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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 vitamin K.
Vitamin K includes
phylloquinone, vitamin K1,
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which is found in green
leafy vegetables and
the menaquinones,
known as vitamin K2,
which are found in
animal-based foods.
So vitamin K acts
as a cofactor of
the enzymatic conversion of
vitamin K-dependent proteins.
These are the gamma-carboxyglutamic
acid (Gla- proteins)
into their active form
by carboxylation of
the glutamine synthetase
residues to Gla.
This is gamma-carboxyglutamic
acid-rich residues
in the amino-terminal domain.
The Gla-proteins are involved
in different
physiological processes.
They're involved in
blood coagulation,
bone mineralisation
and also the control
of soft tissue calcification.
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Dietary sources of vitamin K
are mainly the phylloquinones,
which are vitamin K1,
and the menaquinones,
vitamin K2.
The phylloquinones are
found in vegetables.
The most concentrated
forms are found in
leafy green vegetables and
moderate sources are asparagus,
cabbage and brussel sprouts.
Then there are low sources from
grapes, kiwi, and
avocado, for example.
Vitamin K2, there are very
large amounts found in natto.
This is a fermented soy product
which is consumed in Japan.
Then moderate sauces
are, for example,
various cheeses,
chicken, sauerkraut,
which is fermented
cabbage, and beef.
Then, low sources would
be pork and salmon.
So intakes of vitamin K from
Western diets are
estimated to be
72-196 micrograms per day.
But this is a very
uncertain figure
because the food
databases are incomplete.
We don't know enough about
how much vitamin K there
is in various foods.
We also get
menaquinones produced
by the colonic
bacteria in the gut.
But it's not known
to what extent
or how much these are absorbed.
