Vitamin B7 (Biotin)
VitaminFoundational
An essential cofactor you almost certainly get enough of. The hair-and-nails supplement mostly causes wrong blood test results.
At a glance
Essential · don't supplement
-
Helps process fat, sugar and protein
Powers the carboxylase enzymes in all three pathways.
why ↓
-
Hair and nails, only if you're deficient
Every case where it helped involved an underlying deficiency or disorder.
why ↓
Strong human evidenceEarly / limited
How to take it
- About 30 mcg a day. A normal diet covers it.
- Eggs (cooked), liver, salmon, beef, sunflower seeds
Watch out
- High-dose biotin skews thyroid, hormone and heart blood tests. Stop it before a blood draw.
- Lots of raw egg white can cause deficiency
Signs you're low
- Thinning hair, rash around the eyes, nose and mouth
- Tingling, low mood, lethargy
The Research
Mechanisms, studies and evidence grades for each claim above.
Biotin is the covalently bound cofactor for five carboxylase enzymes, each of which adds a CO₂ group at a key metabolic junction: acetyl-CoA carboxylase (the committed step of fatty acid synthesis), pyruvate carboxylase (the first step of making new glucose, and a refill point for the TCA cycle), and propionyl-CoA and methylcrotonyl-CoA carboxylase (breakdown of odd-chain fats and several amino acids, including leucine). Biotin also takes part in histone modification. (Strong — core enzymology)
↑ back to summary
Deficiency
Dietary deficiency is rare. Adequate intake is commonly cited around 30 mcg/day for adults, and gut bacteria contribute some. The known causes are specific:
- Raw egg white. It contains avidin, a protein that binds biotin so tightly it can't be absorbed. Habitually eating large amounts of raw egg white can cause deficiency; cooking denatures avidin. (Whole cooked eggs are a good biotin source; the yolk is where the biotin is.)
- Biotinidase deficiency, an inherited inability to recycle biotin, which is included in newborn screening and treated with lifelong supplementation.3
- Long-term anticonvulsant use and some malabsorption states.
Deficiency presents as thinning hair, a scaly red rash around the eyes, nose and mouth, conjunctivitis, and neurological symptoms (lethargy, depression, tingling). (Strong)
↑ back to summary
Hair and nails, only if you're deficient
Biotin's hair-and-nail reputation comes from the deficiency picture above: if hair falls out when biotin is missing, supplementing should grow hair. A systematic review of the literature found 18 reported cases in which biotin improved hair or nails — and in every one, the patient had an underlying cause (inherited or acquired biotin deficiency, or conditions like brittle nail syndrome or uncombable hair). The authors found insufficient evidence for supplementation in healthy people.1 (Early — case reports only; no RCT support in non-deficient people)
↑ back to summary
The lab-test problem
Caution: many clinical blood tests use biotin–streptavidin binding as part of the assay, and excess biotin in the blood interferes with it. In a study of six healthy adults taking 10 mg/day (a common hair-supplement dose, over 300× the adequate intake) for one week, 9 of 23 biotin-based assays gave wrong results — some falsely high, some falsely low — across thyroid tests (TSH, T4, T3), PTH, prolactin, NT-proBNP, and vitamin D.
2 False thyroid results can mimic hyperthyroidism, and the FDA has warned that biotin interference with troponin tests can cause a missed heart attack. Tell whoever orders bloodwork if you take biotin, and stop high-dose products for a few days beforehand.
Top foods
- Beef liver
- Eggs (cooked)
- Salmon
- Beef
- Sunflower seeds
↑ back to summary
References
- Patel DP, Swink SM, Castelo-Soccio L. A review of the use of biotin for hair loss. Skin Appendage Disord 2017. PMID 28879195
- Li D et al. Association of biotin ingestion with performance of hormone and nonhormone assays in healthy adults. JAMA 2017. PMID 28973622
- Biotinidase Deficiency. GeneReviews. PMID 20301497