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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,
and I'm going to be talking
to you about sodium.
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Sodium is a major
extracellular electrolyte
and it exists as a fully
water-soluble cation.
It acts as a counter
ion to anions,
for example, chloride for
the maintenance of
electroneutrality.
The gradient between
intracellular and
extracellular sodium
ionic concentrations
and activities
sometimes referred to
as the sodium-potassium pump
underpins cellular
uptake and transport of
water and solutes in all organs.
The wide range of functions
of sodium in the body is
it maintains acid-base balance,
transmitting nerve impulses,
regulating the liquid
flow in and out of cells,
and helping muscles contract.
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Sodium chloride (salt)
is added during
industrial food processing,
also in discretionary use,
table salt in cooking,
or in food preservation.
This is the major source of
dietary sodium in Western diets.
The foods that are specifically
high in sodium include
the following:
processed meats such as
ham, bacon, and sausages,
cheese, canned fish,
olives, seaweed,
snacks and crisps,
highly processed foods
such as ready meals
and condiments
such as soy sauce, Worcestershire
sauce and ketchup.
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Intakes of sodium
are quite variable.
They range from 2
g/day to 14 g/day.
There are wide
variations between
individuals and also
within countries.
For example, Malawi,
Rwanda, and Jamaica
have low intakes of sodium,
whereas Northern China and Japan
generally have high intakes.
Sodium is absorbed in the
small and the large intestine,
and the primary mechanism
is active transport
via a sodium-glucose
transporter.
There are other
mechanisms which include
a sodium-hydrogen exchanger
and also passive diffusion.
Absorption is very high;
It's around 96% even
at very high intakes.
The main excretory route
for sodium is urine.
The typical total body
content of sodium is
