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==What is Vitamin B1 (Thiamin)?==

==What is Vitamin B1 (Thiamin)?==

Vitamin B₁, also called '''thiamin''', is an '''essential water-soluble vitamin''' used in glucose and amino acid metabolism and energy production. Thiamin is readily absorbed across the intestinal mucosa via active carrier-mediated transport as well as via passive diffusion. Once in the enterocyte, thiamin can either be converted to thiamin pyrophosphate (TPP) for immediate use in the cell, or transported as thiamin into the portal circulation to the liver. Once in the liver it is rapidly distributed throughout the body. Thiamin can be found as a free vitamin within the plasma, but is largely found as part of TPP within erythrocytes and leukocytes. '''Thiamin is not stored in the body and is freely filtered by the renal tubules'''.

Vitamin B₁, also called '''thiamin''', is an '''essential water-soluble vitamin''' used in glucose and amino acid metabolism and energy production. Thiamin is readily absorbed across the intestinal mucosa via [[Active Transport - Physiology|active carrier-mediated transport]] as well as via [[Diffusion - Physiology|passive diffusion]]. Once in the enterocyte, thiamin can either be converted to thiamin pyrophosphate (TPP) for immediate use in the cell, or transported as thiamin into the portal circulation to the [[Liver - Anatomy & Physiology|liver]]. Once in the liver it is rapidly distributed throughout the body. Thiamin can be found as a free vitamin within the [[plasma]], but is largely found as part of TPP within [[Erythrocyte|erythrocytes]] and [[leukocytes]]. '''Thiamin is not stored in the body and is freely filtered by the Nephron Microscopic Anatomy#Proximal Tubule|renal tubules]]'''.

==Why is it Important?==

==Why is it Important?==

==Roles in the Body==

==Roles in the Body==

Thiamin (as TPP) is responsible for the decarboxylation of α-ketoacids and acyl-CoA derivatives during amino acid and glucose metabolism. The TPP-dependant enzyme transketolase is also involved in metabolism of glucose and ribose synthesis via the pentose phosphate pathway.  

Thiamin (as TPP) is responsible for the decarboxylation of α-ketoacids and acyl-CoA derivatives during amino acid and glucose metabolism. The TPP-dependant enzyme transketolase is also involved in metabolism of glucose and ribose synthesis via the pentose phosphate pathway.  

Thiamin is one of the essential nutrients involved with the clinical sequelae of refeeding syndrome<ref>Mehanna HM, et al. Refeeding syndrome: what it is, and how to prevent and treat it. BMJ 2008;336:1495-1498.</ref>. Refeeding syndrome can occurs when chronically starved animals are given a large bolus of readily absorbed carbohydrates without adequate amount of rate-limiting essential nutrients, specifically thiamin, potassium, and magnesium. The intracellular shift of these nutrients can cause rapid and profound clinical signs, leading to death if untreated.

Thiamin is one of the essential nutrients involved with the clinical sequelae of refeeding syndrome<ref>Mehanna HM, et al. Refeeding syndrome: what it is, and how to prevent and treat it. BMJ 2008;336:1495-1498.</ref>. Refeeding syndrome can occurs when chronically starved animals are given a large bolus of readily absorbed carbohydrates without adequate amount of rate-limiting essential nutrients, specifically thiamin, [[Potassium - Nutrition|potassium]], and [[Magnesium - Nutrition|magnesium]]. The intracellular shift of these nutrients can cause rapid and profound clinical signs, leading to death if untreated.

==Consequences of Thiamin Deficiency==

==Consequences of Thiamin Deficiency==

====Cats:====  

====Cats:====  

Cats fed thiamin deficient diet develop '''anorexia initially, followed by progressive clinical signs of neurological involvement in 1-2 weeks'''. The neurological signs include flexion of the head, impaired proprioception and righting reflexes, seizures, progressive weakness, and death<ref name="NRC"/>. Kittens fed thiamin deficient diets can also develop ataxia and mydriasis. Bilaterally symmetric grey matter necrosis is also a feature of thiamin deficiency in cats and kittens<ref>Moon S, et al. Clinical signs, MRI features, and outcomes of two cats with thiamine deficiency secondary to diet change. J Vet Sci 2013;14:499-502.</ref>.

