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,anamino acidnecessary forhealth
-Metabolizing amino acids, cholesterol, and some
fatty acids
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 an RDA. 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 9–13 years: 20 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.
Theapproximatebiotin content in commonfoods 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
