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Hello. My name is Susan
Fairweather-Tait.
I'm Professor of Human Nutrition
in the Norwich Medical School
at the University of
East Anglia in the UK.
I'm going to be
talking about biotin,
which is one of the B vitamins
sometimes known as vitamin B7.
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Biotin is a
water-soluble vitamin,
and a cofactor for
enzymes involved in
the synthesis of fatty acids,
the catabolism of
branched-chain amino acids
and gluconeogenesis.
It transfers carbon dioxide
in a small number of
carboxylation reactions.
It acts via cell
surface receptors
to regulate the
expression of key enzymes
involved in glucose metabolism.
In summary, biotin helps make
fatty acids and glucose,
and it helps to convert
nutrients into energy.
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The richest food sources
of biotin are liver,
which contains 4.16 micrograms
per 100 grams of wet weight,
and eggs, which contain
about half that amount,
2.14 micrograms per 100
grams of wet weight.
Then the other
foods which contain
reasonable amounts of
biotin are mushrooms,
cheese, meat, fish, and
poultry, and some vegetables.
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Most biotin in foods is
present as biocytin,
which is released
on proteolysis,
then hydrolysed
by biotinidase in
the pancreatic juice and
intestinal mucosal secretions.
Free biotin is absorbed
by two mechanisms.
Firstly, there's a saturable
carrier-mediated process,
which is reliant on
the sodium-dependent
multivitamin transporter.
Secondly, there's
passive diffusion.
This only occurs when there
are large doses of biotin.
Faecal excretion of
biotin has been observed
to be about 3-6 times
higher than intake,
and this is due to the
production of large amounts
of biotin by the
intestinal microbiota.
However, the extent to which
the biotin that's absorbed
from the large intestine
that is produced
by the microbiota,
we don't know how
much is absorbed
and how much it contributes
to biotin requirements.
In the plasma, biotin is
transported as free biotin.
