Biotin

How much you need

The official Adequate Intake for adults, per day:

These are Adequate Intakes, not Recommended Dietary Allowances — there was not enough evidence to set a requirement, so they were extrapolated by body weight from the amount of biotin in breast milk.

People aged 18 fall in the official 14–18 group — 25 mcg a day for males and females, 30 mcg in pregnancy and 35 mcg when breastfeeding. There is no upper limit at any age. Pregnancy and breastfeeding change what you need — confirm yours with your midwife, obstetrician or doctor.

Upper limit

No upper limit does not mean no risk. High-dose biotin supplements can make some blood tests read falsely high or low — including thyroid tests and troponin, a test for heart attack — and the FDA reports a death after a falsely low troponin result. If you take biotin, tell your doctor before any blood test.

No upper limit has been set for biotin, because there is no evidence in humans that it is toxic at high intakes — several studies found no adverse effects from 10 to 50 mg a day. The risk from high intakes is to laboratory tests, not to the body directly; see Too much, below.

What it does

Biotin is a cofactor for five enzymes that carry out critical steps in the metabolism of fatty acids, glucose and amino acids ^[1]. It also plays key roles in gene regulation and cell signalling ^[1]. Most of the biotin in food is bound to protein and released during digestion; it is absorbed in the small intestine and mostly stored in the liver ^[1].

Forms

Biotin is sold alone, in B-complex supplements and in some multivitamins ^[1]. Free biotin taken by mouth is completely absorbed, even in doses of up to 20 mg a day ^[1].

Where it comes from

1. Beef liver, cooked3 ounces30.8 mcg
2. Egg, whole, cooked1 serving10 mcg
3. Salmon, pink, canned in water3 ounces5 mcg
4. Pork chop, cooked3 ounces3.8 mcg
5. Hamburger patty, cooked3 ounces3.8 mcg

How these five were chosen: The five foods with the most biotin per serving in the NIH fact sheet's food table. Fortified foods are marked.

Getting the most from it

Avidin, a protein in raw egg whites, binds tightly to biotin and stops it being absorbed; cooking destroys avidin ^[1]. Canning and some other processing can reduce the biotin in food ^[1].

In the United States

There are no nationally representative estimates of biotin intake in the United States, but in other Western populations average intake from food is about 35 to 70 mcg a day, suggesting most people get enough ^[1].

Who is most likely to run low

• People with biotinidase deficiency, a rare inherited disorder that stops the body releasing free biotin; all U.S. newborns are screened for it, and lifelong biotin from birth prevents its symptoms ^[1]
• People with chronic alcohol exposure, which inhibits biotin absorption — blood biotin is low in 15% of people with chronic alcoholism ^[1]
• Pregnant and breastfeeding women — at least a third of pregnant women develop marginal deficiency despite normal intakes, although the clinical significance is not yet understood ^[1]

What deficiency looks like

Deficiency is rare, and severe deficiency has never been reported in healthy people eating a normal mixed diet ^[1]. Its signs appear gradually and include thinning hair that can progress to loss of all body hair; a scaly red rash around the eyes, nose, mouth and genitals; conjunctivitis; acid build-up in the blood and urine; seizures; skin infection; brittle nails; and, in adults, depression, lethargy, hallucinations and tingling in the hands and feet ^[1].

What the evidence supports, and what it doesn't

Established. Biotin is an essential cofactor for enzymes in fat, glucose and amino acid metabolism ^[1]. In biotinidase deficiency, oral biotin started at birth, before symptoms develop, and continued for life prevents the disorder's neurological and skin symptoms ^[1].

Not supported by trials. Hair, skin and nails in healthy people: biotin is widely promoted for them, but the claims rest, at best, on a few case reports and small studies ^[1]. Evidence for hair comes only from case reports in children with a rare hair-shaft disorder, and for skin only from case reports in infants ^[1].

Mixed. Brittle nails: three small studies without a placebo group, none reporting participants' starting biotin status, gave 2.5 mg a day for several months; in one, 41 of 45 patients had firmer, harder nails, and in another, 22 of 35 improved ^[1].

Too much

There is no evidence that biotin is toxic at high intakes, and doses up to 200 mg a day by mouth have caused no symptoms of toxicity in people with biotinidase deficiency ^[1]. The risk is to laboratory tests: high intakes, and potentially even intakes above the Adequate Intake, can make tests that use biotin-streptavidin technology — common for thyroid hormones, vitamin D and other measures — read falsely high or low ^[1]. Case reports describe results falsely suggesting Graves' disease and severe hyperthyroidism in people taking 10 to 300 mg a day, and a single 10 mg dose has interfered with thyroid tests taken within 24 hours ^[1]. The FDA reports that a patient with a high biotin intake died after a troponin test for heart attack gave a falsely low result, and advises health care providers to ask patients about biotin supplements ^[1].

Medicines that interact

Anticonvulsants — carbamazepine, primidone, phenytoin and phenobarbital — taken for at least a year were linked to significantly lower blood biotin in a study of 264 people with epilepsy, possibly because they speed biotin's breakdown and reduce its absorption ^[1]. If you take any of these regularly, talk to your doctor or pharmacist about your biotin status, and tell your doctor about any biotin supplement before a blood test.