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Most countries in the world, including Australia, are signatories to
the United Nations-sponsored "Declaration for the Survival,
Protection and Development of Children", which states that "every
child has the right to an adequate supply of iodine to ensure its normal
development".1 One teaspoon of iodine is all
a person requires in a lifetime, yet iodine deficiency at critical
stages of development in fetal life and early childhood remains the
world's single most important and preventable cause of mental
retardation.2
For the past three to four decades iodine deficiency has not been of
significant concern in Australia (except in Tasmania); it was
considered largely a problem of developing countries. That is what we
thought until Gunton and colleagues give us a wake-up call with their
article in this issue of the Journal 3. They
found evidence of mild to moderate iodine deficiency in pregnant
women, patients with diabetes and a small group of volunteers
attending a Sydney teaching hospital. In their study, median urinary
iodine concentrations ranged from 64 µg/L in the volunteers to 104
µg/L in pregnant women. The World Health Organization's standard for
iodine-deficiency disorders in population surveys recommends that
a median urinary iodine concentration above 100 µg/L is evidence
against significant iodine deficiency in that
population.4 Other population
indicators of iodine deficiency, including total goitre rates in
school-age children and serum thyrotropin (TSH) levels in the
newborn, were not assessed in the Sydney study. The data of Gunton and
colleagues indicate that the pregnant women they tested are
ingesting less than half the recommended iodine intake in pregnancy
of 200 µg/day. Although this study was not a national survey, and the
sample size was small, the findings are alarming and raise concern
that a major public health problem may be developing in the Australian
community which could put future generations at risk of
iodine-deficiency disorders.
The key factor in the genesis of iodine-deficiency disorders is
decreased production of thyroxine from the thyroid gland. While
endemic goitre is the most easily recognised and best-known
consequence of iodine deficiency, it is probably the least
important. At critical periods in fetal development and in early
childhood, biochemical hypothyroidism, due to iodine deficiency,
results in a wide range of devastating and irreversible effects now
known as iodine-deficiency disorders.5 More recently, we have come
to appreciate that there is a general diminution in intelligence in
iodine-deficient communities such that iodine deficiency is
considered to be the commonest cause of preventable intellectual
disability worldwide.2 Further, there is now very
good evidence that a small decrease in serum free thyroxine level
during pregnancy, either because of iodine deficiency or thyroid
disease, is an important risk factor for impaired psychomotor
development in infants.6,7 The recent demonstration
of intellectual impairment in the children of American women who had
mild hypothyroidism in pregnancy highlights the need for better
detection and treatment of hypothyroidism in early pregnancy,
irrespective of its cause.8
Tasmania is the only Australian State where regular surveillance of
iodine nutrition is undertaken and records are maintained. Other
data are available from the Australian Centre for Control of Iodine
Deficiency Disorders (ACCIDD), located at Westmead Hospital, which
has performed sporadic surveys of urinary iodine excretion levels in
small samples of Australians for the past two decades. In 1992 we
reported that the mean urinary iodine excretion level in Sydney
residents was 180 µg/L, and over 200 µg/L in Tasmanian
children.9 Since then, our sporadic
surveys have shown a gradual but sustained decline in urinary iodine
excretion levels in Sydney residents. We recently found similar
results to those of Gunton et al 3 in a survey of primary
schoolchildren from western Sydney who had a median urinary iodine
concentration of 84 µg/L, and in 16% of whom the iodine concentration
was less than 100 µg/L. Further, unpublished results we obtained in
healthy pregnant women were also very similar to those of Gunton et al,
indicating that widespread mild iodine deficiency threatens to
affect the most vulnerable in our community.
Why is our iodine intake decreasing in Australia? Gunton and
colleagues implicate a combination of factors. Firstly, for over
three decades, we have been dependent on iodine in milk contaminated
by cleaning solutions used in the dairy industry; these solutions are
gradually being replaced by others which leave less iodine in milk.
Secondly, we seem to be using less iodised salt, through a combination
of purchasing uniodised salt for domestic consumption, probably
decreasing our salt consumption, and consuming most of our salt in
processed foods, which, as far as we can ascertain, is uniodised. The
problem is not unique to Australia, as similar downward trends in
iodine intake have recently been noted in other developed countries
such as the United States10 and New
Zealand.11
What actions should be taken in response to these findings? Firstly,
we need more information through a national survey of urinary iodine
excretion and goitre rates to determine the status of iodine
nutrition throughout Australia. Secondly, we need to educate the
population and healthcare providers about the insidious and harmful
effects of iodine deficiency, especially during pregnancy and early
childhood. Finally, we must institute effective and sustainable
means of iodine supplementation to our whole community through
legislating for universal salt iodisation, so that all salt used for
human and animal consumption in Australia is iodised. Iodising all
edible salt will cost less than 10 cents per person annually. In the
past this intervention has been viewed as politically unacceptable,
but the debate was conducted with a view to eliminating endemic goitre
without any real understanding of the often subtle, but devastating,
consequences of impaired brain development. In the interim, every
effort should be made to ensure every pregnant woman ingests an
adequate amount of iodine to ensure her unborn child experiences
normal mental development. Until we have educated the population as a
whole about the risks of iodine deficiency and instituted mandatory
iodisation of all salt for human and animal consumption, it may be
prudent to recommend supplementary iodine for all pregnant women
from the time of conception until weaning of the infant.
Creswell J Eastman, AM
Director, Institute of Clinical Pathology and Medical Research
Westmead Hospital, Westmead, and Clinical Professor of Medicine
University of Sydney, Sydney, NSW
- World Declaration on the survival, protection and development of
children and a plan of action for implementing the world declaration
on the survival, protection and development of children in the 1990s.
New York: United Nations, 1990.
-
World Health Organization. Progress towards the elimination of
Iodine Deficiency Disorders (IDD). WHO/NHD/99.4. Geneva: WHO,
1999.
-
Gunton JE, Hams G, Fiegert M, McElduff A. Iodine deficiency in
ambulatory patients attending a Sydney teaching hospital: Is
Australia truly iodine replete? Med J Aust 1999; 171:
467-470.
-
World Health Organization. WHO, UNICEF, ICCIDD. Indicators for
assessing iodine deficiency disorders and their control through
salt iodisation. WHO/NUT/94.6. Geneva: WHO, 1994.
-
Boyages SC. Clinical Review 49, Iodine deficiency disorders. J
Clin Endocrinol Metab 1993; 77: 587-591.
-
Pop VJ, Kuijpens JL, van Baar AL, et al. Low maternal free thyroxine
concentrations during early pregnancy are associated with impaired
psychomotor development in infancy. Clin Endocrinol 1999;
50: 149-155.
-
Haddow JE, Palomaki GE, Allan WC, et al. Maternal thyroid
deficiency during pregnancy and subsequent neurological
development of the child. N Engl J Med 1999; 341: 549-555.
-
Utiger RD. Maternal hypothyroidism and fetal development. N
Engl J Med 1999; 341: 601-602.
-
Eastman CJ. The status of iodine nutrition in Australia. In:
Delange F, Dunn JT, Glinoer D, editors. Iodine deficiency in Europe --
a continuing concern. New York: Plenum Press, 1993: 133-139.
-
Dunn JT. What's happening to our iodine? [editorial]. J Clin
Endocrinol Metab 1998; 83: 3398-3400.
-
Thomson CD, Colls AJ, Conaglen JV, et al. Iodine status of New
Zealand residents as assessed by urinary iodide excretion and
thyroid hormones. Br J Nutrition 1997; 78: 901-912.
©MJA 1999
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