Vitamin B7 (Biotin)

1. Introduction: Product, Chemical Basics, and Mechanism of Action

Vitamin B7, commonly known as Biotin or Vitamin H, is a water-soluble B-complex vitamin essential for human health. As an essential nutrient, it must be obtained through the diet, as the human body cannot synthesize it in sufficient quantities, although gut bacteria may produce some [1].

Chemically, biotin is a heterocyclic, sulfur-containing compound (Formula: C10H16N2O3S). It is characterized by an ureido ring fused with a tetrahydrothiophene ring, with a valeric acid side chain attached to one of the carbon atoms of the tetrahydrothiophene ring.

The primary mechanism of action of biotin is its function as a covalently bound cofactor for five critical carboxylase enzymes [1, 3]. These enzymes are responsible for catalyzing key steps in fundamental metabolic pathways. By acting as a carrier for carbon dioxide, biotin facilitates the carboxylation reactions necessary for the metabolism of fatty acids, glucose, and amino acids [1]. Beyond its role in energy metabolism, biotin also plays a significant role in gene regulation, cell signaling, and histone modifications [1].

2. Chemical Composition and Key Bioactive Roles

Biotin’s biological activity is intrinsically linked to its role as a prosthetic group for carboxylase enzymes. The key bioactive roles and associated compounds are summarized below.

Bioactive Role	Associated Carboxylase Enzyme	Metabolic Function
Gluconeogenesis	Pyruvate Carboxylase	Converts pyruvate to oxaloacetate, a critical step in glucose synthesis.
Fatty Acid Synthesis	Acetyl-CoA Carboxylase 1 & 2	Catalyzes the conversion of acetyl-CoA to malonyl-CoA, the committed step in fatty acid synthesis.
Amino Acid Catabolism	Propionyl-CoA Carboxylase	Metabolizes valine, isoleucine, threonine, and odd-chain fatty acids.
Leucine Catabolism	Methylcrotonyl-CoA Carboxylase (MCC)	Metabolizes the amino acid leucine.
Gene Regulation	Biotinylation of Histones	Modulates gene expression and DNA replication [1].

3. Health Benefits with Scientific Evidence

The health benefits of biotin are most clearly established in the context of preventing and treating biotin deficiency. Its role in supplementation for healthy individuals, particularly for cosmetic purposes, is less scientifically supported.

Treatment of Inherited Biotin-Dependent Metabolic Disorders

Biotin is a standard, life-saving treatment for inherited metabolic disorders such as biotinidase deficiency and holocarboxylase synthetase deficiency (collectively known as Multiple Carboxylase Deficiency). These conditions prevent the body from properly utilizing biotin, and high-dose biotin supplementation (typically 5–10 mg/day) is essential to restore carboxylase activity and prevent severe neurological and dermatological complications [3].

Hair, Skin, and Nail Health

Biotin is widely marketed for improving hair and nail quality; however, evidence for this benefit in healthy individuals is limited. Clinical trials and case reports show that biotin supplementation may be effective only in individuals with an underlying biotin deficiency or a disease causing brittle nails or uncombable hair syndrome [2].

“In the vast majority of cases, biotin has no proven efficacy in hair and nail growth of healthy individuals. Only 1 study has shown improvement in nail thickness and firmness, and only in patients with underlying pathology.” [2]

For individuals with acquired or inherited biotin deficiency, supplementation has been shown to resolve symptoms such as alopecia (hair loss) and scaly dermatitis [3].

Metabolic and Neurological Support

Biotin is being investigated for its potential role in other conditions, though the evidence remains preliminary:

• Diabetes: Some small studies suggest that high-dose biotin (e.g., 9 mg/day) may help improve glucose control in people with type 2 diabetes, particularly when combined with chromium, but the data is inconsistent and insufficient to recommend it as a standard treatment [1].
• Multiple Sclerosis (MS): Very high-dose biotin (e.g., 100–300 mg/day) is under investigation for its potential to improve symptoms in progressive MS. The hypothesis is that it may enhance myelin repair and energy production in nerve cells. Preliminary results have been mixed, and this is considered an experimental treatment [1].

4. Dosage and Usage

Recommended Dietary Intake

Because of insufficient data, the Food and Nutrition Board (FNB) established an Adequate Intake (AI) for biotin rather than a Recommended Dietary Allowance (RDA) [1].

Age Group	Adequate Intake (AI)
Adults (19+ years)	30 mcg/day
Pregnancy	30 mcg/day
Lactation	35 mcg/day

Therapeutic and Supplement Dosages

• Supplementation for Hair/Nails: Supplements typically contain high doses, ranging from 1,000 mcg (1 mg) to 10,000 mcg (10 mg) or more.
• Treatment for Metabolic Disorders: Doses for inherited biotin-dependent disorders are significantly higher, often ranging from 5,000 mcg (5 mg) to 10,000 mcg (10 mg) per day [3].
• Experimental Doses (e.g., MS): Doses up to 300 mg (300,000 mcg) per day have been used in clinical trials [1].

Food Sources

Biotin is widely available in many foods. The bioavailability of biotin from food is generally excellent, though raw egg whites contain avidin, a protein that binds tightly to biotin and prevents its absorption. Cooking denatures avidin, eliminating this issue [1]. Excellent food sources include organ meats (especially beef liver), eggs, nuts, seeds, and certain vegetables like sweet potatoes [1].

5. Safety and Precautions

Safety and Side Effects

Biotin is considered very safe. A Tolerable Upper Intake Level (UL) has not been established for biotin because there is no evidence of toxicity from high intakes [1]. Excess biotin is readily excreted in the urine. Side effects are rare, even at high doses, and no adverse effects have been reported in adults consuming up to 20 mg (20,000 mcg) per day [1].

Critical Warning: Interference with Laboratory Tests

The most significant safety concern with biotin supplementation is its potential to interfere with certain clinical laboratory tests [1, 3]. This is a serious warning because it can lead to misdiagnosis and inappropriate medical treatment.

• Mechanism: Biotin is commonly used in laboratory assays (especially those using streptavidin-biotin technology) to measure hormones (e.g., thyroid hormones TSH, T4) and cardiac markers (e.g., troponin) [1]. High levels of biotin from supplements can interfere with these assays, causing falsely high or falsely low results.
• Consequences: Falsely low troponin results can mask a heart attack, and falsely high or low thyroid hormone results can lead to misdiagnosis of thyroid disease [1].
• Precaution: Patients taking high-dose biotin supplements MUST inform their healthcare providers and laboratory personnel before any blood work is performed [3]. Biotin intake should typically be stopped for at least 24–72 hours before testing [3].

Drug Interactions

Certain anticonvulsant medications, including carbamazepine, primidone, phenytoin, and phenobarbital, may lower biotin status by increasing its catabolism or inhibiting its absorption [1].

Contraindications

There are no known absolute contraindications for biotin supplementation, apart from the need to temporarily discontinue use before certain lab tests.

6. References

[1] Office of Dietary Supplements (ODS), National Institutes of Health (NIH). Biotin – Health Professional Fact Sheet. NIH ODS.
URL: https://ods.od.nih.gov/factsheets/Biotin-HealthProfessional/

[2] Patel, D. P., Swink, S. M., & Castelo-Soccio, L. (2017). A Review of the Use of Biotin for Hair Loss. Skin Appendage Disorders, 3(3), 166–169.
URL: https://pmc.ncbi.nlm.nih.gov/articles/PMC5582478/

[3] Bistas, K. G., & Tadi, P. (2023). Biotin. StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing.
URL: https://www.ncbi.nlm.nih.gov/books/NBK554493/