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Hello. My name is 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 cobalamin,
which is also known
as vitamin B12.
0:16
The large vitamin B12 molecule
has cobalt at its centre,
hence the name cobalamin.
Vitamin B12 is essential for
healthy red blood
cell formation,
for DNA synthesis,
for the development,
myelination, and function of
the central nervous system.
It's also a co-factor
for two enzymes,
methionine synthase and
L-methylmalonyl
coenzyme A mutase.
0:43
Vitamin B12 is only
found naturally
in products of animal origin.
It's found in meat,
especially liver,
poultry, fish, milk and
dairy products and eggs.
But it can be added to
breakfast cereals as fortified,
and it's obviously
stated on the label
that it contains vitamin B12.
It is present in
fermented nonmeat foods
such as sauerkraut
because the bacteria
that's used to ferment
the food will make
its own vitamin B12,
and it's found in yeast
products such as Marmite.
1:15
Vitamin B12 is bound
to protein in food,
and this is released
in the stomach,
and then in the duodenum it
binds to intrinsic factor.
This complex, this
B12-intrinsic factor complex
will then bind to receptors
in the terminal ileum
and then it's transported
into the enterocytes.
The absorption of vitamin
B12 is about 50%.
But there is a dose-response;
so it decreases with dose.
It can also decrease quite
significantly with age.
It has been reported that
the bioavailability of vitamin
B12 varies between foods.
For example, dairy products have
a three times higher
bioavailability
than meat, fish, and poultry.
Absorption from vitamin
B12 supplements
is also higher than from foods.
Once it's in the plasma,
