ref>{{cite book|doi=10.1016/B978-0-12-810387-6.00003-4 |chapter=Mitochondria, Thiamine, and Autonomic Dysfunction |title=Thiamine Deficiency Disease, Dysautonomia, and High Calorie Malnutrition |date=2017 |pages=59–103 |isbn=978-0-12-810387-6 | vauthors = Lonsdale D, Marrs C }}</ref><ref name="Laird"/><ref name=Lons2006/> In some tissues, thiamine uptake and secretion appear to be mediated by a Na<sup>+</sup>-dependent transporter and a transcellular proton gradient.<ref name="Combs"/>

Human storage of thiamine is about 25 to 50&nbsp;mg,<ref name=ods/><ref name="pmid30281514"/> with the greatest concentrations in liver,<ref name=ods/><ref name="uptake"/> skeletal muscle, heart, brain, and kidneys.<ref name="pmid30281514">{{cite journal |vauthors=Chandrakumar A, Bhardwaj A, 't Jong GW |title=Review of thiamine deficiency disorders: Wernicke encephalopathy and Korsakoff psychosis |journal=J Basic Clin Physiol Pharmacol |volume=30 |issue=2 |pages=153–162 |date=October 2018 |pmid=30281514 |doi=10.1515/jbcpp-2018-0075}}</ref><ref name="uptake">{{cite book|doi=10.1016/B978-0-12-381980-2.00010-4 |chapter=Thiamin |title=The Vitamins |date=2012 |pages=261–276 |isbn=978-0-12-381980-2 | vauthors = Combs GF }}</ref> ThMP and free (unphosphorylated) thiamine are present in plasma, milk, [[cerebrospinal fluid]], and, it is presumed, all [[extracellular fluid]]. Unlike the highly phosphorylated forms of thiamine, ThMP and free thiamine are capable of crossing cell membranes. Calcium and magnesium have been shown to affect the distribution of thiamine in the body and [[magnesium deficiency]] has been shown to aggravate thiamine deficiency.<ref name=Lons2006/> Thiamine contents in human tissues are less than those of other species.<ref name="Combs"/><ref>{{cite journal | vauthors = Bettendorff L, Mastrogiacomo F, Kish SJ, Grisar T | title = Thiamine, thiamine phosphates, and their metabolizing enzymes in human brain |journal = Journal of Neurochemistry |volume = 66 |issue = 1 |pages = 250–8 | date = January 1996 |pmid = 8522961 |doi = 10.1046/j.1471-4159.1996.66010250.x | s2cid = 7161882 }}</ref> The [[half-life]] of thiamine content stored in tissues of human body is about 9-18 days,<ref name="pmid30281514"/> while after intake in high doses, the half-life of thiamine in circulating blood is about one to 12 hours.<ref name=whitfield/> Additionally, thiamine pyrophosphate derived from pyrimidines supports lipid synthesis and adipogenesis, highlighting its role in energy storage and cellular differentiation.<ref name=lpi/><ref name="Sahu2024"/>

Thiamine and its metabolites (2-methyl-4-amino-5-pyrimidine carboxylic acid, 4-methyl-thiazole-5-acetic acid, and others) are excreted principally in the urine.<ref name=PKIN2020B1/>

