Biotin is a water-soluble B vitamin, also known as vitamin B7, that helps your body convert food into energy. It acts as a helper molecule for five key enzymes involved in processing fats, carbohydrates, and proteins. Adults need about 30 micrograms per day, and most people get enough through a normal diet.
What Biotin Does in Your Body
Biotin’s main job is to assist a group of enzymes called carboxylases. These enzymes run critical chemical reactions in your metabolism. Without biotin attached to them, they can’t function. Specifically, biotin helps power four major processes: building new fatty acids, producing glucose from non-sugar sources (which keeps your blood sugar stable between meals), breaking down the amino acid leucine, and processing certain fats and proteins into usable energy.
Because biotin is water-soluble, your body doesn’t store large reserves of it. You need a steady supply from food. Any excess is simply excreted in urine, which makes toxicity from food sources essentially a non-issue.
Best Food Sources
Biotin is found in a wide range of foods, but the amounts vary dramatically. Beef liver is the richest common source, with about 31 mcg in a 3-ounce serving, enough to cover a full day’s needs. A single cooked egg provides around 10 mcg. After that, the numbers drop off quickly: canned salmon has 5 mcg per serving, a pork chop or hamburger patty about 3.8 mcg each, and a quarter cup of roasted sunflower seeds provides 2.6 mcg.
Plant sources tend to offer smaller amounts. Half a cup of cooked sweet potato gives you 2.4 mcg, while a quarter cup of roasted almonds has 1.5 mcg. Spinach, broccoli, oatmeal, and bananas all contain trace amounts under 1 mcg per serving. Fruits like apples and grains like whole wheat bread contain essentially none.
One dietary quirk worth knowing: raw egg whites contain a protein called avidin that binds tightly to biotin and blocks your body from absorbing it. Cooking eggs deactivates avidin, so this is only a concern if you regularly consume raw egg whites, as some athletes do in shakes or smoothies.
How Much You Need
The recommended adequate intake for adults is 30 mcg per day. Pregnant women need the same amount, and breastfeeding women need slightly more at 35 mcg. Children need less, ranging from 5 mcg for infants up to 25 mcg for teenagers. Because biotin is spread across so many common foods, most people in developed countries meet these targets without thinking about it.
Signs of Deficiency
Biotin deficiency is rare in healthy adults, but when it does occur, the symptoms tend to develop gradually and can be easy to miss at first. Early signs include fatigue, thinning hair, and dry, scaly skin rashes. A characteristic pattern called “biotin-deficient face” can develop, with red, flaky skin concentrated around the eyes, nose, and mouth. These skin problems stem from impaired fatty acid metabolism, since biotin-dependent enzymes are needed to build the fats that keep skin healthy.
If the deficiency progresses, neurological symptoms can appear: tingling or numbness in the hands and feet, muscle pain, depression, and lethargy. In severe, untreated cases, more serious complications like seizures, hearing loss, and cognitive impairment have been documented. Children with deficiency may experience developmental delays. Nausea, vomiting, and loss of appetite are also possible.
The people most at risk include those with genetic disorders affecting biotin metabolism, heavy alcohol users, people on long-term anti-seizure medications, and anyone consuming large quantities of raw egg whites. Pregnancy can also lower biotin levels, as the growing fetus increases demand.
Biotin for Hair, Skin, and Nails
Biotin supplements are heavily marketed for hair growth and stronger nails, and they’re one of the most popular beauty supplements on the market. The reality is more nuanced. In people who are actually biotin-deficient, supplementation does reverse hair loss and skin problems, because those symptoms were caused by the deficiency in the first place. But for people with normal biotin levels, the evidence is thin.
A review published in Skin Appendage Disorders found no randomized controlled trials demonstrating that biotin supplements benefit hair or nail growth in healthy individuals. Lab studies have also shown that biotin doesn’t influence the growth or development of normal hair follicle cells. The authors concluded there is no evidence to support biotin supplementation outside of confirmed deficiency. Despite this, many supplements contain 5,000 to 10,000 mcg of biotin per dose, well over 100 times the daily adequate intake.
Biotin Can Interfere With Lab Tests
This is the part most people don’t know about, and it matters. The FDA has warned that high-dose biotin supplements can significantly skew the results of certain laboratory tests. The interference affects tests that use a common detection method called immunoassay, which includes blood work for thyroid function, hormone levels, and cardiac markers like troponin (used to diagnose heart attacks).
The danger is real: a falsely low troponin reading could cause a doctor to miss a heart attack, while a falsely abnormal thyroid result could lead to unnecessary treatment. The interference can go undetected because the test simply returns an inaccurate number with no error flag. If you take biotin supplements, especially at doses above the standard 30 mcg, let your doctor and the lab know before any blood work. Most experts recommend stopping high-dose biotin supplements at least 72 hours before testing.