Key points
Biotin is a key metabolic helper. Biotin (vitamin B7) is needed by enzymes that build and break down fatty acids and help make glucose from other substances (Burgerstein, Handbuch Nährstoffe 2015, p. 81–82). The norm for adults is 30–60 µg a day (Burgerstein, Handbuch Nährstoffe 2015, p. 83).
If you are deficient, it may help. In 18 reported cases (hair and nails), improvement was noted after biotin, but these people had an underlying cause: biotin deficiency or a disease of the hair and nails (Patel DP Skin Appendage Disord 2017. PMID 28879195).
It may help brittle nails. In 8 patients with brittle nails, nail thickness increased by 25% (Colombo VE J Am Acad Dermatol 1990. PMID 2273113), and in another small analysis 22 of 35 people noticed improvement (Hochman LG Cutis 1993. PMID 8477615).
No benefit shown in healthy people. For healthy people, data on a benefit of biotin for hair are insufficient (Patel DP Skin Appendage Disord 2017. PMID 28879195).
High doses can distort lab tests. In 6 healthy adults, 10 mg of biotin a day for a week distorted 9 of 23 biotin-based tests (Li D JAMA 2017. PMID 28973622). The author of one case report believes that a break of at least 2 days should be enough to avoid a gross error (Barbesino G Thyroid 2016. PMID 27043844).
What biotin does
The norm is small: 30 µg a day under the 1998 US recommendations and 30–60 µg under the 2000 recommendations of Germany, Austria and Switzerland (Burgerstein, Handbuch Nährstoffe 2015, p. 83). During pregnancy and breastfeeding the need increases, and antibiotics impair biotin absorption (Burgerstein, Handbuch Nährstoffe 2015, p. 82).
Over-the-counter supplements often contain 10 mg (10,000 µg) (Li D JAMA 2017. PMID 28973622) — about 330 times more than the 30 µg norm.
When biotin is really lacking
Overt biotin deficiency with symptoms is rare. According to some data, marginal deficiency develops in a notable share of women during a normal pregnancy (Mock DM J Nutr 2017. PMID 28701385).
The causes are too little biotin in the diet, interactions with medicines, possibly faster breakdown during pregnancy and in smokers, and reduced activity of the enzyme biotinidase and other proteins of biotin metabolism. The signs are dermatitis, hair loss, seizures, reduced muscle tone and impaired coordination (Zempleni J Expert Rev Endocrinol Metab 2008. PMID 19727438).
Hair and nails: what is known
Hair. The review authors believe that biotin may help with its deficiency, brittle nail syndrome or “uncombable hair”; such cases are uncommon, and for healthy people the evidence is insufficient (Patel DP Skin Appendage Disord 2017. PMID 28879195).
If your hair is falling out, check other causes too, such as iron stores: Ferritin and hair loss: how much iron is needed.
Nails. In 8 patients with brittle nails whose nails were examined before and after a course of biotin, nail thickness increased by 25%; in 14 whose course did not match the timing of sample collection, by 7%; the nails split less (Colombo VE J Am Acad Dermatol 1990. PMID 2273113).
When all visits over six months at a nail disease clinic were reviewed, 44 patients with brittle nails who had been prescribed biotin were found. Of the 35 who took it daily, 22 (63%) noted improvement, and 13 (37%) had no change (Hochman LG Cutis 1993. PMID 8477615). The analysis is retrospective, the assessment is subjective, and there is no placebo group.
Why biotin distorts lab tests
Many lab tests use the strong bond between biotin and the protein streptavidin, and excess biotin in the blood interferes with it. In the experiment with 10 mg a day, tests without this bond were not affected, while in the affected ones some results were falsely high and others falsely low (Li D JAMA 2017. PMID 28973622).
Thyroid. In a patient with multiple sclerosis on very high doses of biotin, free thyroxine (T4) and triiodothyronine (T3) were sharply elevated, thyroid-stimulating hormone (TSH) was suppressed and TSH receptor antibodies were elevated — as in severe Graves’ disease (autoimmune hyperthyroidism), although there were no symptoms. After biotin was temporarily stopped, the tests returned to normal (Barbesino G Thyroid 2016. PMID 27043844). More about TSH in the article TSH is a pituitary hormone, not a thyroid hormone.
