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Hello. My name's Susan
Fairweather-Tait.
I'm a professor of
human nutrition in
the Norwich Medical School at
the University of East
Anglia in the UK.
I'm going to be talking
to you about thiamine,
spelled with or without an E,
which is also known
as vitamin B1.
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Free thiamine functions as
the precursor for thiamine
diphosphate, TDP,
which is also called
thiamine pyrophosphate, TPP.
This acts as a coenzyme
for enzymes involved in
carbohydrate and branched-chain
amino acid metabolism
and in energy-yielding
reactions.
TDP is required for
the function of the brain
and the nervous system.
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Thiamine is present in
all plant food sources as
free thiamine, and
it's present in
animal tissues in
phosphorylated forms.
The main food sources include
whole grains, pulses,
potatoes, meat (especially
pork), liver, and fish.
As a water-soluble vitamin,
thiamine is readily lost
through leaching
into cooking water.
It's unstable to light, so
some is lost when foods,
such as baked goods, are
exposed to sunlight.
There are also losses
with food processing.
So alkaline pH, high temperatures,
exposure to sulphites,
all contribute to
significant thiamine loss.
For example, in
potato products that
have been blanched by immersion
in sulphite solution.
Polyphenols, such as
tannic acid in tea,
will destroy thiamine.
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Thiamine phosphate esters are
hydrolyzed to thiamine (T)
in the intestinal lumen by
intestinal phosphatases in
the brush-border membrane.
Thiamine is absorbed
by active transport in
the duodenum and the
proximal jejunum,
and by carrier-mediated
transport in the colon.
Thiamine is carried across
the mucosal membrane
by transporters,
and either converted to TPP or
transported into the blood.
In healthy subjects,
thiamine absorption is
>95% at intakes <2mg,
and daily intakes in
adults are 1-2mg/d.
Much of the absorbed thiamine
is phosphorylated in the liver,
