[1][2][3] It is involved in a wide range of metabolic processes, both in humans and in other organisms, primarily related to the utilization of fats, carbohydrates, and amino acids.

At that time there was insufficient information to establish estimated average requirement or recommended dietary allowance, terms that exist for most vitamins.

[9] The European Food Safety Authority (EFSA) also identifies AIs, setting values at 40 μg/day for adults, pregnancy at 40 μg/day, and breastfeeding at 45 μg/day.

[11] For US food and dietary supplement labeling purposes, the amount in a serving is expressed as a percent of daily value.

[1][3] According to the Global Fortification Data Exchange, biotin deficiency is so rare that no countries require that foods be fortified.

KAPA is transported from plant peroxisomes to mitochondria where it is converted to 7,8-diaminopelargonic acid (DAPA) with the help of the enzyme, BioA.

Subclinical deficiency can cause mild symptoms, such as hair thinning, brittle fingernails, or skin rash, typically on the face.

[4][26] Neonatal screening for biotinidase deficiency started in the United States in 1984, with many countries now also testing for this genetic disorder at birth.

[1] Holocarboxylase synthetase deficiency prevents the body's cells from using biotin effectively and thus interferes with multiple carboxylase reactions.

[26] Biochemical and clinical manifestations of any of these metabolic disorders can include ketolactic acidosis, organic aciduria, hyperammonemia, rash, hypotonia, seizures, developmental delay, alopecia and coma.

[4] Chemically modified versions of biotin are widely used throughout the biotechnology industry to isolate proteins and non-protein compounds for biochemical assays.

[33] Because egg-derived avidin binds strongly to biotin with a dissociation constant Kd ≈ 10−15 M,[34] biotinylated compounds of interest can be isolated from a sample by exploiting this highly stable interaction.

First, the chemically modified biotin reagents are bound to the targeted compounds in a solution via a process called biotinylation.

[34] When people are ingesting high levels of biotin in dietary supplements, a consequence can be clinically significant interference with diagnostic blood tests that use biotin-streptavidin technology.

Overconsumption of 5 mg/day or higher causes elevated concentration in plasma that interferes with biotin-streptavidin immunoassays in an unpredictable manner.

[29] In 1916, W. G. Bateman observed that a diet high in raw egg whites caused toxic symptoms in dogs, cats, rabbits, and humans.

[39] By 1927, scientists such as Margarete Boas and Helen Parsons had performed experiments demonstrating the symptoms associated with "egg-white injury."

They had found that rats fed large amounts of egg whites as their only protein source exhibited neurological dysfunction, hair loss, dermatitis, and eventually, death.

[40][41] In 1936, Fritz Kögl and Benno Tönnis documented isolating a yeast growth factor in a journal article titled "Darstellung von krystallisiertem biotin aus eigelb."

Hungarian scientist Paul Gyorgy began investigating the factor responsible for egg-white injury in 1933 and in 1939, was successful in identifying what he called "Vitamin H" (the H represents Haar und Haut, German for 'hair and skin').

[51] High-dose biotin (300 mg/day = 10,000 times adequate intake) has been used in clinical trials for treatment of multiple sclerosis, a demyelinating autoimmune disease.

[37][38] The hypothesis is that biotin may promote remyelination of the myelin sheath of nerve cells, slowing or even reversing neurodegeneration.

The proposed mechanisms are that biotin activates acetyl-CoA carboxylase, a key rate-limiting enzyme during the synthesis of myelin, and by reducing axonal hypoxia through enhanced energy production.

[37][38] Clinical trial results are mixed; a 2019 review concluded that a further investigation of the association between multiple sclerosis symptoms and biotin should be undertaken,[37] whereas two 2020 reviews of a larger number of clinical trials reported no consistent evidence for benefits,[52] and some evidence for increased disease activity and higher risk of relapse.

[53] In the United States, biotin is promoted as a dietary supplement for strengthening hair and fingernails, though scientific data supporting these outcomes in humans are very weak.

[3][54][55] A review of the fingernails literature reported brittle nail improvement as evidence from two pre-1990 clinical trials that had administered an oral dietary supplement of 2.5 mg/day for several months, without a placebo control comparison group.

[58] Consequences of lameness include less food consumption, lower milk production, and increased veterinary treatment costs.

The discussion speculated that this could be an indirect consequence of improved hoof health or a direct effect on milk production.

[60] For horses, conditions such as chronic laminitis, cracked hooves, or dry, brittle feet incapable of holding shoes are a common problem.