Biotin is a benign B vitamin. Deficiency, uncommon in the general population, causes alopecia. Patients on long-term anticonvulsants should be supplemented.
[DFM ] Letter Key
Description
- Biotin is a water-soluble B vitamin necessary for energy metabolism.
- It is an essential cofactor for four CO2-fixing carboxylase enzymes, including acetyl-CoA carboxylase, pyruvate carboxylase, propionyl-CoA carboxylase, and
-methylcrotonyl CoA carboxylase. Each of these catalyzes a critical step in intermediary metabolism. The U.S. population consumes about 28 to 42 µg/day of biotin, and the Western European population consumes 50 to 100 µg/day. - It is not stored in the body.
Food Sources
- Biotin is widely distributed in foods.
- Good food sources include liver (about 100 µg/100 g), egg yolk (about 50 µg/100 g), yeast (about 100 µg/100 g), soybeans (about 60 µg/100 g), cereals, legumes (especially sprouted legumes), and nuts.
- The only vegetables that are significant sources of biotin are mushrooms, cauliflower, and sea vegetables (1).
- Intestinal bacteria produce a significant amount of biotin (2).
Main Functions/Pharmacokinetics
- Biotin acts as a coenzyme in four carboxylases that are involved in "fixation" of CO2 in animal cells, gluconeogenesis and reversal of glycolysis, fatty acid synthesis, and leucine degradation.
- Oral doses of biotin are 100% bioavailable, even in large doses, but administration of a single large dose may increase renal losses (3).
[Outline]
[CO ] Letter Key
Clinical Trials
- Brittle nails
- A trial of biotin (2.5 mg p.o. q.d.) in women with brittle nails found improved morphology and a 25% increase in nail thickness, assessed by electron microscopy (4).
Other Claimed Benefits/Actions
Increases hair growth
[Outline]
[DF
L ] Letter Key
Deficiency Signs and Symptoms
- Scaly dermatitis (especially around the eyes, nose, and mouth).
- Alopecia, often with loss of hair color.
- Depression.
- Lassitude, lethargy.
- Hallucinations.
- Paresthesias.
- In infants: periorificial dermatitis, conjunctivitis, alopecia (including eyebrows and eyelashes), hypotonia, withdrawn affect, developmental delay.
- Biotin deficiency is uncommon in normal populations; it can be induced by biotinidase deficiency, excessive intake of raw egg white, malabsorption syndromes, or prolonged use of total parenteral nutrition (TPN) without biotin supplementation. Biotinidase deficiency, an inborn error of metabolism, results in an inability to release biotin from degraded carboxylases. This recycling mechanism is important for biotin conservation, so biotin deficiency can result (5).
- "Egg white injury" disease is biotin deficiency induced by consumption of raw egg white, which contains the glycoprotein avidin (which binds biotin at four sites and prevents its absorption) (6).
- Marginal biotin deficiency is not uncommon during pregnancy. In several animals, biotin deficiency is teratogenic at levels that do not obviously affect the pregnant animal (7).
Factors Decreasing Availability/Absorption
- Holoenzyme synthetase deficiency
- Biotinidase deficiency
- Propionicacidemia
- -methylcrotonyl glycinuria
- Alcoholism
- Inflammatory bowel disease
- Malabsorption syndromes
- Excessive intake of raw egg white
- Anticonvulsants
- Antibiotics
Laboratory Tests
- Blood biotin levels are not an early or sensitive indicator of impaired biotin status. Biotin deficiency results in increased 3-hydroxy-isovaleric acid excretion, decreased bisnorbiotin excretion, and accumulation of odd-chain fatty acids in plasma. Biotin deficiency is best established retrospectively based on whether symptoms improve with biotin administration (8).
- Whole blood biotin (normal values) 200 to 500 pg/mL.
- Urinary biotin (normal values) 6 to 100 µg/24 hours.
[Outline]
Q: Are the symptoms of biotin deficiency and biotinidase deficiency the same?
A: Not quite. Although both result in periorificial dermatitis, alopecia, conjunctivitis, ataxia, and developmental delay, biotinidase deficiency can also cause seizures, irreversible neurosensory hearing loss, and optic atrophy, which are not seen in biotin deficiency (there is one case of cerebral atrophy and an apparent stretching of the optic nerve in a patient with biotin deficiency) (8). Biotinidase deficiency may cause additional problems because of the breakdown of biotin-dependent enzymes, thus causing accumulation of metabolites.
Q: Why do anticonvulsants induce biotin deficiency?
A: There are several mechanisms that may account for this; the process may be multifactorial. Primidone and carbamazepine inhibit biotin uptake from the intestine. Phenobarbital, phenytoin, and carbamazepine displace biotin from biotinidase, which may affect transport, cellular uptake, or availability of biotin. Increased excretion of metabolites suggest that anticonvulsants may also accelerate biotin catabolism (8).
Q: Is there a connection between biotin deficiency and sudden infant death syndrome (SIDS)?
A: Two researchers have hypothesized that biotin deficiency could be related to SIDS via a pathogenic mechanism similar to that which causes a fatal hypoglycemic disease in chicks. Apparently hepatic levels of biotin are lower in the livers of babies who died of SIDS when compared with those who died from other causes. This is only a hypothesis; much more work would be needed to establish whether or not there is a connection (8).