Cats fed thiamin deficient diet develop '''anorexia initially, followed by progressive clinical signs of neurological involvement in 1-2 weeks'''. The neurological signs include flexion of the head, impaired proprioception and righting reflexes, seizures, progressive weakness, and death<ref name="NRC"/>. Kittens fed thiamin deficient diets can also develop ataxia and mydriasis. Bilaterally symmetric grey matter necrosis is also a feature of thiamin deficiency in cats and kittens<ref>Moon S, et al. Clinical signs, MRI features, and outcomes of two cats with thiamine deficiency secondary to diet change. J Vet Sci 2013;14:499-502.</ref>.

Conditions associated with diuresis (e.g., chronic disease, such as renal disease or diabetes, or therapeutic intervention, such as intravenous fluids or increased water intake to manage lower urinary disease) can result in increased loss of thiamin and may increase daily requirements. Patients on chronic haemodialysis are also at an increased risk for developing a deficiency.  

Conditions associated with diuresis (e.g., chronic disease, such as renal disease or [[Diabetes Insipidus|diabetes]], or therapeutic intervention, such as intravenous fluids or increased water intake to manage [[Cystitis|lower urinary disease]]) can result in increased loss of thiamin and may increase daily requirements. Patients on chronic haemodialysis are also at an increased risk for developing a deficiency.  

Thiamin deficiencies can also occur due to low dietary intake, presence of compounds in food that directly antagonise thiamin, and vitamin degradation during cooking. Thiaminases are present in certain freshwater and marine fishes, but this enzyme is readily denatured with heating<ref name="NRC"/>. Additionally sulphite preservatives in meats can degrade thiamin resulting in clinical signs of deficiency<ref>Studdert VP and Labuc RH. Thiamin deficiency in cats and dogs associated with feeding meat preserved with sulphur dioxide. Aust Vet J 1991;68:54-57.</ref>. Thiamin is particularly sensitive to degradation with increased temperature especially under alkaline conditions, such as can occur during canned foods production. This higher rate of thiamin degradation requires commercial pet food manufacturers to monitor and supplement thiamin according to expected losses.  

Thiamin deficiencies can also occur due to low dietary intake, presence of compounds in food that directly antagonise thiamin, and vitamin degradation during cooking. Thiaminases are present in certain freshwater and marine fishes, but this enzyme is readily denatured with heating<ref name="NRC"/>. Additionally sulphite preservatives in meats can degrade thiamin resulting in clinical signs of deficiency<ref>Studdert VP and Labuc RH. Thiamin deficiency in cats and dogs associated with feeding meat preserved with sulphur dioxide. Aust Vet J 1991;68:54-57.</ref>. Thiamin is particularly sensitive to degradation with increased temperature especially under alkaline conditions, such as can occur during canned foods production. This higher rate of thiamin degradation requires commercial pet food manufacturers to monitor and supplement thiamin according to expected losses.  

==Toxicity==

==Toxicity==

No reports of toxicity in dogs and cats with excess oral intake. High doses given intravenously to dogs can result in dramatic and potentially fatal hypotension<ref name="NRC"/>, while high doses given intravenously to cats can result in neuromuscular blockade and associated sign of weakness<ref>Freye E and Agoutin H. The action of vitamin B1 (thiamine) on the cardiovascular system of the cat. Biomedicine 1978;28:315-319.</ref>.

No reports of toxicity in dogs and cats with excess oral intake. High doses given intravenously to dogs can result in dramatic and potentially fatal hypotension<ref name="NRC"/>, while high doses given intravenously to cats can result in neuromuscular blockade and associated signs of weakness<ref>Freye E and Agoutin H. The action of vitamin B1 (thiamine) on the cardiovascular system of the cat. Biomedicine 1978;28:315-319.</ref>.

==Dietary Sources==

==Dietary Sources==

[[Category:Vitamins]]

[[Category:Vitamins]]

[[Category:To Do - Nutrition]]

[[Category:To Do - Nutrition]]

[[Category:To Do - Nutrition GGP]]

[[Category:To Do - Nutrition preMars]]