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It
is widely believed by many authorities that iodine deficiency should never be
seen in the affluent West, although this problem affects millions throughout the
developed world.
Some nutritionists argue,
however, that this conventional view is too optimistic, because the content of
all minerals in foods is heavily dependent on the mineral content of the soil
from which those foods are derived.
The assumption must therefore be that the continuing de-mineralisation of farm soils has led to a reduction in the
amount of dietary iodine commonly consumed.
Fish
and other seafood, however, remain a relatively rich source because these ocean
creatures concentrate the sea’s iodine in their flesh. Though not commonly eaten in the West,
seaweed, or kelp, is also an excellent source of iodine for this reason, and is
readily available in the form of a dietary
supplements. Dairy products
and certain meats may also be a good source, particularly where iodine is
routinely added to farm animal feed.
But in countries, including most of
So
even in the West, those not including fish or seafood in their diets, and not
using iodised or sea salt, may be at real risk of
deficiency. In an effort to compensate for low
levels of dietary iodine, the mineral has been routinely added to ordinary table
salt in the
Iodine, however, cannot in any case
be regarded as a luxury.
Its
essential function
lies in the production of the vital thyroid hormones; thyroxine, sometimes known as T4, and tri-iodothyronine, or T3.
And as is well known, these hormones are crucially important in ensuring
a healthy metabolic rate and the release of energy from food; so an underactive thyroid gland is commonly the villain in cases
of excessive weight gain, particularly where this of sudden onset, and in cases
of difficulty in losing weight even when following a sensible reducing programme. A
healthy thyroid gland is also crucial for the optimal functioning of the immune
system.
But perhaps even more importantly, iodine deficiency is also known as a major cause of avoidable brain damage; a problem which the World Health Organisation has estimated to affect an astonishing 50 million people worldwide. Sadly, many of these cases occur in children whose mothers were iodine deficient in pregnancy, resulting in a condition of severely retarded brain development known as congenital hypothyroidism, or “cretinism”. Even where such catastrophic consequences are avoided, iodine deficiency in childhood may also have serious effects on the developing brain, leading to low energy and motivation for learning, and measurable impairment of IQ scores.
Since 2001 the Food and Nutrition Board of the US Institute of Medicine (FNB) has prescribed a Recommended Dietary Allowance for iodine of 150 mcg for all individuals over 14, rising to 220 mcg for pregnant women and 290 mcg for those breastfeeding. Somewhat confusingly, however, an excessive consumption of iodine is also associated with a malfunctioning or enlargement of the thyroid gland, as well as mouth ulcers, headaches and gastric upsets, and the FNB therefore advises an upper safe limit for daily iodine consumption of 1,100 mcg for adults. Most people eating a conventional Western diet are unlikely to exceed this level.
With
the possible exception of pregnant and breastfeeding women, people in the West
who use liberal quantities of iodised salt as a
regular seasoning are unlikely to need further supplements. But many commercial multi-mineral
preparations contain iodine in reasonable quantities, usually in the form of
potassium iodide, and whilst not perhaps strictly necessary, such supplementary
doses will do no harm and may be regarded as a useful insurance policy given
that, like all minerals needed by the body, iodine functions best in the
presence of adequate supplies of all the others. And it should be particularly noted in
this context that the effects of any deficiency of iodine may be intensified by
any deficiency of selenium, iron or vitamin A.
March 2008
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