Heart. Blood biotin above 81.8 nmol/L (20 ng/mL) can lower the result of one of the high-sensitivity tests for troponin T, the protein used to recognize a heart attack. Such a level was found in 1 of 797 samples (0.13%) from patients with suspected acute coronary syndrome (a heart attack or the threat of one), and in a sample from a US laboratory network in 15 of 2,023 (0.74%). The risk of missing a heart attack because of biotin was estimated as extremely low — 0.026%; the study was carried out with the participation of the test manufacturer (Mumma B Clin Chem Lab Med 2020. PMID 32804676).
How common is it. Since 2016, the FDA (the US agency that regulates medicines) has received 92 reports of probable lab test distortion by biotin; a person may not even know they are taking biotin (Bowen R Clin Biochem 2019. PMID 31473202). In a survey of 1,944 patients, 7.7% were taking biotin, and in 7.4% of 1,442 emergency department patients the blood level was 40.9 nmol/L (10 ng/mL) or higher — the lowest known interference threshold for one manufacturer’s tests (Katzman BM Clin Biochem 2018. PMID 30036510).
How long to stop before a test
The author of one case report believes that a break of at least 2 days should be enough to avoid a gross error (Barbesino G Thyroid 2016. PMID 27043844). Tell your doctor and the laboratory that you take biotin. If the result does not match how you feel, the test is repeated after stopping biotin or on a different analyzer (Bowen R Clin Biochem 2019. PMID 31473202).
What the studies showed
| What was studied | Who took part | Result |
|---|---|---|
| Biotin for hair and nails, review, 2017 | 18 reported cases | Improvement noted after biotin; the people had an underlying cause; evidence for healthy people is insufficient |
| Brittle nails, 1990 | 22 patients and 10 people with healthy nails | Nail thickness +25% in 8 patients; +7% in 14 whose course did not match the timing of sample collection |
| Brittle nails, retrospective, 1993 | 35 patients | Improvement in 22 (63%), no change in 13 |
| 10 mg of biotin a day for 7 days, 2017 | 6 healthy adults, 37 tests | Distortion in 9 of 23 streptavidin–biotin tests, 0 of 14 others |
| Biotin use by patients, 2018 | 1,944 questionnaires, 1,442 blood samples | 7.7% were taking it; level of 40.9 nmol/L (10 ng/mL) or higher in 7.4% |
| Troponin T and biotin, 2020 | 797 samples with suspected heart attack and 2,023 samples from a US laboratory network | High biotin in 0.13% and 0.74%; risk of missing a heart attack 0.026%; with the participation of the test manufacturer |
Not everything is equally proven: for healthy people, a benefit of biotin for hair has not been shown — this does not mean there definitely is none, but suitable studies are lacking (Patel DP Skin Appendage Disord 2017. PMID 28879195); the nail studies are small and have no placebo group (Colombo VE J Am Acad Dermatol 1990. PMID 2273113); (Hochman LG Cutis 1993. PMID 8477615).
Who should be more careful
- If you take biotin or a “hair, skin and nails” complex, tell your doctor before any lab tests, especially thyroid hormone, sex hormone and troponin tests (Bowen R Clin Biochem 2019. PMID 31473202).
- If tests show hyperthyroidism but you feel no different, think of biotin before starting treatment (Barbesino G Thyroid 2016. PMID 27043844).
- With chest pain, do not delay calling an ambulance, and tell the doctor that you take biotin: this will help interpret the troponin test correctly.
- During pregnancy and breastfeeding the need for biotin is higher (Burgerstein, Handbuch Nährstoffe 2015, p. 82), so it is better to choose vitamins with your doctor.
Bottom line
Biotin is needed for metabolism, and if you are deficient in it, supplements may help hair and nails. Biotin helped brittle nails in small studies, while no benefit has been shown for healthy hair. The main practical rule: high doses of biotin can distort lab tests, so it is stopped before a blood test and the doctor is told. You can sort out hair loss, brittle nails and strange test results at a consultation.
This material is for information only and does not replace a doctor’s consultation. The decision to take biotin and how long to pause it before tests is made by a doctor.
