In this era of acrimonious debate about what goes into intelligence,
it may be a surprise to hear that in China alone, 480 million IQ
points have been lost for want of a simple chemical, costing less
than a few cents per person each year.
Around the world, more than 20 million people are less
intelligent than they might have been because they did not receive
this vital nutritional supplement. About 1.6 million people, or a
quarter of the planet's population, are at risk from this deficiency.
The lack of this chemical has caused the IQ bell curve of some
countries to shift thirteen points to the left of where it might have
The substance in question is iodine, the 53rd element of the
periodic table. No longer scarce in the diet of the world's wealthy
nations, this micronutrient is the key to what may be the least
recognized epidemic on the globe.
Micronutrients are substances required in minuscule
amounts to maintain health. A person needs one ten-thousandth
of a gram of iodine a day, two grams over a lifetime.
A worldwide effort is under way to eliminate iodine-deficiency disorders in this decade by fortifying the world's salt
supply. Although there are other ways to deliver iodine, salt is
the cheapest and easiest route.
Iodine deficiency is the world's leading cause of mental
defects. It produces not only severe mental retardation, deaf-mutism and partial paralysis, but also more subtle problems such
as clumsiness, torpor and reduced learning capacity.
Iodine is an essential part of the thyroid hormone, a
substance that contributes to brain development during foetal
life and is the main throttle of metabolism thereafter. Without
enough iodine there cannot be enough thyroid hormone.
The thyroid hormone is made in a gland that wraps around
the front of the neck. A shortage of this hormone causes the thyroid
to grow, a condition known as goiter. Sometimes goiters are
grotesquely large. Other conditions, including hormone excess,
can cause the problem, but iodine deficiency is the most common.
In lower vertebrates, the thyroid hormone is responsible for
such events as the metamorphosis of tadpoles to frogs and the
migration of the juvenile flounder's eyes to one side of its head.
In human beings, the hormone's development activities are mostly
confined to the brain.
A profound lack of the thyroid hormone before birth causes
cretinism (a permanent disability characterized by retardation),
deaf-mutism, muscle rigidity and, often, immature skeletal
Research has shown that giving pregnant women iodine
supplements before the second trimester of pregnancy prevents
cretinism. Supplementation of iodine later, or during infancy, can
decrease, but not eliminate, neurological damage.
Studies have shown that supplementing the diets of those
who are mildly iodine-deficient can measurably improve brain
function. In the most dramatic study, researchers in Malawi (where
in some villages 86 per cent of children were mildly iodine-deficient) supplemented the diet of grade-schoolers with iodine.
The treated group showed significant improvements on
measures of verbal fluency, visual memory and eye-hand
coordination. Although IQ was not measured, the investigators
estimated the average gain was 21 points.
Iodine, however, should not be viewed as some all-purpose
brain food. Taking extra iodine when one is not deficient is not
helpful and can be harmful.