Biotin

What does biotin do?

Biotin is a water-soluble vitamin from the B vitamin group. According to NIH, it is a cofactor of five carboxylase enzymes (propionyl-CoA carboxylase, pyruvate carboxylase, methylcrotonyl-CoA carboxylase, acetyl-CoA carboxylase 1 and 2) and provides critical steps in the metabolism of fatty acids, glucose and amino acids. It also has roles in histone modifications, gene regulation and cell signaling. EFSA likewise states that biotin is the cofactor of the carboxylases required for fatty acid synthesis, breakdown of branched-chain amino acids and gluconeogenesis. ^{[1] [2]}

This function does not mean that biotin is a “beauty vitamin” or an “energy vitamin.” Biotin is needed for an enzyme to work; there is no controlled study showing that more biotin improves hair or nails in someone whose level is adequate. This page keeps the function (role) separate from the benefit of extra supplements.

How much biotin is needed daily?

Because the evidence for biotin is insufficient, the Food and Nutrition Board (FNB) in the US has set only an “adequate intake” (AI) rather than a recommended daily allowance (RDA). The AI values reported by NIH are 30 µg per day for adults and pregnant women and 35 µg for breastfeeding women. The FNB set these values by starting from the amount of biotin infants receive from breast milk and adapting it to other age groups according to body weight. ^[1]

EFSA, on the other hand, set the AI for adults at 40 µg per day; this value also applies to pregnant women, and for breastfeeding women an additional 5 µg is proposed to cover the loss in breast milk. Because the values of the two organizations were derived with different methods and different data, one is not the “right” or “wrong” version of the other. ^[2]

NIH states that there are no nationally representative intake data in the US, but that in other Western populations mean intake from foods is about 35–70 µg per day, and that most people therefore get adequate biotin. ^[1]

According to NIH, the FNB has not set a tolerable upper intake level (UL) for biotin because there is no evidence of toxicity at high intakes in humans. In several studies, no side effects were seen with 10–50 mg of biotin per day. This does not mean that a high dose is harmless in every respect: the laboratory interaction below occurs at these intake levels. ^[1]

When does biotin deficiency occur?

NIH states that biotin deficiency is rare and that severe deficiency has never been reported in healthy people eating a normal mixed diet. EFSA also states that diet-related biotin deficiency is rare. Symptoms progress insidiously; according to NIH, thinning hair (progressing to loss of body hair), a scaly red rash around the eyes, nose and mouth, conjunctivitis, seizures, skin infection, brittle nails, depression in adults, lethargy and paresthesias of the hands and feet can be part of this picture. ^{[1] [2]}

The reverse of this list is not true: having hair loss or brittle nails is not evidence of deficiency; most of these findings arise from other causes. The groups NIH lists as at risk of deficiency are as follows: ^[1]

• People with biotinidase deficiency. This is a rare autosomal recessive disease; the body cannot release free biotin, and deficiency develops even if intake is normal. If untreated, neurological and skin symptoms appear. Because lifelong oral biotin from birth can prevent these symptoms, newborns are screened in the US and many countries.
• People who use alcohol chronically. Chronic alcohol exposure impairs biotin absorption; plasma biotin is low in 15% of people with chronic alcoholism.
• Pregnant and breastfeeding women. NIH reports that marginal deficiency develops in at least one-third of pregnant women despite normal intake; it also states that further research is needed for its clinical meaning.
• People on long-term antiepileptics. In 264 people with epilepsy, anticonvulsant treatment for at least 1 year was associated with markedly lower serum biotin than in controls. NIH lists carbamazepine, primidone, phenytoin and phenobarbital among the drugs used in this study.
• People who regularly eat a lot of raw egg white. Avidin in raw egg white binds biotin tightly and blocks its absorption; cooking inactivates avidin.

In Türkiye, biotinidase deficiency was added to the National Newborn Screening Program of the Ministry of Health General Directorate of Public Health in October 2008. According to the General Directorate (HSGM), phenylketonuria screening began in 1987, and the program was launched on December 25, 2006 as the National Newborn Screening Program with the addition of congenital hypothyroidism screening. ^[7]

Does biotin work for hair and nails?

Because hair loss and brittle nails are among the symptoms of biotin deficiency, supplements are often marketed as hair, skin and nail products. NIH states that these claims are supported “at best by a few case reports and small studies.” ^[1]

Hair. The review by Patel and colleagues (a PubMed search for case reports and randomized studies) found 18 reported cases in which biotin was used for hair and nail changes. In all the cases, the patient had an underlying condition leading to poor hair or nail growth, and clinical improvement was reported in all. The authors noted that biotin may be beneficial in acquired and inherited biotin deficiency and in conditions such as brittle nail syndrome or uncombable hair, but that these cases are rare and that there is not enough evidence for supplements in healthy people. NIH, for its part, lists only cases in children for hair health: marked improvement in hair health in 3–4 months with 3–5 mg of biotin per day in children with uncombable hair syndrome. ^{[3] [1]}

Nails. NIH reports three small studies examining biotin in brittle nails; none of the three has a placebo group, and the participants’ baseline biotin status was not reported. In one of them (22 women with brittle, splitting or soft nails and 10 healthy volunteers; 2.5 mg of biotin per day, 6–15 months), nail thickness increased by 25% in 8 patients whose nail samples were taken before and immediately after biotin; in 14 patients whose samples were taken 2–4 months after treatment began and 1–4 months after it ended, the increase was 7% and was not statistically significant. In the second study, improvement was reported in 41 of 45 patients (91%), and in the third (retrospective) study in 22 of 35 patients (63%). The studies are old and small; for this reason, the level of evidence is weak. ^[1]

Summary: biotin has a place in a person with deficiency or with certain rare nail-hair diseases; it has not been shown to lengthen or strengthen hair in a healthy person.

