Biotin has earned a reputation as the “beauty vitamin” for its supposed ability to strengthen hair, skin, and nails. Walk through any pharmacy and you’ll find shelves of biotin supplements promising thicker hair and stronger nails. But does the science actually support these claims?

I’ve gone through the clinical research to separate fact from marketing hype. The picture that emerges is more nuanced than supplement labels would have you believe.

What is biotin?

Biotin, also known as vitamin B7, belongs to the vitamin B complex family. The name derives from the German words for hair (Haar) and skin (Haut), which tells you something about its traditional associations.

At the biochemical level, biotin acts as a coenzyme for five carboxylases in the human body. These enzymes are involved in fatty acid synthesis, gluconeogenesis (making glucose from non-carbohydrate sources), and amino acid metabolism. Without biotin, your body cannot properly produce energy from the food you eat [1].

Beyond metabolism, biotin plays a role in immune function. It participates in antibody production, lymphocyte differentiation, and the normal functioning of macrophages and natural killer cells. There’s also growing evidence that biotin influences gene expression, with approximately 2,000 biotin-dependent genes identified so far that affect transcriptional regulation and genomic stability [2].

Is biotin deficiency common?

Not really. Biotin deficiency is actually quite rare in people who eat a varied diet. The vitamin appears in so many foods that most people get adequate amounts without trying.

When deficiency does occur, symptoms can include:

Thinning hair and hair loss across the body
Brittle nails that crack or peel
Dry, irritated eyes
Skin rashes, particularly around the eyes, nose, and mouth
Seborrhoeic dermatitis
Nausea, vomiting, and loss of appetite
Neurological symptoms including depression, lethargy, numbness and tingling in extremities
In severe cases: seizures and developmental delays in children

The NHS notes that biotin deficiency is “very rare” in the UK, partly because gut bacteria can actually synthesise small amounts of the vitamin [3].

What causes biotin deficiency?

While uncommon, several factors can lead to deficiency:

Congenital causes: Biotinidase deficiency is an inherited disorder that prevents the body from recycling biotin properly. This autosomal recessive condition can cause severe deficiency with neurological and skin symptoms if untreated.

Raw eggs: Here’s something your grandmother might have warned you about. Raw egg whites contain a protein called avidin that binds tightly to biotin, preventing absorption. Cooking denatures avidin, which is why cooked eggs don’t cause this problem. Eating large quantities of raw eggs (something bodybuilders sometimes do) can genuinely lead to deficiency.

Medications: Certain drugs interfere with biotin:

Antiepileptic medications (valproic acid, carbamazepine, phenobarbital, phenytoin, primidone)
Long-term antibiotics, which can destroy biotin-producing gut bacteria

Digestive conditions: Crohn’s disease and other inflammatory bowel conditions can impair biotin absorption.

Alcohol: Chronic heavy drinking inhibits biotin absorption.

Parenteral nutrition: Patients receiving long-term intravenous feeding may not get adequate biotin.

Food sources of biotin

Biotin is widespread in the food supply. Good sources include:

Egg yolks (cooked)
Organ meats (liver, kidney)
Nuts, particularly almonds, peanuts, and walnuts
Legumes and soybeans
Whole grains
Mushrooms
Bananas
Cauliflower
Fish and seafood
Dairy products

Heavy processing can destroy biotin, so minimally processed foods generally provide more than their processed counterparts.

The evidence for biotin’s benefits

1. Hair loss: probably only helpful if you’re deficient

This is the big one that everyone asks about. Biotin supplements have become hugely popular for hair loss, but the evidence is far more limited than marketing would suggest.

A systematic review examining 18 case reports of biotin use for hair and nail problems found something important: supplementation only helped in cases where there was an underlying biotin deficiency, either from inherited conditions or acquired causes. The review found “no evidence” that biotin improved hair growth in healthy individuals without deficiency [4].

This makes sense when you think about it. If your body already has enough biotin, adding more doesn’t give your hair follicles extra building material to work with.

My honest assessment: unless you have a documented biotin deficiency (which is rare), biotin supplements probably won’t do much for your hair. The people in those before-and-after photos on supplement websites? They likely had underlying deficiencies that supplementation corrected.

2. Multiple sclerosis: high-dose treatment shows some promise

Multiple sclerosis (MS) is a debilitating neurological condition where the immune system attacks the myelin sheath protecting nerve fibres. Progressive forms of MS currently have limited treatment options.

