biotin

Biotin (vitamin B7) is a water-soluble B-vitamin that occurs naturally in many foods, including eggs, fish, meat, organ meats (such as liver), seeds, nuts, and certain vegetables (such as sweet potatoes, spinach, and broccoli). The NIH Office of Dietary Supplements describes it as a vitamin that helps the body convert the carbohydrates, fats, and proteins in food into usable energy. It is sold on its own and also as a component of B-complex and multivitamin/mineral supplements.

Biotin is widely marketed for hair, skin, and nail health, but according to the NIH there is "little scientific evidence to support these claims." For brittle nails, the NIH describes the support as a few small studies that did not include a placebo group and did not establish participants' baseline biotin status. For hair and skin, the supporting data are limited to a small number of case reports, only in children and infants who had rare conditions. The NIH indicates that further studies are needed before biotin supplements can be recommended for hair, nail, or skin health, particularly in otherwise healthy people. Most people in the US already obtain adequate biotin from food, and true biotin deficiency is very rare.

There is no Recommended Dietary Allowance (RDA) for biotin; because the available data were judged insufficient to set an RDA, the NIH lists only an Adequate Intake (AI) of about 30 mcg/day for adults (35 mcg/day for those breastfeeding), and most people meet this through diet alone. Many marketed products contain far more (commonly 1,000-10,000 mcg) — amounts well beyond any established requirement and not shown to deliver a proven benefit for hair, skin, or nails. Talk to a doctor, pharmacist, or registered dietitian before taking biotin, especially at high doses, and tell any provider you take it before having blood work done.

The NIH states that biotin has not been shown to cause harm, and no Tolerable Upper Intake Level (UL) has been established because there is no evidence in humans that biotin is toxic even at high intakes. The more clinically important safety issue is not toxicity but laboratory interference: biotin taken above recommended amounts can cause false results on certain blood tests. The FDA has warned about this, and the NIH notes that, according to the FDA, a patient with a high intake of supplemental biotin died after a troponin test (used to help diagnose a heart attack) returned a falsely low result due to biotin interference. This monograph is general information and is not a substitute for personalized medical advice.

The NIH does not describe specific toxic side effects from biotin itself and states it has not been shown to cause harm, even at high intakes. The main practical risk is indirect: high biotin intake can distort certain lab tests, which could contribute to misdiagnosis or inappropriate treatment. If you take biotin supplements, tell your healthcare providers before any blood tests so the results can be interpreted correctly.

Biotin can interact with both medications and laboratory tests. The NIH notes that long-term treatment (at least one year) with antiseizure (anticonvulsant) medications — such as carbamazepine, phenytoin, primidone, or phenobarbital — has been associated with significantly lower biotin levels. Separately, biotin above recommended amounts can interfere with diagnostic assays that use biotin-streptavidin technology, which are commonly used to measure hormones (including thyroid hormone), 25-hydroxyvitamin D, and cardiac markers such as troponin, producing falsely high or falsely low results. Tell your doctor and pharmacist about all supplements and medicines you take.