Vitamin B7 (Biotin)Vitamin

• Brittle nailsPossibly helps

  Three small studies used 2.5 mg/day for several months, none with a placebo group and none confirming participants' baseline biotin status [1].
  
  One reported nail thickness up 25% immediately after the course, a result that lost significance in a delayed-retest subgroup [1].
  
  In a second, 41 of 45 patients (91%) had firmer, harder nails after about 5.5 months. A third, retrospective, found clinical improvement in 22 of 35 (63%) [1]. ^[1]

• Hair growth in healthy peoplePossibly helps

  The only supporting evidence is case reports in children with uncombable hair syndrome, a rare hair-shaft disorder, where 3-5 mg/day for 3-4 months improved the hair [1].
  
  NIH ODS's own conclusion is that future studies are needed to determine whether biotin helps hair, nail, and skin health, especially in healthy people [1]. ^[1]

• Skin and infant dermatitisPossibly helps

  Evidence here is limited to infant case reports, at 100 mcg to 10 mg/day, describing improvement in rash and dermatitis [1].
  
  No controlled trial in healthy adults backs the skin claims printed on hair-skin-nails labels [1]. ^[1]

• Sources disagree on how thin the hair and nail evidence isPossibly helps

  Same evidence base, two readings, and we are not picking one for you.
  
  NIH ODS calls the hair and nail claims supported at best by a handful of small, non-placebo studies and case reports [1].
  
  StatPearls says flatly that no trials support biotin for hair quality or nail growth in healthy people [4]. ^[4]

• Blood sugar in type 2 diabetesPossibly helps

  Biotin's coenzyme role in glucose metabolism has prompted early interest here [4].
  
  The only evidence StatPearls cites is a rat model. There is no human trial to point to [4]. ^[4]

• Thinning hair, progressing to loss of all body hair as deficiency deepens
• A scaly red rash around the eyes, nose, mouth, and perineum. Combined with a characteristic pattern of facial fat redistribution, this is called "biotin deficiency facies"
• Brittle nails
• Conjunctivitis
• Ketolactic acidosis and aciduria
• Seizures
• Skin infection
• In adults: depression, lethargy, hallucinations, and pins-and-needles in the hands and feet
• In infants: low muscle tone, lethargy, and delayed development^[1]

• Free biotin (standard supplements)Everyday supplementation. No published human study compares standard biotin against liposomal or other enhanced-deliver…

  Elemental content

  Unbound biotin, as sold stand-alone, in B-complex products, and in multivitamins

  Absorption

  Essentially 100% orally bioavailable, holding up even at pharmacologic doses around 20 mg/day [1][3]

  Best for

  Everyday supplementation. No published human study compares standard biotin against liposomal or other enhanced-delivery versions, so no bioavailability upgrade claim is supported [1]

• Protein-bound biotin (from food)Ordinary dietary intake. Medscape's clinical reference is explicit that bound biotin in oral multivitamins does not cor…

  Elemental content

  Biotin attached to food protein, released by gut proteases and the enzyme biotinidase

  Absorption

  Freed in the intestinal lumen first, then absorbed in the small intestine [1]

  Best for

  Ordinary dietary intake. Medscape's clinical reference is explicit that bound biotin in oral multivitamins does not correct the deficit in biotinidase deficiency, where free biotin is used instead [6]

• High-dose hair and nail tabletsNothing established. These are the products behind the lab-test interference problem, some carrying up to 650 times the…

  Elemental content

  Commonly 5,000-10,000 mcg per tablet, versus 10, 50, or 100 mcg in standard tablets [4][7]

  Absorption

  Same route as any free biotin — the issue is the quantity, not the delivery

  Best for

  Nothing established. These are the products behind the lab-test interference problem, some carrying up to 650 times the recommended daily intake [1][2]

• Excess intake

  Biotin is considered very hard to overdose on, and no upper limit exists [1].
  
  StatPearls flags GI upset as the main effect of excess, plus a theoretical caution in diabetes, since biotin has a role in glucose control [4].
  
