Key points
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[4]) — 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[6]).
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[7]).
Hair and nails: what is known
If your hair is falling out, check other causes too, such as iron stores: Ferritin and hair loss: how much iron is needed.
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[3]). 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[4]).
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[5]). 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[9]).
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[1]); the nail studies are small and have no placebo group (Colombo VE J Am Acad Dermatol 1990. PMID 2273113[2]); (Hochman LG Cutis 1993. PMID 8477615[3]).
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[9]).
- If tests show hyperthyroidism but you feel no different, think of biotin before starting treatment (Barbesino G Thyroid 2016. PMID 27043844[5]).
- 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.
References
- Patel DP Skin Appendage Disord 2017. PMID 28879195
- Colombo VE J Am Acad Dermatol 1990. PMID 2273113
- Hochman LG Cutis 1993. PMID 8477615
- Li D JAMA 2017. PMID 28973622
- Barbesino G Thyroid 2016. PMID 27043844
- Mock DM J Nutr 2017. PMID 28701385
- Zempleni J Expert Rev Endocrinol Metab 2008. PMID 19727438
- Mumma B Clin Chem Lab Med 2020. PMID 32804676
- Bowen R Clin Biochem 2019. PMID 31473202
- Katzman BM Clin Biochem 2018. PMID 30036510
Key facts
- Overt biotin deficiency with symptoms is rare; according to some data, marginal deficiency develops in a notable share of pregnant women (Mock DM, J Nutr 2017).
- In 18 reported cases (hair and nails), improvement was noted after biotin, but these people had an underlying cause; evidence for healthy people is insufficient (Patel DP, Skin Appendage Disord 2017).
- In 8 patients with brittle nails, nail plate thickness increased by 25% after a course of biotin (Colombo VE, J Am Acad Dermatol 1990).
- In 6 healthy adults, 10 mg of biotin a day for a week distorted 9 of 23 tests based on the streptavidin–biotin bond (Li D, JAMA 2017).
- High doses of biotin can produce a suppressed thyroid-stimulating hormone (TSH) and high free thyroxine (T4) and triiodothyronine (T3), as in hyperthyroidism; 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).
