Vitamin B7, commonly known as biotin, is a water-soluble B vitamin that helps your body convert food into energy. Adults need about 30 micrograms (mcg) per day, and most people get enough through a normal diet. Despite its massive popularity as a hair and nail supplement, the clinical evidence behind those claims is surprisingly thin.
What Biotin Does in Your Body
Biotin works as a helper molecule for four key enzymes in human metabolism. Each one drives a different process: one supports the creation of new glucose (your body’s primary fuel), another handles the breakdown of certain fatty acids, a third is involved in building new fatty acids, and the fourth helps break down amino acids from protein. Without biotin, none of these enzymes can function properly.
In practical terms, this means biotin plays a role in how your body processes nearly every type of food you eat: carbohydrates, fats, and proteins. It’s a behind-the-scenes nutrient, not one you’d notice when levels are normal, but one that causes widespread problems when levels drop too low.
Best Food Sources
Biotin is found in a wide range of foods, so outright deficiency from diet alone is uncommon. Some of the richest sources include eggs (cooked), liver, salmon, pork, beef, sunflower seeds, sweet potatoes, and almonds. Dairy products, whole grains, and many vegetables also contribute smaller amounts. Gut bacteria produce some biotin as well, though how much of that your body actually absorbs remains unclear.
One food-related quirk worth knowing: raw egg whites contain a protein called avidin that binds to biotin with extraordinary strength, forming what’s considered the strongest non-covalent bond in nature. This bond survives digestion, preventing your body from absorbing the biotin. Cooking eggs to at least 100°C (212°F) denatures avidin and releases biotin for normal absorption. A whole raw egg isn’t as problematic as pure raw egg white, because the yolk’s biotin content roughly offsets the avidin in the white. But eating large amounts of raw egg whites over weeks or months can genuinely deplete your biotin levels.
How Much You Need
Biotin doesn’t have a formal Recommended Dietary Allowance (RDA) because there isn’t enough data to set one precisely. Instead, the NIH provides an Adequate Intake (AI) level, which is an estimate based on the amounts healthy people typically consume.
- Infants (0 to 12 months): 5 to 6 mcg
- Children (1 to 8 years): 8 to 12 mcg
- Children (9 to 13 years): 20 mcg
- Teens (14 to 18 years): 25 mcg
- Adults (19+): 30 mcg
- Pregnant women: 30 mcg
- Breastfeeding women: 35 mcg
No Tolerable Upper Intake Level (UL) has been established for biotin, which is sometimes misinterpreted to mean high doses are perfectly safe. In reality, it just means there hasn’t been enough research to define a ceiling. As discussed below, high-dose supplements carry a real and well-documented risk of skewing lab test results.
Signs of Deficiency
True biotin deficiency is rare in the general population, but when it occurs, the symptoms are distinctive. The most recognizable physical signs are hair loss and a scaly red rash that typically appears around the eyes, nose, mouth, and genital area. Neurological symptoms can also develop, including depression, lethargy, numbness and tingling in the hands and feet, difficulty with coordination, and in severe cases, hallucinations or seizures.
Certain groups face a higher risk. People receiving long-term intravenous nutrition without biotin added to the solution are vulnerable, as are infants fed formulas that lack biotin. Long-term use of anti-seizure medications can interfere with biotin absorption and increase how quickly the body breaks it down. Smoking accelerates biotin breakdown as well. Pregnant women are another at-risk group: research suggests a substantial number develop marginal biotin deficiency during normal pregnancy, even without obvious symptoms. Certain liver diseases can reduce the body’s ability to recycle biotin, and rare inherited conditions like biotinidase deficiency impair biotin absorption from birth.
Biotin for Hair and Nails
Biotin supplements are marketed aggressively for hair growth and nail strength, and they’re among the most popular beauty supplements on the market. The actual evidence, however, tells a different story. A 2024 review in the Journal of the American Academy of Dermatology described the clinical support as “limited,” noting it consists mostly of isolated case reports rather than controlled trials. The authors wrote that “societal infatuation with biotin supplementation” is “vastly disproportionate to the insufficient clinical evidence supporting its efficacy.”
There are narrow exceptions. People with confirmed biotinidase deficiency clearly benefit from high-dose biotin, and there are anecdotal reports of improvement in conditions like brittle nail syndrome and uncombable hair syndrome. But for healthy individuals who already get enough biotin through diet, there is little reason to expect that extra biotin will make hair grow faster or nails grow stronger. If you’re experiencing hair loss or brittle nails, it’s more useful to investigate the underlying cause than to add a supplement.
The Lab Test Problem
This is the most important safety issue with biotin supplements, and it’s one many people don’t know about. High-dose biotin can interfere with a wide range of common lab tests, producing results that are either falsely high or falsely low. The FDA has issued safety warnings about this, specifically highlighting interference with troponin tests. Troponin is the primary blood marker used to diagnose heart attacks, and falsely low readings caused by biotin interference could lead to a missed diagnosis.
Thyroid function tests are also affected. Biotin can cause results that mimic hyperthyroidism (overactive thyroid) in a person with a perfectly normal thyroid, potentially triggering unnecessary treatment. The interference extends to hormone panels, vitamin D tests, and other immunoassays that use biotin-based chemistry in their design.
Many over-the-counter biotin supplements contain 5,000 to 10,000 mcg per pill, which is 166 to 333 times the daily adequate intake. At these doses, the risk of lab interference is real. If you take biotin supplements and need blood work, let your healthcare provider know. Stopping the supplement for a few days before testing is typically enough to clear biotin from your system and restore accurate results.
Why Excess Biotin Isn’t Simply Harmless
Because biotin is water-soluble, your kidneys do filter out excess amounts. This has led to a general perception that you can’t really take too much. While biotin at high doses doesn’t appear to cause direct toxicity in the way that fat-soluble vitamins like A or D can, the lab test interference described above is a concrete, documented harm. The Journal of the American Academy of Dermatology review put it plainly: there is “scant evidence for supplementation in healthy individuals, but definite risk of potential harm.” For most people eating a varied diet, the 30 mcg your body needs is already covered by food.