Iodine Deficiency And Excess
Iodine is the cause of more thyroid problems than all other food
substances combined. You can get sick from eating either too much
or too little iodine. In a few countries, especially in remote mountainous
areas where the daily iodine intake is less than 25 micrograms per
day, we find the most severe forms of hypothyroidism including cretinism.
This tragic disorder results from extreme iodine deficiency - affected
children are born with such marked mental and physical retardation,
including deaf mutism and dwarfism, that they never can be productive
members of their society.
The worldwide problem of iodine deficiency is much bigger and extremely
serious. One billion people (one-fifth of the world's population)
do not get enough iodine in their diets, and countless population
studies have shown that they have thyroid-related problems. In addition
to unsightly goiters, they experience increased infant mortality,
infertility, impaired growth, and frequent or endemic hypothyroidism.
Most harmful are the widespread milder forms of developmental retardation
that cause poor performance in school and in the workplace. These
factors are reflected in impaired social and economic development.
In fact iodine deficiency is the leading cause of preventable mental
deficiency in the world today.
The map shows that iodine deficiency is found almost everywhere
in the world except North America. The state of dietary iodine in
the former Soviet Union is not well known. However, there is some
data that suggests that lack of iodine is common in some areas,
and may have worsened the effect of the Chernobyl accident on inhabitants
of that region. Lacking normal amounts of dietary iodine, their
thyroid glands absorbed more radioactive iodine from fallout and
thus increased their subsequent risks for thyroid failure and thyroid
cancer.
An important international effort is now underway to eradicate
iodine deficiency worldwide by the year 2000. Led by the International
Council for the Control of Iodine Deficiency Disorders, such agencies
as UNICEF, the World Health Organization, the World Bank, and the
Thyroid Foundation of America are supporting programs to correct
iodine deficiency by adding iodine to salt and city water supplies,
and by individual treatments such as the administration of iodized
oil orally or by injection. Here is a wonderful opportunity for
you to help a most worthy cause. For more information contact the
ICCIDD or TFA at the addresses or telephone numbers listed in the
back of this book.
In contrast, inhabitants of the United States, Canada, Japan, and
certain other countries eat more iodine than is really necessary.
The Food and Nutrition Board of the National Research Council has
recommended a daily intake of 150 to 300 micrograms of iodine per
day. If you live in the United States your daily dietary iodine
intake is probably between 200 and 700 micrograms per day, because
extra iodine has been added to bread, milk, salt, and other foods
that you consume frequently.
In countries where seaweed or dulse is eaten, the consumption of
iodine may be much higher. One study found that the inhabitants
of the Japanese island of Hokkaido who consume large quantities
of a seaweed called kombu take in more than 200 milligrams (200,000
micrograms) of iodine per day, a thousand times the recommended
daily requirement. Although there is a 10 percent incidence of thyroid
enlargement or goiter on Hokkaido, the inhabitants do not appear
to have an increased risk for other thyroid problems. Normal individuals
seem to have the ability to control the amount of iodine that actually
enters their thyroid gland even if their diet is supplemented with
extra iodine. However, as shown in Table 4, if you have a problem
with your thyroid, that problem could make you more likely to develop
a change in thyroid function if you take in too much iodine in your
diet or in other ways. That would be true, for example, if you ever
had hyperthyroidism due to a generalized overactivity of your thyroid
gland (diffuse toxic goiter or Graves' disease) or if you have a
low-grade inflammation of your thyroid known as chronic lymphocytic
thyroiditis (Hashimoto's disease). Either condition would give you
a tendency to develop hypothyroidism if you were exposed to even
a modest amount of extra iodine. In fact, patients who have had
Graves' disease have become hypothyroid after ingesting as little
as 18 milligrams of iodine per day.
Unborn babies are also very sensitive to iodine excess. Therefore,
if you are pregnant and ingest large quantities of iodine in the
form of a medication, kelp, or another form of seaweed, you risk
having your baby born with a goiter and possibly with an underactive
thyroid as well. A large goiter could compress the baby's windpipe
and interfere with breathing. Moreover, since iodine can also be
transmitted from mother to child in breast milk, you should avoid
health foods and medications that contain extra iodine while nursing
your baby.
An abrupt increase in dietary iodine can cause hyperthyroidism
in people living in iodine-deficient areas of the world. "Epidemics"
of hyperthyroidism have been seen in several countries when iodine
was added to the national diet to correct a long-standing problem
of wide-spread iodine deficiency. This happened in the U.S. in the
1920s when health authorities added iodine to salt.
Hyperthyroidism caused by excess iodine also has been observed
in the United States and other parts of the world where dietary
iodine is sufficient. In such areas, older patients with lumpy thyroids
(nodular goiters) are those most likely to be affected by an increase
in iodine intake. Moreover, since these patients tend to be elderly,
they are more likely to have complications from the rapid pulse
or irregular heart rhythm that may happen when their thyroid becomes
overactive.
Therefore, if you have Graves' or Hashimoto's disease, are pregnant
or nursing a baby, or if you have a nodular goiter, you should try
to avoid an abrupt increase in your iodine intake. Do not eat kelp,
and do read labels on bottles of vitamins and other medications.
If you are having an x-ray for which a dye is given to you by mouth
or by injection, find out if there is iodine in the x-ray dye. This
is likely if the x-ray is of your kidney, spinal canal, gall bladder,
or blood vessels. This is not to say you cannot take a medication
that contains iodine or that you shouldn't have one of these special
x-rays. Rather, if that is your situation, your doctor may choose
to examine you after you take the medication or have the x-ray to
be sure that your thyroid function has not changed.
The natural iodine of most foods is low. It is highest in seafoods,
and there are variable amounts of bread, miIk, eggs, and meat. Fruits
contain little iodine, as do vegetables with the exception of spinach.
The exact amounts of iodine in these foodstuffs vary so widely and
depend on so many factors that it is no longer possible to make
a satisfactory list of the iodine content of foods. Instead, the
message here is to eat a "regular diet" during pregnancy
and while breast-feeding or if you know you have a thyroid condition.
You do not need to avoid iodized salt, bread, and seafood—just
don't take in extra iodine if possible in special foods like kelp.
Some medications which contain a lot of iodine are important treatment
for critical problems. A good example is the heart drug amiodarone
which physicians are using increasingly to stabilize life-threatening
heart rhythm problems. Each tablet contains 75 milligrams of iodine
and the average person taking the drug gets about 9 milligrams of
extra iodine released into their bloodstream every day. If you live
in the United States and need to take amiodarone, you have about
a 20 percent chance of developing hypothyroidism, and a slight risk
for hyperthyroidism. Since such a change in thyroid function may
not occur immediately, your physician will likely check your thyroid
periodically with a TSH blood test. Similarly, other foods or necessary
medications can be used under your doctor's supervision.
If you or your physician want to know more about your iodine intake,
the best thing to do is to measure the iodine content of your urine.
In a general way the amount of iodine in your urine is equal to
the amount you take in from all sources, including food, medications,
and special x-ray dyes. Such a test could be helpful if you are
pregnant and want to know exactly how much iodine you are taking
in. However, in most cases that information is far less important
than a measurement of your thyroid hormone and TSH blood levels.
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