Biotin

Biotin (B7 or vitamin H) is a water-soluble vitamin, which has received publicity for promoting the growth of hair and nails. There are limited studies, which confirm the exact indications of biotin.[1] Biotinidase deficiency is uncommon but has been documented. Frank deficiency of biotinidase may present as conjunctivitis, ataxia, seizure, skin infections, and developmental delay in children.[2] Biotin may have benefits in those suffering from pathologic brittle hair syndrome or uncombable hair syndrome.[3][4] Otherwise, indications for supplementation remain unnecessary in healthy individuals.[1] Biotin deficiencies would require inborn errors of metabolism. Documentation on supplementation in healthy individuals remains unclear. To date, there have been no trials supporting claims of biotin supplementation being used to improve hair quality or quantity or nail growth.[5] The U.S. Food and Drug Administration does not recommend daily biotin usage, although patients who are breastfeeding or pregnant are recommended take from 5 mcg/ to 35 mcg/day. Pregnancy and smoking increase the metabolism of biotin and would require increased intake, although controversial.[6][7] There is limited evidence to suggest biotin can provide a benefit with hair and nail growth. 

Biotin also acts as a coenzyme for multiple carboxylases in humans, and it changes the irreversible carboxylation of acetyl-CoA to malonyl-CoA.[2] These enzymes are vital in numerous metabolic processes. Recently, the new roles of biotin have been acknowledged, in particular, the roles in cell signaling and epigenetic regulation.[8] Biotins mechanism of action occurs by attaching to specific lysine residues.[9] The side effects of ingesting too much biotin could include an upset stomach, although it remains a vitamin with very low side effects. Biotin uptake by human colonic epithelial is a carrier-mediated process.[10] Vitamin B7 is a cofactor for three significant carboxylation reactions, which include the conversion of pyruvate to oxalacetate, acetyl-CoA to malonyl-CoA, and propionyl-CoA to methylmalonyl-CoA. A carboxylase reaction includes the transfer of carbon with the assistance of biotin. Essentially these conversions assisted by biotin break down food into glucose, the primary carbohydrate source for the brain and body. 

Biotin appears to be widely protein-bound.[4] Recommendations for biotin intake range from 5 ug/ to 35 ug/day depending on circumstances. For example, there is no daily recommendation, but biotin use may be appropriate and warranted for a breastfeeding mother due to increased demand for nutrients. Biotin is also required for the normal development of the fetus when the mother is pregnant. When needed, the most common route of administration for biotin is orally, but biotin administration can also be in an IV form. Therefore, there is no indication for daily use by the U.S. Food and Drug Administration, but when indicated, its administration is usually via the oral route. The IV form is for cases where biotin deficiency is apparent and symptomatic. It can also be useful when treating trichothiodystrophy (TDD), a rare autosomal recessive disorder, which appears to benefit from biotin intake. The tablet form of biotin usually comes in forms of 10, 50, or 100 mcg. 

Biotin consumption for beneficial means remains unclear, but it has been considered a very difficult drug to overdose on or cause injury to the body. When taking anticonvulsants such as carbamazepine or phenobarbital, the requirements for biotin increase due to these medications inhibiting uptake into the brush borders of membrane vesicles.[4] Smoking also metabolizes biotin quickly, therefore increased doses may be warranted when indicated if the patient is a smoker. Information on other drug interactions is minimal. There have been no reported injuries for taking too much biotin, but there are documented cases of biotin deficiency. 

Research supporting claims for the use of biotin for nails and hair remains ambiguous, but there has been well-documented research on the interactions of biotin and other drugs. There are no evident contraindications to taking this vitamin. Biotin is a safe and nontoxic vitamin that the body excretes when in excess. There are no known herbal interactions with biotin. Although not a contraindication, it is important to note if a person is taking biotin and smoking, they may require increased doses due to increased metabolism of biotin.