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Biotin, also known as vitamin H or vitamin B7, belongs to the group of B-complex water-soluble vitamins. Humans make only a small amount of biotin, so most biotin must come from the foods they eat. Biotin is involved in conversion of carbohydrates, fats, and protein into usable energy in the body.
Biotin joins with enzymes that regulate the breakdown of foods and their use in the body. Some researchers believe that biotin also plays a role in the duplication and “reading” (replication and transcription) of deoxyribonucleic acid (DNA—genetic material). Biotin is often promoted as a dietary supplement to help improve the strength of fingernails and prevent hair loss. These claims are unproven.
Biotin is one of the less familiar B vitamins. It was discovered in the 1930s by researchers experimenting with different diets for chickens and rats, and later it was discovered to be essential to human health. Bacteria, yeasts, mold, algae, and some plants make biotin. The human large intestine (colon) contains some bacteria that synthesize biotin. Researchers believe that a portion of this biotin is absorbed into the bloodstream, but they are uncertain how much or how available it is to the body.
Biotin is essential to life because it combines with four different enzymes that control different metabolic reactions related to energy production and building new molecules from simple nutrients. These are:
- Forming glucose from fats and amino acids (but not from carbohydrates)
- Building fatty acids
- Synthesizing leucine, an amino acid necessary for health
- Metabolizing amino acids, cholesterol, and some fatty acids
(Illustration by GGS Information Services/Thomson Gale.)
Some researchers have found that biotin binds to proteins called histones that open up chromosomes so that their DNA becomes accessible and can be copied. If this is true, then biotin could play a role in gene expression.
Dietary supplement makers promote biotin to treat brittle fingernails, dry skin, and to prevent hair loss. It is sold as a dietary supplement in capsules or tablets, either alone, in a multivitamin, or combined with brewer’s yeast. Biotin is also added to cosmetics and skin creams. In animal studies, biotin improves the condition of horse hooves, but no controlled studies have shown the same effect on human fingernails. Biotin deficiency does cause hair loss, but there is no proof that supplemental biotin prevents hair loss.
Normal biotin requirements
The United States Institute of Medicine (IOM) of the National Academy of Sciences has developed values called Dietary Reference Intakes (DRIs) for vitamins and minerals The DRIs consist of three sets of numbers. The Recommended Dietary Allowance (RDA) defines the average daily amount of the nutrient needed to meet the health needs of 97–98% of the population. The Adequate Intake (AI) is an estimate set when there is not enough information to determine anRDA. The Tolerable Upper Intake Level (UL) is the average maximum amount that can be .
taken daily without risking negative side effects. The DRIs are calculated for children, adult men, adult women, pregnant women, and breastfeeding women.
The IOM has not set RDA values for biotin because of incomplete scientific information. Instead, it has set AI levels for all age groups. AI levels for biotin are measured by weight (micrograms or mcg). No UL levels have been set for biotin because large doses of biotin do not appear to cause any side effects.
The following are the AIs for biotin for healthy individuals:
- Children birth-6 months: 5 mcg
- Children 7-12 months: 6 mcg
- Children 1-3 years: 8 mcg
- Children 4-8 years: 12 mcg
- Children 14-18 years: 25 mcg
- Adults age 19 and older: 30 mcg
- Pregnant women: 30 mcg
- Breastfeeding women: 35 mcg
Sources of biotin
Biotin is found in small quantities in many foods. Bacteria in the large intestine also make biotin. Unlike some vitamins, biotin is recycled and reused by the body. Daily intake does not need to be high because only small amounts are lost in urine. Biotin is stable and little is lost when foods are exposed to heat, light, or air.
The approximate biotin content in common foods is:
- Bread, whole wheat, 1 slice: 6 mcg
- Egg, 1 cooked: 25 mcg
- Liver, cooked, 3 ounces: 27 mcg
- Chicken, cooked, 3 ounces: 3 mcg
- Pork, cooked, 3 ounces: 2 mcg
- Salmon, cooked, 3 ounces: 4 mcg
- Swiss chard, cooked, 1/2 cup: 5.2 mcg
- Cauliflower, raw, 1/2 cup: 2 mcg
Biotin deficiency is very rare worldwide. Only a few conditions are known to cause biotin deficiency. Two rare inherited genetic disorders cause the body to need excessive amounts of biotin. These disorders are treated with high-dose biotin supplements. Prolonged (months or years) consumption of raw egg whitescan also cause a deficiency. A protein in raw egg whites binds biotin and makes it unavailable to the body. Cooking the egg releases the biotin. Receiving all nutrition through intravenous feeding (total parenteral nutrition or TPN) for an extended period may also lead to a shortage of biotin in the body.
Symptoms of biotin deficiency include skin and hair problems, such as a red scaly rash on the face, increased susceptibility to fungal infections, brittle hair, and hair loss. Individuals may also develop seizures, problems with coordination, and muscle cramps. Biotin deficiency has not been known to cause death. These symptoms have many other causes that should be considered first because biotin deficiency is so rare.
In many species, pregnant animals who are biotin deficient give birth to offspring with birth defects at a higher rate than animals who have adequate levels of biotin. The same effect has not been seen in humans. However, blood levels of biotin tend to drop in pregnant women, causing concern among researchers that pregnant women may develop marginal biotin deficiency with no visible symptoms. Dietary supplements of biotin are not routinely recommended for women who are pregnant, but these women should make a special effort to get an adequate intake of 30 mcg biotin daily through diet. Pregnant and breastfeeding women should not take a biotin dietary supplement unless directed by their healthcare provider.
Biotin is known to interact with a few drugs and dietary supplements
- Antibiotics taken over a long period may reduce the amount of bacteria in the large intestine that synthesize biotin.
- Long-term use of drugs used to prevent seizures such as phenytoin (Dilantin), primidone (Mysoline), car-bamazepine (Tegretol), phenobarbitol (Solfoton) and possibly valproic acid cause a reduction in the blood level of biotin.
- High doses of pantothenic acid may decrease the amount of biotin absorbed from the large intestine.
No complications are expected from biotin. Even when large doses are taken for long periods, there are no reported side effects.
Biotin deficiency is rare and biotin excess is so benign that parents should have almost no concern about their children’s biotin needs being met by diet.
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