Biotin (vitamin B7)

Biotin (vitamin B7, sometimes called vitamin H) is a water-soluble B vitamin that works as a coenzyme for several enzymes involved in breaking down and building fats, carbohydrates and amino acids. It is found in many foods (eggs, liver, nuts, seeds, some vegetables) and is also made by gut bacteria, so genuine dietary deficiency is rare. When deficiency does occur — with prolonged raw-egg-white consumption (which binds biotin), certain rare inherited enzyme disorders, long-term tube feeding without biotin, or some anti-seizure medicines — it causes a scaly red rash around the eyes, nose and mouth, hair thinning, and neurological symptoms. Far more clinically important today is not deficiency but interference: biotin is a hugely popular over-the-counter supplement for hair, skin and nails, often taken at very high doses. Because many laboratory immunoassays use a biotin-based detection system, high blood biotin can falsely raise or lower a wide range of unrelated tests — thyroid hormones (mimicking Graves' disease), hormone levels, and, critically, troponin (potentially masking a heart attack). This is why a biotin level, or a careful supplement history, matters when other results look unexpectedly abnormal.

• High-dose biotin supplements — the usual reason; important because it can distort many other immunoassay-based blood tests.
• Assay interference risk — high biotin can falsely alter thyroid tests (mimicking hyperthyroidism), hormone results and troponin (potentially hiding a heart attack); stopping biotin before testing removes this.
• Biotin itself has no known toxicity — the concern is the test interference, not the vitamin.

• Prolonged raw egg white intake — avidin binds biotin.
• Rare inherited enzyme disorders — biotinidase deficiency and related conditions.
• Long-term parenteral/tube feeding without biotin.
• Certain anti-seizure medications — can lower biotin over time.
• Deficiency is otherwise uncommon on a normal diet.