Vitamin B7 (Biotin)

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Vitamin B7

Good sources: Cheese, egg yolks, milk, fish, peanut butter, & liver.

DRI: 20-30 mg/d

Functions:  Biotin is required for proper metabolism of fats and carbohydrates. Biotin-dependent enzymes catalyze the addition of carboxyl groups (COO-) from bicarbonate, for use in fatty acid biosynthesis, gluconeogenesis, lipogenesis, propionate metabolism and leucine catabolism.  Biotin is a co-enzyme in glucose production and fat synthesis.

Cofactor Functions:

  • Cofactor to acetyl-CoA carboxylase, needed for fatty acid metabolism
  • Cofactor to pyruvate carboxylase, an enzyme needed for gluconeogenesis
  • Cofactor to methylcrotonyl-CoA carboxylase, which metabolizes leucine
  • Cofactor to propionyl-CoA carboxylase (also called holocarboxylase synthetase), which metabolizes amino acids and cholesterol
  • Cofactor for fatty acid synthesis (specifically for elongating the fatty acid chain)

All Other Functions:

  • The protein in egg whites (avidin) binds to biotin preventing its absorption so those who consume raw egg are at increased risk of biotin deficiency
  • Essential cofactor for four carboxylase enzymes in the mitochondria
  • Common indications of biotin deficiency include brittle nails, alopecia and dermatitis due to impaired fatty acid synthesis from reduced biotin-dependent carboxylases enzymes (particularly acetyl-CoA carboxylase)
  • Decreases synthesis of cytokines (interleukin-1 b and interleukin-2)
  • Decreases proliferation of peripheral blood mononuclear cells
  • Affects gene transcription (over 2,000 biotin dependent genes have been identifies)
  • Biotin deficiency in pregnancy may be teratogenic
  • Stimulates glucose-induced insulin secretion in pancreatic beta cells
  • Induces glucokinase, an enzyme needed for cells to use glucose
  • Accelerates glycolysis in liver and pancreas
  • Studies indicate in can reduce triglycerides and improve glycemic control
  • Biotin deficiency has induced depression in animal and human studies
  • Animal studies show induced biotin deficiency presents clinically as fatigue
  • Reduces blood pressure by activating the enzyme guanylate cyclase which in turn activates cGMP (cyclic guanosine monophosphate)
  • Anticonvulsant therapy such as phenobarbital and valproic acid may induce biotin deficiency

Deficiencies:  Symptoms of biotin deficiency include erythematous exfoliative dermatitis, thinning hair, fatigue, irritability, mild depression, somnolence, muscle pains, anorexia, nausea, mild anemia. Infants with seborrheic dermatitis, Leiner’s disease or alopecia may indicate a biotin deficiency, along with symptoms of ketoacidosis, poor feeding, vomiting, lethargy, coma and developmental retardation. Dietary symptoms include fatigue, dry skin, body hair loss, nausea, loss of appetite and mild depression.

Those at risk for biotin deficiency include: persons consuming excessive amounts of raw egg whites, inherited disorders of biotin metabolism, extended total parenteral nutrition (biotin-free), loss of enteric gut microflora from antibiotic

therapy or altered gut motility, pregnant and lactating women, antiepileptic drug therapy, alcoholics, trauma (burns and surgery), elderly, malabsorption (especially achlorhydria).

Toxicities: None known