===Interference===
The [[bioavailability]] of thiamine in foods can be interfered with in a variety of ways. [[Sulfite]]s, added to foods as a preservative,<ref>{{cite book | vauthors = McGuire M, Beerman KA | title = Nutritional Sciences: From Fundamentals to Foods. | date = 2007 | location = California | publisher = Thomas Wadsworth }}</ref> will attack thiamine at the methylene bridge, cleaving the pyrimidine ring from the thiazole ring. The rate of this reaction is increased under acidic conditions.<ref name="Combs"/> Thiamine is degraded by thermolabile [[thiaminase]]s present in some species of fish, shellfish and other foods.<ref name="Mahan"/> The pupae of an African silk worm, ''[[Anaphe venata]]'', is a traditional food in Nigeria. Consumption leads to thiamine deficiency.<ref>{{cite journal |vauthors=Nishimune T, Watanabe Y, Okazaki H, Akai H |title=Thiamin is decomposed due to Anaphe spp. entomophagy in seasonal ataxia patients in Nigeria |journal=J. Nutr. |volume=130 |pages=1625–8 |year=2000 |issue=6 |doi=10.1093/jn/130.6.1625 |pmid=10827220 |doi-access=free }}</ref> Older literature reported that in Thailand, consumption of fermented, uncooked fish caused thiamine deficiency, but either abstaining from eating the fish or heating it first reversed the deficiency.<ref name="Vimokesant1975">{{cite journal |vauthors=Vimokesant SL, Hilker DM, Nakornchai S, Rungruangsak K, Dhanamitta S |title=Effects of betel nut and fermented fish on the thiamin status of northeastern Thais |journal=Am J Clin Nutr |volume=28 |issue=12 |pages=1458–63 |date=December 1975 |pmid=803009 |doi=10.1093/ajcn/28.12.1458}}</ref> In ruminants, intestinal bacteria synthesize thiamine and thiaminases. The bacterial thiaminases are cell surface enzymes that must dissociate from the cell membrane before being activated; the dissociation can occur in ruminants under [[acidosis|acidotic conditions]]. In [[dairy cattle|dairy cows]], over-feeding with grain causes subacute ruminal acidosis and increased ruminal bacteria thiaminase release, resulting in thiamine deficiency.<ref>{{cite journal |vauthors=Pan X, Nan X, Yang L, Jiang L, Xiong B |title=Thiamine status, metabolism and application in dairy cows: a review |journal=Br J Nutr |volume=120 |issue=5 |pages=491–9 |date=September 2018 |pmid=29986774 |doi=10.1017/S0007114518001666|s2cid=51606809 |doi-access=free }}</ref>

From reports on two small studies conducted in Thailand, chewing slices of [[areca nut]] wrapped in [[betel]] leaves and chewing tea leaves reduced food thiamine bioavailability by a mechanism that may involve [[tannins]].<ref name="Vimokesant1975"/><ref>{{cite journal |vauthors=Vimokesant S, Kunjara S, Rungruangsak K, Nakornchai S, Panijpan B |title=Beriberi caused by antithiamin factors in food and its prevention |journal=Ann N Y Acad Sci |volume=378 |issue= 1|pages=123–36 |date=1982 |pmid=7044221 |doi=10.1111/j.1749-6632.1982.tb31191.x|bibcode=1982NYASA.378..123V |s2cid=40854060 }}</ref>

Bariatric surgery for weight loss is known to interfere with vitamin absorption.<ref>{{cite journal |vauthors=Nunes R, Santos-Sousa H, Vieira S, Nogueiro J, Bouça-Machado R, Pereira A, Carneiro S, Costa-Pinho A, Lima-da-Costa E, Preto J |title=Vitamin B Complex Deficiency After Roux-en-Y Gastric Bypass and Sleeve Gastrectomy-a Systematic Review and Meta-Analysis |journal=Obes Surg |volume=32 |issue=3 |pages=873–91 |date=March 2022 |pmid=34982396 |doi=10.1007/s11695-021-05783-2|s2cid=245655046 }}</ref> A meta-analysis reported that {{Percentage|27}} of people who underwent bariatric surgeries experience vitamin B<sub>1</sub> deficiency.<ref>{{cite journal |vauthors=Bahardoust M, Eghbali F, Shahmiri SS, Alijanpour A, Yarigholi F, Valizadeh R, Madankan A, Pouraskari AB, Ashtarinezhad B, Farokhi H, Sarafraz H, Khanafshar E |title=B1 Vitamin Deficiency After Bariatric Surgery, Prevalence, and Symptoms: a Systematic Review and Meta-analysis |journal=Obes Surg |volume=32 |issue=9 |pages=3104–12 |date=September 2022 |pmid=35776243 |doi=10.1007/s11695-022-06178-7|s2cid=250149680 }}</ref>