Vitamin B7 (Biotin) - Nutrition

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What is Vitamin B7 (Biotin)?

Vitamin B7, also called biotin, is an essential water-soluble vitamin. Biotin is actively transported across the intestinal mucosa, with minimal passive diffusion, and is typically found as free biotin in plasma. Biotin is not stored in the body and is freely filtered by the renal tubules.

Why is it Important?

Biotin’s only known function is as a component of carboxylase enzymes which features in energy metabolism. Under normal circumstances endogenous production of biotin by bacterial synthesis in the gastrointestinal tract is sufficient to meet metabolic requirements.

Roles in the Body

Biotin is an essential component of 4 carboxylase enzymes[1]:

  1. Pyruvate carboxylase, which converts pyruvate to oxaloacetate (OAA) during carbohydrate metabolism;
  2. Acetyl CoA carboxylase, which is the rate limiting enzyme step in conversion of acetyl CoA to malonyl CoA in fatty acid synthesis;
  3. Propionyl CoA carboxylase, which carboxylates propionyl CoA (from amino acid, fatty acid or carbohydrate metabolism) into methylmalonyl CoA; and
  4. 3-methylcrotonyl CoA carboxylase, which functions in the catabolic pathway for leucine.

Consequences of Biotin Deficiency

Naturally occurring biotin deficiencies have not been reported unless accompanied by the feeding of raw egg white. Egg white contains a compound called avadin, which irreversibly binds biotin, making it unavailable for physiologic use.

Dogs:

Dogs fed raw egg white develop hyperkeratosis of the skin and scaling[2].

Cats:

Kittens fed raw egg white developed excessive accumulation of ocular, nasal, and salivary secretion, alopecia, achromotrichia, skin scaling, weight loss, and diarrhoea[3].

Toxicity

There are no published reports of biotin toxicity in dogs and cats[2]; excess intake is freely filtered through the renal tubules.

Dietary Sources

High concentrations of naturally occurring biotin are found in meats, dairy products, grains, and pulses (e.g. legumes). Because endogenous microbial synthesis is normally adequate, a dietary supply of biotin is not required. However supplementation may be necessary in situations where intestinal microbial synthesis is compromised, such as long term administration of anti-bacterial agents.

Diagnosing Biotin Deficiency

Dietary history of feeding raw eggs or raw egg whites. Diagnosis is also made on clinical signs consistent with deficiency and evaluation of diet (either direct measurement or computer evaluation for biotin).

References

  1. Sweetman L. Pantothenic Acid and Biotin. In Biochemical and physiological aspects of human nutrition. 2000 Philadelphia, PA: WB Saunders Company p.529-540.
  2. 2.0 2.1 National Research Council (NRC). Vitamins. In Nutrient Requirements for Dogs and Cats. 2006 Washington, DC: National Academies Press p.230-231.
  3. Carey CJ and Morris JG. Biotin deficiency in the cat and its effect on hepatic propionyl CoA carboxylase. J Nutr 1977;107:330-334.



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