Vitamin H is another name for biotin, also known as vitamin B7. It plays a essential role in converting food into energy by helping enzymes break down fats, carbohydrates, and proteins. Adults need about 30 micrograms (mcg) per day, and most people get enough through a normal diet. The “H” comes from the German words “Haar und Haut,” meaning hair and skin, reflecting its early association with those tissues.
How Biotin Works in Your Body
Biotin doesn’t do much on its own. Instead, it acts as a helper molecule for four critical enzymes that drive some of the most fundamental chemical reactions in your cells. Without biotin attached to them, these enzymes can’t function.
One of these enzymes kicks off the process of building fatty acids, which your body needs for cell membranes, energy storage, and signaling. Another is the first step in gluconeogenesis, the process your liver and kidneys use to produce new glucose when blood sugar drops. This same enzyme also helps produce glutamate, a neurotransmitter your brain relies on for signaling. The remaining two enzymes handle the breakdown of certain amino acids, the building blocks of protein. Together, these four enzymes place biotin at the intersection of fat, sugar, and protein metabolism.
Hair, Skin, and Nail Effects
Biotin’s reputation as a beauty supplement is enormous, but the evidence is more nuanced than marketing suggests. A review in the journal Skin Appendage Disorders examined 18 reported cases of biotin use for hair and nail problems. Every single case showed clinical improvement, but every single patient also had an underlying condition causing poor hair or nail growth, such as an inherited enzyme deficiency, uncombable hair syndrome, or brittle nail syndrome. No randomized controlled trials have demonstrated that biotin supplements improve hair or nails in healthy people with normal biotin levels.
For people who are genuinely deficient, the results can be striking. Children with inherited enzyme deficiencies saw dramatic scalp improvement within six weeks and complete hair regrowth within six months. Three cases of brittle nail syndrome showed improved nail strength and growth on 2,500 to 3,000 mcg per day. An infant with biotin deficiency from a restricted diet regrew hair after two months of supplementation. The pattern is consistent: biotin helps when something is actually wrong with biotin status, not as a general cosmetic booster.
Blood Sugar Regulation
Biotin may influence blood sugar, though the evidence is still developing. A meta-analysis of five randomized controlled trials involving 445 people with type 2 diabetes found that biotin supplementation for 28 to 90 days reduced fasting blood glucose levels. The effect was more pronounced at higher doses. One study in 43 Japanese patients with type 2 diabetes found fasting blood glucose dropped roughly 45% after one month of taking 9 mg of biotin daily (that’s 9,000 mcg, or 300 times the adequate intake). However, biotin supplementation did not significantly change insulin levels across four studies, so the mechanism isn’t fully clear.
Role During Pregnancy
Biotin demand increases during pregnancy. The adequate intake rises to 30 mcg for pregnant women and 35 mcg during breastfeeding. Research published in the Journal of Medical Investigation found that pregnant women carrying smaller-than-expected babies had significantly lower serum biotin levels during their second and third trimesters compared to women with normal-term deliveries. Biotin levels in cord blood also correlated positively with gestational age, suggesting that adequate biotin status supports fetal growth and full-term delivery. Animal studies have shown that maternal biotin deficiency during pregnancy restricts fetal growth.
Signs of Deficiency
Biotin deficiency is uncommon but develops gradually. Early signs are vague: fatigue, thinning hair, and dry, scaly skin rashes. A characteristic pattern called “biotin-deficient face” produces red, flaky patches around the eyes, nose, and mouth. Conjunctivitis (red, irritated eyes) is another common early finding.
If deficiency continues, neurological symptoms emerge. These can include numbness and tingling in the hands and feet, muscle pain, depression, lethargy, and in some cases hallucinations. In severe untreated cases, particularly in infants with an inherited inability to recycle biotin, the consequences include seizures, hearing loss, vision problems, and irreversible developmental delays. People at higher risk include those on prolonged antibiotic therapy, those receiving long-term IV nutrition, heavy alcohol users, and people who regularly eat large quantities of raw egg whites.
Why Raw Egg Whites Are a Problem
Raw egg whites contain a protein called avidin that binds to biotin with extraordinary strength, essentially trapping the vitamin and preventing your body from absorbing it. This binding is tight enough that feeding raw egg whites to animals reliably produces biotin deficiency. Cooking denatures avidin and eliminates the problem, so cooked eggs are actually a fine source of biotin. Egg yolks, meanwhile, are naturally rich in biotin and aren’t affected by avidin.
Daily Needs and Food Sources
The National Institutes of Health sets the adequate intake for biotin at 30 mcg per day for adults. Children’s needs range from 8 mcg (ages 1 to 3) up to 25 mcg (ages 14 to 18). There is no established upper limit for biotin because toxicity from oral intake hasn’t been documented. Your body doesn’t store large reserves of biotin since it’s water-soluble, so consistent dietary intake matters.
Biotin is found in a wide variety of foods. Organ meats (especially liver), egg yolks, nuts, seeds, salmon, dairy products, sweet potatoes, and spinach are all reliable sources. Gut bacteria also produce some biotin, though how much of that your body actually absorbs remains uncertain. Most people eating a varied diet meet their needs without supplements.
Biotin Can Interfere With Lab Tests
One underappreciated risk of high-dose biotin supplements is their ability to skew laboratory results. The FDA has issued warnings that biotin can cause falsely low troponin readings, the test used to diagnose heart attacks. A falsely low result could lead doctors to miss a heart attack in progress. Thyroid function tests and other hormone assays can also be affected. If you take biotin supplements, particularly at doses above the 30 mcg adequate intake, let your healthcare provider know before any blood work. Many biotin supplements marketed for hair and nails contain 5,000 to 10,000 mcg per serving, well into the range that can cause interference.