Biotin

What it is

Biotin, also called vitamin B7, is a water-soluble vitamin that serves as a cofactor for the carboxylase enzymes involved in fat, glucose and amino acid metabolism. True deficiency is rare, but it causes hair thinning and skin changes, which is why biotin is widely sold for hair and skin. Doses on the market span a very wide range, from nutritional amounts to far larger ones.

Used for

• Hair loss
• Skin

What to know while taking it

It can be taken with or without food, and excess is cleared in the urine rather than stored. The point that matters most is analytical rather than clinical: biotin interferes with many laboratory immunoassays that use biotin-streptavidin binding, which can push thyroid, hormone and cardiac troponin results falsely high or falsely low depending on the assay design. Because of this, the laboratory should be told biotin is being used, and it is normally paused for a period before blood is drawn, on the lab's or doctor's instruction.

When to see a doctor

Any lab result that does not fit how a person feels, especially a thyroid or troponin value, should be flagged to a doctor as a possible biotin artefact before it is acted on. Hair loss that continues despite supplementation deserves a proper cause to be looked for.

Worth knowing

• Distorts several lab assays