  One rare case report describes life-threatening eosinophilic pleuropericardial effusion after combined high-dose vitamin B5 and B7 [4]. ^[4]

• Immunoassay lab-test interference

  This is the highest-consequence fact on the page. Many immunoassays — thyroid panels, cardiac troponin, 25-hydroxyvitamin D, other hormone tests — use biotin-streptavidin chemistry [1][2].
  
  Supplement biotin circulating in your blood can push those results falsely high or falsely low, depending on the assay [2].
  
  FDA safety communications from 2017, updated 2019, describe adverse-event reports including one patient death after a falsely low troponin result [2].
  
  A single 10 mg dose distorted thyroid function tests within 24 hours in a published case [1]. In healthy adults, 10 mg/day for one week falsely lowered TSH and NT-proBNP, which could hide thyrotoxicosis or heart failure [1].
  
  Tell whoever orders your bloodwork that you take biotin. This is a testing problem, not a toxicity problem [1][2]. ^[2]

• Biotinidase deficiency

  This rare inherited disorder blocks the release of free biotin from food, so intake looks normal while status is not [1]. All US newborns are screened for it, and without lifelong free biotin it can lead to coma or death [1].
  
  Standard management uses free biotin, typically starting at 5-10 mg/day and sometimes running up to 40 mg/day [6]. ^[1]

• Chronic alcohol use

  Alcohol inhibits biotin absorption. About 15% of people with chronic alcoholism have low plasma biotin [1]. ^[1]

• Pregnancy and breastfeeding

  At least a third of pregnant women develop marginal biotin deficiency despite normal dietary intake [1].
  
  A controlled trial found 300 mcg/day for 14 days significantly reduced 3-hydroxyisovaleric acid, a urinary marker of insufficiency, in pregnant women with elevated levels [8].
  
  What marginal deficiency in pregnancy actually means clinically is still under research [1]. ^[1]

• Smoking

  Smoking speeds up biotin catabolism, so smokers may need more than non-smokers, per StatPearls [4]. ^[4]

• Long-term anticonvulsants

  Long-term carbamazepine, primidone, phenytoin, or phenobarbital was linked to significantly lower serum biotin in a 264-person epilepsy study [1].
  
  The likely mechanism is a combination of faster biotin breakdown and reduced intestinal absorption [1]. ^[1]

Organ meats, eggs, fish, meat, seeds, nuts, and some vegetables such as sweet potato are the strongest sources [1].

NIH ODS keeps the food table, since USDA's FoodData Central does not carry biotin at all [1]. Against the 30 mcg Daily Value, cooked beef liver (3 oz) gives 30.8 mcg, or 103% DV [1].

One cooked egg has 10.0 mcg (33% DV), canned pink salmon (3 oz) 5.0 mcg (17%) [1]. A pork chop or hamburger patty (3 oz) gives 3.8 mcg each (13%) [1].

Roasted sunflower seeds (1/4 cup) 2.6 mcg (9%), cooked sweet potato (1/2 cup) 2.4 mcg (8%), roasted almonds (1/4 cup) 1.5 mcg (5%) [1].

Tuna, spinach, broccoli, cheddar, milk, yogurt, oatmeal, and banana each sit at 1-2% DV per typical serving [1].

Raw egg white is the classic blocker. Its glycoprotein avidin binds biotin tightly and stops absorption in the gut [1].

Cooking denatures avidin and removes that interference, which is why cooked eggs count as a good source [1].

Average intake across Western populations is estimated at 35-70 mcg/day [1]. That implies most people there cover their needs from food alone [1].

No clinical evidence shows time of day changes biotin's absorption or effect. Verywell Health's medically reviewed guidance says studies have not shown any specific time to be more effective [7].

It can be taken with or without food [7]. Some combination products, such as biotin paired with collagen or keratin, carry their own with-food instructions on the label [7].

Biotin is water-soluble and not stored, so the body uses what it needs and passes the rest in urine [1][7]. Daily consistency matters more than the hour [7].

Two practical notes from the same source: pick a fixed time to build the habit, and check your other supplements so you aren't doubling up [7].

One timing caution that isn't about absorption: high-dose biotin can distort lab tests for at least 24 hours, so tell your provider before thyroid or cardiac bloodwork [1][7].