Biotin deficiency and thyroid tests


What is biotin?

Biotin is a water-soluble (cannot be stored by the body) B vitamin (B7). The body needs biotin to process glucose and to metabolize proteins, fats, and carbohydrates.1 It also helps to transfer carbon dioxide.2

The body cannot make its own biotin. It is found in many foods such as meat, fish, eggs, and organ meats, seeds and nuts and sweet potatoes, spinach, and broccoli.1

Biotin also comes from the bacteria in your gut. Dietary protein-bound biotin is converted to free biotin before being absorbed in the small and large intestine.3

Biotin is essential for foetal development so ensure that you are not deficient during pregnancy.1

What are the symptoms of biotin deficiency?

Biotin deficiency is very rare. It can cause thinning hair and loss of body hair; a rash around the eyes, nose, mouth, and anal area; pinkeye; high levels of acid in the blood and urine; seizures; skin infection; brittle nails; depression; lethargy and pins and needles in the extremities.1

Symptoms of biotin deficiency in infants include weak muscle tone, sluggishness, and delayed development.4

Long term anti-seizure medication may cause a biotin deficiency as can eating egg whites over a long term.1

Biotin is promoted to be good for hair, skin and nail health. Some studies have shown that taking biotin improved brittle nails.  However, although it is known that biotin deficiency causes hair loss, there are no studies showing that taking biotin supplements improves hair loss.1

There are a few studies now that show that biotin is helpful for patients with MS.1

There is no recommended daily dose of biotin.  However, the Department of Health state that taking 0.9mg or less a day of biotin in supplements is unlikely to cause any harm.5  Biotin can come as part of a B complex supplement or on its own. It’s best to see a nutritionist, though, and you can then discuss any supplementation needed.

Effect of biotin on test results

Biotin has not been shown to be toxic. However, supplements that contain biotin above recommended amounts may cause false results in some lab tests, including those that measure levels of certain hormones, like thyroid hormone.6, 7

There is a case where a woman taking high doses of biotin for hair loss became thyrotoxic according to her test results – her FT4 levels rose to a very high level.8 Of course, it could be that the biotin aided gut health which then meant she didn’t need so much levothyroxine.

If you take biotin and your FT4 levels rise, your GP may be concerned and possibly reduce your dosage so be aware of this.

If you suspect you may be deficient, ensure you eat plenty of biotin-rich foods as a first step.


  1. Biotin – Linus Pauling Institute – Oregon State University Micronutrient Information Centre
  2. The enzymes of biotin-dependent CO2 metabolism: What structures reveal about their reaction mechanisms
    Grover L WaldropHazel M Holden, and Martin St Maurice Protein Sci. 2012 Nov; 21(11): 1597–1619.
  3. Cell and Molecular Aspects of Human Intestinal Biotin Absorption1–3
    Hamid M. Said J Nutr. 2009 Jan; 139(1): 158–162.
  4. Biotinidase deficiency: A treatable cause of infantile seizures
    Parveen BhardwajRam Krishan Kaushaland Akshat Chandel
    J Pediatr Neurosci. 2010 Jan-Jun; 5(1): 82–83.
  5. NHS – B vitamins and folic acid
  6. Prevalence of biotin supplement usage in outpatients and plasma biotin concentrations in patients presenting to the emergency department.
    Katzman BM1Lueke AJ1, Donato LJ1, Jaffe AS2, Baumann NA3, Clin Biochem. 2018 Sep; 60:11-16.
  7. Effect of High-dose Biotin on Thyroid Function Tests: Case Report and Literature Review.
    Ardabilygazir A1, Afshariyamchlou S1, Mir D1Sachmechi I2. Cureus. 2018 Jun 20;10(6):e2845
  8. [Apparent thyrotoxicosis in a patient with multiple sclerosis: biochemical assay interference due to high dose biotin use].
    van den Berg R1,2, Slim CL3Lutgers HL1, de Heide LJM1, Wolthuis A3. Ned Tijdschr Geneeskd. 2018 Feb 14;162

How useful was this page?

Tap on a star to rate it!

Average rating 0 / 5. Vote count: 0

No votes so far! Be the first to rate this page.

We are sorry that this page was not useful for you!

Let us improve this page!

Tell us how we can improve this page?

We rely on donations so that we can continue to support and campaign for people with thyroid and related conditions.  If you have found our information helpful, please donate or become a member.