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 Iodine
- why is an adequate intake important?
Iodine
is found in seafood, iodised salt and some
vegetables. It is important for essential
hormone development in the human body. Inadequate
intake of dietary iodine can lead to an
enlarged thyroid gland (goitre) or other
iodine deficiency disorders. Iodine deficiency
is the world's leading cause of mental retardation
in children.
Iodine
is found in foods as iodide. Our bodies
need it to make thyroid hormones. The thyroid
is a gland in the throat that regulates
many metabolic processes, such as growth
and energy expenditure. The two main thyroid
hormones, thyroxine and tri-iodothyronine,
are synthesised from the amino acid, tyrosine,
and from iodide.
The
thyroid hormones regulate the body's metabolic
rate and promote growth and development
throughout the body, including the brain.
If there isn't enough thyroid hormone circulating
in the blood, the brain sends a chemical
message to the thyroid gland, which then
releases a measured dose of these hormones.
If a person's diet is too low in iodine,
the brain keeps sending chemical messages
to the thyroid in vain. In an attempt to
make more thyroid hormone, the gland gets
larger and larger. This overgrowth of the
thyroid gland is called a goitre.
Long
term deficiency can be serious
An enlarged thyroid gland, or goitre, isn't
the only side effect of inadequate iodine
in the diet. Other symptoms include dry
skin, hair loss, fatigue and slowed reflexes.
In
the developing fetus, baby and young child,
the effects of iodine deficiency are serious,
including stunted growth, diminished intelligence
and retardation. Lack of iodine is a major
problem in developing countries and is considered
to be the world's number one cause of preventable
intellectual disability in children. Vegetarians
may also be at risk of iodine deficiency
if they do not eat seafood. Instead they
can get their iodine from iodised table
salt or seaweed. A study published in Sep-Oct
2003 Annals of Nutrition and Metabolism
showed that 25% of the vegetarians, 80%
of the vegans and 9% of those eating a mixed
diet had low iodine status
Sources
of iodine
Iodine is found in seawater, so any type
of seafood is a rich source of this element,
particularly seaweed (e.g kelp). Despite
coming from the ocean, sea salt is not a
good source of iodine. Iodised salt is perhaps
the most common source of iodine in the
Western diet and can provide enough iodine
to avoid low thyroid activity. Since an
adult only requires around one teaspoonful
of iodine over a lifetime, eating fish once
a week is enough to fulfil the average iodine
requirement.
Some
vegetables also contain iodine, but only
if they are grown in iodine-rich soils.
Certain regions of Australia, such as Tasmania
and the Australian Capital Territory, have
low levels of iodine in the soil.
Iodine
can be neutralised by certain foods
The value of dietary iodine can be reduced
by vegetables from the brassica family,
which includes cabbage, brussels sprouts,
raw turnip, broccoli, and cauliflower. In
circumstances where both large quantities
of these foods are eaten and the levels
of dietary iodine are marginal, goitre could
develop.
Iodine
intake in Australia has dropped
Low dietary levels of iodine were thought
to be a problem in the past or in developing
countries only. However, some researchers
suspect that iodine intake levels in Australia
have dropped considerably, perhaps by as
much as half, over the past few decades.
To find out how big the problem is and what
might be done about it, a nation wide study
is set to start in Australia. Some reasons
for low iodine intake may include:
 A
reduction in the use of salt in cooking
and table salt (particularly iodised salt).
Consuming
most of our salt in processed foods, which
do not contain iodine.
Less
iodine in milk because of changes in treatment
methods.
Iodine
levels in Australian soils may have dropped
How
much iodine do we need
The
receommended daily dietary intake of iodine
in Australia:
150
micrograms for men
120
micrograms for women (150 micrograms during
pregnancy, 170 micrograms during lacatation)
Children
70-150 micrograms
Infants
50-60 micrograms
Excessive amounts of iodine can also lead
to goitre. This has occurred where foods
such as seaweeds, which are rich in iodine,
are commonly eaten. However, it is unlikely
that any harmful effects would occur with
habitual intakes up to 300 micrograms per
day.
One
teaspoon of iodised salt provides 150 micrograms
of iodine
1
serve (100g) of seafood provides about 60
micrograms
100g
of vegetables or meat or eggs provides about
25 micrograms of iodine
100g
of dairy products or bread/cereals provides
about 10 micrograms.
Anyone on a low-salt diet should consider
eating a serve of seafood every week to
make sure their iodine levels are adequate,
particularly pregnant women, as lack of
iodine can retard normal development in
their baby. Vegetarians should get iodine
from iodised salt or seaweed.
Where
to get help
Your
doctor
Dietitian.
Things
to remember
Dietary
iodine is needed to make essential thyroid
hormones.
Inadequate
iodine can cause mental retardation and
stunted growth in children and an enlarged
thyroid gland (goitre) in adults.
Good
sources of iodine include iodised salt and
any type of seafood, including seaweed.
References
Eastman
C. Where has all our iodine gone? MJA 1999;
vol 171:455-456.
Last
Updated: Dec 2003
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