What does biotin do in the body?
Biotin is a water-soluble nutrient, included in the B-vitamin family. It is sometimes called vitamin B7 or vitamin H.
We cannot make biotin, so we must get it from our diets, or from the bacteria that can synthesize it in our guts.
- Needed to make fatty acids, glucose (gluconeogenesis in the liver) in the body.
- Required to metabolize carbs and amino acids, and fatty acid metabolism in the mitochondria (biotin is a required cofactor for several carboxylases used in these processes)
- Required for the metabolism of odd-number fatty acids, cholesterol, and branched chain amino acids.
- Involved in the regulation of gene expression, possibly by attaching to histones, but the significance of this biotinylation process is still up for debate (1).
How is biotin absorbed? (2)
Mostly in the small intestines, both actively and passively (via passive diffusion).
The active transport protein that absorbs biotin in the small intestine is called SMVT (sodium-dependent multivitamin transporter) & is made by the SLC5A6 gene.
SMVT also transports pantothenic acid and lipoic acid.
Absorption is upregulated in people who are deficient (more SMVT is made & placed on the brush border).
Some biotin can also be absorbed in the colon (both from food, and what is produced by bacteria in the gut), but it’s not known whether the bacterial contribution is actually significant to our bodies.
How can you test biotin levels? (3)
The best & most sensitive indicator is PCC activity in the lymphocytes (biotin-dependent enzyme), but this is not a very practical blood test to run. It’s really just used in research (4).
Urinary markers: 3-hydroxyisovaleric acid (3-HIA) & 3-hydroxyisovalerylcarnitine (3-HIA-carnitine) (high levels = biotin deficiency). These are considered to be more sensitive than serum for detecting earlier stages of biotin deficiency (5).
Plasma levels are 3-hydroxyisovalerylcarntine (3-HIA-carnitine) (high levels = biotin deficiency).
Serum biotin levels can be tested, but it is not a very sensitive indicator of biotin status.
Spectracell can also be done to check intracellular levels of biotin (but it is not clear if that would give you information on how biotin is behaving in the rest of the body).
Why might you be deficient in biotin?
- Alcoholism (6)
- Anti-seizure medications (7, 8)
- Bariatric surgery causing malabsorption (9)
- Eating raw egg whites (raw egg whites contain a protein called avidin that binds to biotin & prevents it from being absorbed) (10)
- Elemental diet or formula without biotin (14)
- Genetic disorders of biotin metabolism (Biotinidase deficiency, holocarboxylase synthetase (HCS) deficiency, biotin transport deficiency)
- Lacking enough of the gut bacteria that produce biotin, possibly from antibiotic use (but it is still not clear how significant the bacterial production is for our overall biotin pool) (15, 16)
- Large doses of pantothenic acid (vitamin B5), since it uses the same absorptive site as biotin in the small intestine (17)
- Leiner’s disease (a condition in infants causing severe seborrheic dermatitis and diarrhea) (18)
- Liver cirrhosis (19)
- Long-term TPN that lacks biotin (20)
- Malabsorption (sometimes due to things like celiac disease or Crohn’s that damage the small intestine)
- Pregnancy and breastfeeding (increased need, so easier to become deficient) (21)
- Protein-energy malnutrition (22)
- Smoking (increases biotin use) (23)
- Hair loss
- Impaired immune function
- Loss of taste (9)
- Neurologic dysfunction (depression, lethargy, hallucinations, burning or prickling of extremities)
- Pink eye
- Skin rash (especially around the eyes, nose, mouth, and genitals)
Full blown biotin deficiency with the above symptoms caused by diet alone is considered to be very rare in Western countries, but milder deficiencies can still occur (5).
In the US, the most common causes of biotin deficiencies are genetic and typically detected shortly after birth.
What are the best food sources of biotin?
The USDA doesn’t include biotin in their Food Composition Database, and published lab measurements are widely variable (25).
- Egg (whole or yolk)
- Sweet potatoes
How much biotin do you need each day?
There is no RDA for biotin, just adequate intakes:
- 0-6 months old: 5 mcg/day
- 7-12 months old: 6 mcg/day
- 1-3 years old: 8 mcg/day
- 4-8 years old: 12 mcg/day
- 9-13 years old: 20 mcg/day
- 14-18 years old: 25 mcg/day
- 19+ years old: 30 mcg/day
- Pregnant: 30 mcg/day
- Breastfeeding: 35 mcg/day
It is generally considered that people in Western cultures get enough biotin, with intake estimates between 35-70 mcg per day (28)
Is there such a thing as biotin toxicity?
There is no Tolerable Upper Intake Level for biotin.
Studies have used 5mg per day for up to 2 years without any adverse effects reported (29).
Most multivitamins contain much less than that (typically no more than 1g).
How much biotin is required to replete a deficiency?
There really is no consensus on this topic.
Ideally, you should figure out the root cause of the deficiency (see above), and address that whenever possible.
Genova’s NutrEval organic acid testing results recommend 200 mcg per day for a moderate deficiency and 400 mcg per day for a significant deficiency (30).
What biotin supplements are recommended?
Many multivitamins contain more than enough biotin to meet your daily needs.
- Pure Encapsulations O.N.E multivitamin (300 mcg per 1 capsule)
- Thorne Basic Nutrients 2/day (500 mcg per 2 capsules)
Biotin is also sold as a stand-alone supplement, but I would be wary of taking it alone since it competes w. pantothenic acid and lipoic acid for absorption, and you don’t want to cause another deficiency by accident.
How does biotin relate/interact with other nutrients?
Biotin & B12: If biotin is low, it could cause low levels of urinary MMA (methylmalonic acid, a marker of B-12 status on organic acid tests). This is because the conversion of propionyl-CoA to MMA requires biotin. This could mask a B-12 deficiency.
NOTE- biotin can interfere with some lab tests (31):
- May cause falsely low troponin (heart attack indicator), TSH, thyroglobulin, FSH, LH, insulin, and autoantibody readings.
- May cause falsely high free T3, free T4, testosterone, estradiol, and cortisol readings.
- Can lead to incorrect treatment after a heart attack, or even a misdiagnosis of Grave’s disease (high fT4 and fT3, positive TSH receptor antibodies and low TSH)
- Probably wise to NOT take any supplements that contain biotin for a few days before the blood draw (studies show it typically clears from the body in 24 hours but could take longer for mega doses)
Biotin & Pantothenic acid: Share the same transporter in the small intestines, so mega doses of either can cause a deficiency of the other nutrient.