Does biotin supplementation distort blood tests?

Yes; this is the most important practical risk of biotin. According to NIH, very high biotin intake can disrupt tests that use biotin-streptavidin technology and are widely used to measure hormones (such as thyroid hormone) and other substances such as 25-hydroxyvitamin D, producing falsely normal or falsely abnormal results. ^[1]

Controlled data. In the study by Li and colleagues in JAMA, healthy adults (2 women and 4 men, mean age 38) took 10 mg of biotin per day for 7 days; this is a dose the study describes as “common in over-the-counter supplements,” and it is about 333 times the AI in the US. Interference was found in 9 of 23 biotin-containing tests (39%) and in none of 14 tests that do not contain biotin. Of competitive immunoassays, 5/8 gave falsely high results, and of sandwich immunoassays, 4/15 gave falsely low results. The study is small, non-randomized and preliminary; a later correction of the paper has been published (JAMA 2017). ^[4]

Cases. NIH reports several case reports that led to a false diagnosis of Graves disease and severe hyperthyroidism in patients taking 10–300 mg of biotin per day; among them are six children taking high doses because of an inherited metabolic disease. Even a single 10 mg dose disrupted thyroid tests done within 24 hours. According to NIH, a falsely low TSH can lead to a diagnosis of thyrotoxicosis, and a falsely low NT-proBNP to a missed heart failure. ^[1]

Troponin. The FDA’s troponin page states that biotin disrupts troponin tests used in diagnosing heart attack and that the FDA continues to receive adverse event reports of falsely low troponin results due to biotin interference. According to NIH, the FDA reported that a patient taking a high amount of biotin died after a falsely low troponin result on a test susceptible to biotin interference. According to the FDA, some manufacturers have succeeded in reducing this interference in their tests, and some have not. ^{[5] [1]}

The practical conclusion is informational only: NIH reports that the FDA recommends that health care workers ask patients whether they take supplements containing biotin and consider biotin interference as a possible source of error if results do not fit the clinical picture. For this reason, it is important to tell staff before a test and in the emergency department that biotin or biotin-containing products (B-complex, hair-nail products, multivitamins) are being used. ^[1]

Does high-dose biotin work for multiple sclerosis?

Drug-level high-dose biotin (MD1003) has been investigated in progressive multiple sclerosis. SPI2 is a randomized, double-blind, placebo-controlled phase 3 trial conducted at 90 centers in 13 countries: 642 participants aged 18–65 with a diagnosis of primary or secondary progressive MS took 100 mg of biotin three times daily or placebo. On the primary endpoint (improvement on EDSS or the timed 25-foot walk (TW25) at month 12, confirmed at month 15), improvement occurred in 39 of 326 people (12%) in the MD1003 group and in 29 of 316 people (9%) in the placebo group (OR 1.35; 95% CI 0.81–2.26). The authors concluded that there was no significant improvement and that, given the potential to distort laboratory tests, MD1003 could not be recommended for treating progressive MS. The daily dose of 300 mg is about 10,000 times the AI in the US (30 µg) and is not the same as everyday supplements. In the study, MD1003 also led to false laboratory results in tests that use biotinylated antibodies. ^[6]

Does biotin affect blood sugar?

The systematic review and meta-analysis examining biotin in patients with type 2 diabetes pooled five randomized controlled trials (445 participants); biotin had been given for 28–90 days. The mean difference in fasting glucose was −1.21 mmol/L, but the 95% confidence interval was between −2.73 and 0.31, including zero. The mean difference was −0.22 mmol/L (−0.25 to −0.19) for total cholesterol and −0.59 mmol/L (−1.21 to 0.03; includes zero) for triglycerides. Although the authors wrote in their abstract that biotin “significantly reduced” fasting glucose, total cholesterol and triglycerides, the confidence intervals they gave for fasting glucose and triglycerides include zero; only the small fall in total cholesterol has an interval that does not include zero. No significant benefit was found for insulin; there was not enough evidence to draw a conclusion for HbA1c, LDL, HDL and VLDL. The studies cover only people with type 2 diabetes; they give no information on the effect in healthy people and do not replace diabetes treatment. ^[8]

Evidence table: claim, population and limits

Safety, interactions and the product label

For drug interactions with biotin, NIH mentions antiepileptics: these drugs can lower biotin status by increasing biotin catabolism and reducing its absorption from the gut. This does not mean a supplement is needed; monitoring and the decision belong to the physician. NIH states that biotin is found only in biotin-containing products, in B-complex mixtures and in some multivitamin-mineral products; the amount varies by product and is read from the label. ^[1]

In pregnancy and breastfeeding, when tests are planned or when there is a chronic disease, the personal decision is made with a physician. This guide does not recommend a personal dose.

Common misunderstandings about biotin

• “Biotin makes hair grow longer.” Not shown in healthy people; the evidence rests on cases with deficiency or an underlying disease. ^[3]
• “It is a water-soluble vitamin, so excess does no harm.” No UL has been set, but high doses can distort tests and at least one death has been reported to the FDA. ^[1]
• “Biotin deficiency is very common.” NIH states that deficiency is rare. ^[1]
• “Raw egg is healthy.” Avidin in raw egg white blocks biotin absorption; cooking removes this effect. ^[1]

What to consider together with biotin

Biotin is a single B vitamin; its relationship with other B vitamins is covered in the B-complex guide, B12 in the B12 guide, and folate in the folic acid guide.