Biotin (vitamin B7)

Biotin, also called vitamin B7 or vitamin H, is a water-soluble B vitamin with sulphur in its molecule. It is found in egg yolk, offal, nuts, pulses and oats, mostly bound to protein; the enzyme biotinidase releases it in the gut and recycles it in the body. Gut bacteria also produce biotin, but how much of it is absorbed is not precisely known. The stores are small. Biotin is measured in blood, in the test catalogue together with vitamin A, vitamin B3 and vitamin B5.

What biotin does in the body

Biotin is firmly bound to five enzymes, the carboxylases. They attach carbon dioxide units to other molecules and thereby link several metabolic pathways: acetyl-CoA carboxylase starts the building of fatty acids, and pyruvate carboxylase supplies material for making new glucose in the liver and replenishes the citric acid cycle. Propionyl-CoA and methylcrotonyl-CoA carboxylase break down certain amino acids and odd-chain fatty acids. Fatty acids are needed, among other things, for the skin barrier and cell membranes. In addition, biotin is bound to histones in the cell nucleus and is involved in regulating genes. Skin, hair and nails react sensitively because their cells renew themselves quickly.

Low biotin – what happens in the body?

When biotin is lacking, the carboxylases work more slowly. Fewer fatty acids are built, and breakdown products such as 3-hydroxyisovaleric acid build up and appear in urine. This shows first in skin and hair: thinning hair up to hair loss, a scaly red rash around the eyes, nose and mouth, and brittle nails. Exhaustion, low mood and tingling in the arms and legs may follow. A deficiency arises, for example, with congenital biotinidase deficiency, with long-term consumption of large amounts of raw egg white – the protein avidin binds biotin in the gut –, with high alcohol consumption, with some medicines against seizures and with impaired absorption in the gut. In pregnancy, increased consumption has been observed in studies.

High biotin – what happens in the body?

Excess biotin is excreted via the kidneys; no harmful effects from biotin in food are known. High blood levels almost always come from preparations for skin, hair and nails, which often contain many times the usual intake. This matters mainly for other laboratory values: many measuring methods use the tight binding between biotin and the protein streptavidin. A lot of biotin in the blood interferes with these tests and can make values appear falsely high or falsely low – this has been described, for example, for thyroid values such as TSH and fT4, for troponin and for some hormones. A high biotin value therefore sometimes explains inconsistent results in other reports.

The interpretation is given in your report.