Researchers have been investigating whether high-dose biotin (much higher than typical supplements) might help repair myelin or enhance nerve energy production.

A meta-analysis of three randomised controlled trials involving 889 MS patients found that high-dose biotin (300 mg daily, far exceeding the typical 30-100 mcg supplements) for 12-15 months was associated with improved walking speed as measured by the timed 25-foot walk test [5].

The proposed mechanism involves biotin’s role in activating certain enzymes that could enhance myelin repair and boost production of ATP, the cellular energy currency that nerves depend on.

However, I should be clear: this is still considered experimental. The sample sizes were modest, and high-dose biotin treatment for MS is not yet standard practice. Trials continue.

3. Amyotrophic lateral sclerosis (ALS): too early to tell

ALS (Lou Gehrig’s disease) is a devastating condition where motor neurons progressively degenerate, leading to muscle weakness, paralysis, and eventually respiratory failure.

A small randomised, double-blind trial gave 30 ALS patients either high-dose biotin (300 mg daily) or placebo for 24 weeks. The treatment was well tolerated, and researchers observed a slightly slower decline in respiratory function in the biotin group [6].

But 30 patients is a tiny sample size, and the clinical characteristics varied considerably between participants. This is hypothesis-generating research, not evidence that biotin helps ALS. Much larger trials would be needed.

4. Brittle nails: limited but encouraging evidence

Brittle nail syndrome affects roughly 20% of the population, with women affected twice as often as men. Nails become weak, peel, crack, and break easily. The cause is usually unknown, though it can stem from skin conditions, nutritional deficiencies, medication effects, or trauma.

Interestingly, veterinarians have long used biotin to treat hoof problems in horses, cattle, and sheep [7].

Several small human studies have found improvements with biotin supplementation. In combined data, 63-91% of subjects with brittle nails reported improvement, and nail plate thickness increased measurably [8,9].

The mechanism likely involves biotin’s role in synthesising lipid molecules needed for keratinocyte development in the nail plate.

The evidence here is genuinely encouraging, though I’d note the studies were small and often lacked rigorous controls. Still, for something as low-risk as biotin for brittle nails, it seems reasonable to try.

5. Blood sugar control in diabetes: may help as part of combination therapy

Diabetes affects hundreds of millions of people worldwide, making any potential adjunct therapy worth investigating.

Some research has found that people with diabetes tend to have lower blood biotin concentrations than healthy individuals, and that supplementation might improve fasting blood glucose [10].

More compelling is a 90-day double-blind trial in 447 diabetic patients with poor blood sugar control. Adding chromium and biotin to standard treatment improved glycated haemoglobin (HbA1c) and fasting blood glucose compared to medication alone [11].

The mechanism may involve biotin’s effects on glucokinase (an enzyme involved in hepatic glucose metabolism) and its influence on insulin signalling [12].

The catch? Most positive studies used biotin combined with chromium, making it difficult to separate the individual effects. Biotin alone may not be as effective.

Side effects of biotin

Biotin has an excellent safety profile. Because it’s water-soluble, excess amounts are excreted in urine rather than building up in tissues. Studies have used doses up to 600 mg daily for several months without significant adverse effects.

That said, comprehensive long-term safety data at very high doses are lacking. If you’re considering high-dose biotin, discuss it with your doctor first.

Safety precautions (4 contraindications)

1. Laboratory test interference: this one is genuinely important

Biotin can significantly interfere with certain blood tests that use biotin-streptavidin immunoassay technology. This isn’t a theoretical concern; it can cause clinically significant false results.

Affected tests may include:

Thyroid function (free T4, free T3, TSH, thyroid receptor antibodies)
Hormone levels (testosterone, oestradiol)
Vitamin levels (folic acid, B12, vitamin D)
Cardiac markers (troponin)
Tumour markers

High-dose biotin users have received incorrect diagnoses of hyperthyroidism based on falsely abnormal thyroid tests. The Mayo Clinic and FDA have both issued warnings about this [13].

If you take biotin supplements, always inform your doctor before blood tests. Consider stopping biotin 3-7 days before testing to allow clearance.

2. Interaction with pantothenic acid (vitamin B5)

High doses of pantothenic acid may compete with biotin for absorption. If you’re taking both, space them apart or choose a balanced B-complex that accounts for this.

3. Antibiotics and antimicrobials

Antibiotics, particularly broad-spectrum ones, can destroy the gut bacteria that synthesise biotin. Long-term antibiotic use might reduce your biotin status.

