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Iodine is essential for normal growth and development in animals and
man. It is the most heaviest biogenic element with specific affinity to
the thyroid gland, its atomic weight of 127 being twice as high as that
of the heaviest next group of elements such as copper, iron, cobalt, or
zinc, which is about 60.
The total amount of iodine in human body is about 15-20 mg, almost a
half of that being located in the thyroid. The optimum requirement for
normal growth and thyroid function is about 150 µg per day. The thyroid
has to trap about 60 µg iodide per day to maintain the appropriate
supply of thyroxine. Its biological activity in the tissues is again closely
related to iodine, since it consists of deiodination of its tetraiodo-
to triiodo- molecule.
The general deficiency of iodine in the environment and thus also in
human nutrition results in iodine-deficiency disease, which is a risk factor
for the growth and development of about 1 billion people in various continents.
Although impaired development of the central nervous system in fetuses
of iodinedeficient mothers has been recently shown to be the main risk
of iodine deficiency resulting in irreversibly impaired mental and psychoneuromotoric
functions, the best and widely known consequence of iodine deficiency was
and still remains the endemic goiter.
Since the early twenties it is known that the use of iodized salt may
effectively prevent the emergence of endemic goiter, and nowadays this
method is widely used in a majority of industrial and even developing countries.
However, in spite of such unequivocal benefit, some reports started to
appear in the fifties and sixties showing that, under certain circumstances,
an increased intake of iodine could be even harmful. From this view a considerable
uncertainty resulted, namely because it was not clear which is the actual
threshold of a harmful level of iodine intake and thus a widespread view
appeared that any increase in the iodine intake would be hazardous. This
concerns mainly autoimmune thyroiditis or Hashimoto's disease.
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