Vitamin B1 (Thiamin) - Nutrition

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.

Why is it Important?

Thiamin is required for formation of (TPP), a coenzyme used during energy production, and is required by transketolase enzymes used during glucose metabolism. Cats require approximately 3x the amount of thiamin on a metabolic body weight basis relative to dogs.

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 is one of the essential nutrients involved with the clinical sequelae of refeeding syndrome. 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.

Consequences of Thiamin Deficiency

Dogs:

Puppies fed thiamin deficient diets experience slow growth, inappetance, weight loss, coprophagia, neurological abnormalities (circling, torticollis, ataxia, and central nervous system depression) and sudden death. Dogs with acute thiamin deficiency develop bilaterally symmetric grey matter necrosis; chronic deficiencies can progress to myocardial and peripheral nerve degeneration.

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. 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. 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. 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. Additionally sulphite preservatives in meats can degrade thiamin resulting in clinical signs of deficiency. 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

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, while high doses given intravenously to cats can result in neuromuscular blockade and associated sign of weakness.

Dietary Sources

Thiamin is naturally occurring in nuts and seeds, muscle and organ meats (especially liver and kidney), yeast, and pulses (e.g., legumes). It is also supplemented into all commercially-prepared complete and balanced dog and cat foods.

Diagnosing Thiamin Deficiency

Diagnosis of thiamine deficiency is based on measurement of low erythrocyte transketolase activity or low plasma thiamine phosphorylated esters serum retinol, though not routinely tested through veterinary reference laboratories. Submission of samples to a human reference laboratory may be possible, though often concurrent submission of normal reference samples is required. Magnetic resonance imaging (MRI) images show changes consistent with thiamine deficient grey matter degeneration. Diagnosis is also made on clinical signs consistent with deficiency, evaluation of diet, and response to parenteral thiamine supplementation.