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Vitamin B7 (Biotin) — The Complete Supplement Guide

The "hair, skin and nails" vitamin — with weaker evidence than the marketing suggests, and a real habit of skewing blood tests. Function, doses and the lab-test warning.

Reviewed by Bodil Isaksson, Licensed Biomedical Scientist (Sweden)Last reviewed July 2026Supplement guide

SupplementsVitaminsB7 BiotinWater-soluble

Hugely popular for hair and nails — but its most important practical point is that high-dose biotin can distort common blood tests, from thyroid to troponin. For the short dietary version, see the Vitamins page.

Read first — blood tests. High-dose biotin can falsify lab results (thyroid hormones, troponin and others), risking missed or wrong diagnoses. Always tell your doctor if you take it, and stop before blood tests. Information, not a prescription.

Key takeaways

  • High “beauty” doses (5,000–10,000 µg) can distort blood tests — tell your doctor if you take it.
  • Adults: about 30–40 µg/day (adequate intake).
  • No upper limit set, but lab-test interference is the real concern.

Function

Biotin is a coenzyme for the "carboxylase" enzymes:

  • Metabolism: a cofactor for enzymes handling fat, carbohydrate and protein metabolism.
  • Fatty-acid synthesis and the breakdown of certain amino acids.
  • Gluconeogenesis: helps the body make glucose when needed.
  • Gene regulation: involved in modifying histones that switch genes on and off.

Different forms — and which to choose

D-biotinThe standard (and only meaningful) supplement form, often in very high "beauty" doses.
In multivitaminsPresent at small, sensible doses that don't interfere with tests.

Absorption in the body

How muchWell absorbed; gut bacteria also make some. Raw egg white contains avidin, which binds biotin and blocks it (cooking destroys avidin).

Deficiency symptoms

SymptomsRare — thinning hair, a scaly red rash around the eyes/nose/mouth, and brittle nails.
Who's at riskRegular raw-egg-white consumption, long-term tube feeding, some genetic disorders, and pregnancy (needs rise slightly).

Recommended intake

Adults AI ≈ 30–40 µg/day

An adequate-intake figure:

  • Adults: ~30–40 µg/day

Best sources: egg yolk, nuts, seeds, salmon, sweet potato and organ meats.12

Therapeutic use

Hair & nailsWidely sold for these, but the evidence is weak unless you are genuinely deficient; brittle-nail data are limited.
DeficiencyCorrecting true deficiency clearly helps skin, hair and metabolism.

Therapeutic doses

Beauty doses often 5,000–10,000 µg
RealityMarketed mega-doses far exceed needs; benefit for non-deficient people is unproven.
Before blood testsStop high-dose biotin several days before testing and tell your doctor.

Toxicity & upper limit

No UL — but interferes with lab tests
Upper limitNo formal UL; biotin itself is not toxic.1
Test interferenceThe key hazard: high-dose biotin can falsify thyroid, troponin and hormone assays — a documented cause of misdiagnosis.

Bottom line: biotin from eggs, nuts and fish covers needs, and high-dose "hair and nail" supplements rarely help unless you're deficient. If you do take them, stop before any blood test and tell your doctor — the test interference is the real risk.

← All supplementsShort dietary version

References

Reference and upper-limit values are general adult figures from official bodies; individual needs vary. Therapeutic doses describe clinical/research use, not prescriptions.

  1. US NIH Office of Dietary Supplements. Biotin — Health Professional Fact Sheet (function, forms, intakes, food sources, deficiency, therapeutic uses, upper limit, interactions). ods.od.nih.gov
  2. EFSA. Dietary Reference Values & Tolerable Upper Intake Levels for vitamins (European reference intakes and ULs). efsa.europa.eu

This article summarizes nutrition science from official health authorities and peer-reviewed sources for education. It is not a substitute for individual medical advice, and the doses given are not prescriptions — always consult a professional before therapeutic supplement use, in pregnancy, or alongside medication.

✓
Bodil Isaksson, Licensed Biomedical Scientist (Sweden)

At Food Health Lab we explain what the science says in plain language, and we cite our sources so you can check for yourself.

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