4. Antiepileptic medications

Drugs including carbamazepine, phenobarbital, phenytoin, and primidone reduce both intestinal absorption of biotin and its reabsorption in the kidneys [14]. People on long-term anticonvulsant therapy may need to monitor biotin status and potentially supplement.

Dosage

There’s no established recommended dietary allowance (RDA) for biotin in most countries, only “adequate intake” levels. For adults, this is typically 30-35 mcg daily, an amount easily obtained from food.

Supplements typically contain 1,000-10,000 mcg (1-10 mg), far exceeding the adequate intake. For conditions like brittle nails, studies have generally used 2,500-5,000 mcg daily.

For neurological conditions like MS, the experimental doses (300 mg daily) are in an entirely different range and should only be used under medical supervision.

The bottom line

Biotin is a genuine essential nutrient with real functions in the body. However, the evidence for supplementation in healthy people is weak. Most benefits appear limited to those with documented deficiency.

For specific conditions like brittle nails, biotin supplements may help even without overt deficiency, though the evidence is modest. For blood sugar management, combination therapy with chromium shows more promise than biotin alone.

Perhaps most importantly: be aware of the laboratory test interference issue. This is a practical concern that can lead to misdiagnosis if you don’t inform your healthcare providers about biotin use.

References

Zempleni J, Wijeratne SS, Hassan YI. Biotin. Biofactors. 2009;35(1):36-46. https://pubmed.ncbi.nlm.nih.gov/19319844/
Zempleni J, Teixeira DC, Kuroishi T, et al. Biotin requirements for DNA damage prevention. Mutat Res. 2012;733(1-2):58-60. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4757853/
NHS. B vitamins and folic acid. https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-b/
Patel DP, Swink SM, Castelo-Soccio L. A Review of the Use of Biotin for Hair Loss. Skin Appendage Disord. 2017;3(3):166-169. https://pubmed.ncbi.nlm.nih.gov/28879195/
Luo J, Li Y, Zhang J, et al. High-dose biotin for progressive multiple sclerosis: A systematic review and meta-analysis. Mult Scler Relat Disord. 2021;55:103184. https://pubmed.ncbi.nlm.nih.gov/34332461/
Ramirez-Alfaro A, Nwosu G, Moya L, et al. High-dose biotin in amyotrophic lateral sclerosis: A randomized controlled trial. Muscle Nerve. 2020;61(3):391-397. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7046518/
Josseck H, Zenker W, Geyer H. Hoof horn abnormalities in Lipizzaner horses and the effect of dietary biotin on macroscopic aspects of hoof horn quality. Equine Vet J. 1995;27(3):175-182. https://www.ncbi.nlm.nih.gov/pubmed/8202678
Hochman LG, Scher RK, Meyerson MS. Brittle nails: response to daily biotin supplementation. Cutis. 1993;51(4):303-305. https://www.ncbi.nlm.nih.gov/pubmed/8477615
Floersheim GL. Treatment of brittle fingernails with biotin. Z Hautkr. 1989;64(1):41-48. https://www.ncbi.nlm.nih.gov/pubmed/2648686
Maebashi M, Makino Y, Furukawa Y, et al. Therapeutic evaluation of the effect of biotin on hyperglycemia in patients with non-insulin dependent diabetes mellitus. J Clin Biochem Nutr. 1993;14(3):211-218. https://www.jstage.jst.go.jp/article/jcbn1986/14/3/14_3_211/_article
Singer GM, Geohas J. The effect of chromium picolinate and biotin supplementation on glycemic control in poorly controlled patients with type 2 diabetes mellitus. Diabetes Technol Ther. 2006;8(6):636-643. https://www.ncbi.nlm.nih.gov/pubmed/17506119
Fernandez-Mejia C. Pharmacological effects of biotin. J Nutr Biochem. 2005;16(7):424-427. https://www.ncbi.nlm.nih.gov/pubmed/22841397
Trambas C, Loh T, Engel M, et al. Biotin Interference in Routine Clinical Immunoassays: Understand the Causes and Mitigate the Risks. Ann Clin Biochem. 2020;57(4):291-305. https://pubmed.ncbi.nlm.nih.gov/32445355/
Mock DM, Dyken ME. Biotin catabolism is accelerated in adults receiving long-term therapy with anticonvulsants. Neurology. 1997;49(5):1444-1447. https://pubmed.ncbi.nlm.nih.gov/9371938/