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0:00
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 D.
0:14
The principal function
of vitamin D is
the regulation of calcium
absorption and homeostasis.
The active metabolite,
calcitriol,
acts to increase the plasma
concentration of calcium
by increasing
intestinal absorption,
reducing urinary excretion,
and mobilizing the
mineral from the bone.
Calcitriol also has a role in
the regulation of cell
proliferation and differentiation.
So you can see there are
many roles of vitamin D.
It's involved in regulation
of immune function,
regulation of phosphorus and
calcium homeostasis,
insulin secretion,
the control of cell
proliferation,
stimulation of cell
differentiation,
induction of apoptosis,
regulation of muscle
calcium transport,
and is involved in growth
and bone mineralisation.
1:01
Vitamin D isn't
present in many foods.
Vitamin D3, which
is cholecalciferol,
is found in fish oils,
liver, eggs and butter.
Vitamin D2, which is
called ergocalciferol,
is found in mushrooms exposed to
UV-B (ultraviolet B) light.
It's also found in fortified
foods, most often milk,
margarine and/or butter,
and in breakfast cereals,
and in dietary supplements.
But increasingly,
we're replacing
vitamin D2 with vitamin D3,
because D3 is slightly
better absorbed than D2.
1:38
So vitamin D from foods is
absorbed throughout
the small intestine.
It's mostly in the
distal small intestine.
And it's absorbed
in lipid micelles
and incorporated
into chylomicrons.
Therefore, fat needs
to be consumed
at the same time as vitamin D.
The absorption efficiency
of vitamin D is high;
it's about 80%,
and there's little discrimination
between D2 and D3.
As I said earlier, D3 is slightly
better absorbed than D2.
So it's the vitamin
type/form which is being
used increasingly for adding
to foods and supplements.
Having talked about
vitamin D in foods,
