Biotin, also called vitamin B7, is a water-soluble vitamin that helps your body convert food into energy. It acts as a helper molecule for four essential enzymes involved in processing fats, carbohydrates, and proteins. Most people get enough biotin from a normal diet, but the vitamin has gained outsized attention for its supposed benefits to hair, skin, and nails. Here’s what it actually does, what the evidence supports, and what you should know before supplementing.
How Biotin Powers Your Metabolism
Biotin’s core job is activating four carboxylase enzymes, each responsible for a different metabolic process. Pyruvate carboxylase helps your body produce glucose when blood sugar runs low. Acetyl-CoA carboxylase kicks off fatty acid synthesis, the process your body uses to build and store fat. Propionyl-CoA carboxylase breaks down odd-chain fatty acids. And beta-methylcrotonyl-CoA carboxylase handles the breakdown of the amino acid leucine, which is abundant in muscle tissue.
Without biotin, none of these enzymes can function. That means your body would struggle to regulate blood sugar, build cell membranes, and process the protein you eat. This is why severe biotin deficiency, though rare, causes such wide-ranging symptoms: fatigue, muscle pain, tingling in the hands and feet, and skin rashes.
The Hair, Skin, and Nail Claims
Biotin supplements are marketed heavily for thicker hair, clearer skin, and stronger nails. The reality is less impressive. A review published in the Journal of the American Academy of Dermatology found that biotin has not been shown to benefit healthy hair or improve hair conditions in people who aren’t biotin-deficient. The majority of published evidence consists of individual case reports, not controlled trials, and there remains a clear lack of randomized studies supporting routine biotin use for cosmetic purposes.
The case reports that do show dramatic results almost always involve people with confirmed biotin deficiency or a genetic inability to process the vitamin. In those cases, supplementation can be striking: one child with a metabolic disorder and total hair loss regrew a full head of hair within a month on biotin. Adults on intravenous nutrition who lost their hair saw regrowth within two months of adding biotin. But these are people whose bodies were starved of the vitamin entirely.
For someone eating a normal diet, taking extra biotin is unlikely to change anything about your hair or nails. Biotin is water-soluble, so excess amounts are simply excreted in urine. Your body doesn’t stockpile it, and flooding your system with more than it needs doesn’t amplify the vitamin’s effects.
Biotin’s Role in Gene Regulation
Beyond metabolism, biotin plays a subtler role inside your cells. It attaches to proteins called histones, which act like spools that DNA wraps around. When biotin binds to a specific site on histone H4, the DNA wraps more tightly, about 13% more tightly in lab measurements. This added compression effectively silences certain genes, preventing them from being read and translated into proteins.
This process is part of how your cells control which genes are active at any given time. It’s not something you’d notice day to day, but it matters for normal cell function and development.
Why Biotin Matters During Pregnancy
Up to 50% of pregnant women in the United States develop a marginal biotin deficiency, particularly in the early weeks of pregnancy. This is concerning because biotin, alongside folic acid, appears to play a role in preventing birth defects. A retrospective review of U.S. pregnancies found that women who did not take prenatal vitamins were twice as likely to have infants with a major birth defect compared to those who took standard prenatal vitamins containing biotin and folic acid.
The exact mechanism is still being studied, but biotin’s role in gene regulation and its involvement in building fatty acids (which are critical for developing cell membranes) likely contribute to its importance during fetal development. Most prenatal vitamins already include biotin, so this isn’t typically something that requires a separate supplement.
How Much You Need and Where to Find It
Adults need 30 micrograms (mcg) of biotin per day. Pregnant women need the same amount, while breastfeeding women need 35 mcg. Children’s needs range from 5 mcg for infants up to 25 mcg for teenagers.
Biotin is found in a wide range of common foods. Beef liver is one of the richest sources. Eggs are another good source, but only when cooked, because raw egg whites contain a protein called avidin that binds to biotin and blocks absorption. Salmon, sunflower seeds, sweet potatoes, and almonds all contribute meaningful amounts. Gut bacteria also produce some biotin on their own, though how much the body actually absorbs this way isn’t fully clear.
Because biotin is so widely available in food, true deficiency is uncommon. It’s most often seen in people on long-term intravenous feeding, those taking certain anti-seizure medications, people with genetic disorders affecting biotin metabolism, and heavy alcohol users.
Biotin Can Interfere With Lab Tests
This is the most practically important thing to know if you take biotin supplements. The FDA has warned that biotin can significantly interfere with certain laboratory tests, producing incorrect results that may go undetected. The interference is especially dangerous with troponin tests, which measure a protein released during heart attacks. Biotin can cause falsely low troponin readings, potentially masking a cardiac emergency.
Thyroid function tests are also affected. Depending on the test design, biotin can make thyroid hormone levels appear falsely high or falsely low, leading to misdiagnosis. The problem isn’t limited to people taking megadoses. Many hair, skin, and nail supplements contain 5,000 to 10,000 mcg of biotin per serving, which is more than 150 times the daily adequate intake.
If you take biotin supplements and need blood work, let your doctor know beforehand. Stopping biotin for at least 48 to 72 hours before testing is generally recommended to avoid skewed results. This is especially critical if you’re being evaluated for heart symptoms or thyroid problems.