Biotin
Biotin (Vitamin B7)
Biotin (Vitamin B7) is a water-soluble B-vitamin that serves as an essential cofactor for carboxylase enzymes involved in fatty acid synthesis, gluconeogenesis, and amino acid metabolism. It is widely used to support hair, skin, and nail health, and is also used therapeutically in high doses for certain metabolic disorders such as biotinidase deficiency and multiple carboxylase deficiency. Supplementation is popular among consumers seeking to improve hair thickness and nail strength, though evidence in non-deficient individuals is limited.
Mechanism of Action
Biotin functions as a covalently bound coenzyme for five mammalian carboxylases, including acetyl-CoA carboxylase, pyruvate carboxylase, and propionyl-CoA carboxylase, enabling critical carboxylation reactions in lipid synthesis, gluconeogenesis, and branched-chain amino acid catabolism. It is transported into cells via the sodium-dependent multivitamin transporter (SMVT) and biotinylates histones in the nucleus, playing a role in chromatin remodeling and gene expression. Deficiency impairs these enzymatic functions, leading to dermatitis, alopecia, and neurological symptoms that resolve with supplementation.
Evidence by Health Goal(15 goals)
Dosing Protocols
With or without food
Adequate Intake (AI) is 30mcg/day for adults. This dose is sufficient to prevent deficiency in healthy individuals. Most standard multivitamins contain this range.
With or without food
High-dose range commonly marketed for hair, skin, and nail benefits. Evidence in non-deficient individuals is weak. Doses above 5,000mcg can significantly interfere with immunoassay-based laboratory tests (troponin, thyroid hormones, hormone panels). Discontinue at least 72 hours before blood draws.
Safety & Side Effects
Biotin has an excellent safety profile at physiological and even high supplemental doses, as excess is renally excreted and no tolerable upper intake level has been established due to lack of toxicity data. The most clinically significant concern is interference with immunoassay laboratory diagnostics at doses commonly found in over-the-counter supplements (≥5,000mcg), which has been linked to misdiagnosis events reported to the FDA.
Possible Side Effects
- !Laboratory test interference — falsely elevated or depressed results on immunoassay-based tests (thyroid, troponin, hormone panels) at doses ≥5,000mcg
- !Mild acne or skin breakouts reported anecdotally at high doses
- !Gastrointestinal discomfort (bloating, nausea) at doses above 10,000mcg
- !Allergic skin rash in rare cases of hypersensitivity
- !Possible falsely low troponin readings masking cardiac events at very high supplemental doses
Interactions
- -Interferes with biotin-streptavidin immunoassay laboratory tests — can cause falsely high or low results for TSH, free T4, T3, estradiol, progesterone, testosterone, and troponin at doses ≥5,000mcg
- -Anticonvulsants (valproic acid, phenobarbital, carbamazepine, phenytoin) — long-term use may impair biotin absorption and accelerate its catabolism, potentially inducing functional deficiency
- -Raw egg whites — contain avidin, which binds biotin in the gut and prevents absorption; chronic raw egg white consumption can deplete biotin
- -Alpha-lipoic acid — may compete with biotin for SMVT-mediated intestinal absorption when taken together in high doses
- -Antibiotics (broad-spectrum) — may reduce gut bacterial synthesis of biotin, marginally decreasing endogenous contribution
Cost & Where to Buy
Biotin is widely available and inexpensive. Standard doses (30-300mcg) cost as little as $3/month as part of a B-complex or multivitamin. High-dose standalone supplements (5,000-10,000mcg) range from $6-$20/month depending on brand and form.
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