The International Council for the Control of Iodine
Deficiency Disorders (ICCIDD) receives many requests for general information
in nontechnical language about Iodine Deficiency Disorder (IDD) and iodine
nutrition. This article offers answers to some of the more frequent questions:
- What is iodine?
- What does iodine do?
- Why do we need iodine?
- How much iodine should we get?
- Where do we get iodine from?
- What happens if we don't get enough iodine?
- What happens if we get too much iodine?
- How can we tell if we are getting the right amount of iodine?
- How do we adjust iodine nutrition?
- What is being done internationally about iodine deficiency?
- How can countries maintain optimal iodine nutrition?
- How can we find out more?
1. What is iodine? -
Iodine is a chemical element (as are oxygen, hydrogen, and iron). It occurs
in a variety of chemical forms, the most important being:
iodide (I-); iodate (IO3-), and elemental iodine (I2). It is present in fairly
constant amounts in seawater but its distribution over land and fresh water
is uneven. Deficiency is especially associated with high new mountains (e.g.,
Himalayas, Andes, Alps) and areas of frequent flooding, but many other areas
are also deficient (e.g., Central Africa, Central Asia, much of Europe).
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2. What does iodine do? - Iodine is an essential part of the
chemical structure of thyroid hormones. The thyroid is a butterfly-shaped gland
in the front
part of the neck. It makes two hormones (thyroxine (T4) and triiodothyronine
The thyroid hormones are released into the bloodstream and carried by it
to target organs, particularly the liver, kidneys, muscles, heart, and developing
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3. Why do we need iodine? - Because thyroid
hormones are essential to life. The thyroid hormones act in target organs
by influencing many different
chemical reactions, usually involving manufacture of key proteins. The body
proper levels of thyroid hormone to work well.
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4. How much iodine should we
get? - Several international groups have
made recommendations, which are fairly similar. ICCIDD, WHO, and UNICEF
the following daily amounts: age 0-7 years, 90 micrograms (mcg); age
7-12 years, 120 mcg; older than 12 years, 150 mcg; and pregnant and lactating
A recent report by the Food and Nutrition Board, Institute of Medicine,
National Academy of Sciences, USA, offers similar recommendations. It
calculates an "Estimated
Average Requirement" and from that derives an RDA (Recommended Daily Allowance).
However, occasionally sufficient data are not available and instead an "Adequate
Intake" is calculated, which may be set higher than the RDA would
be, for safety. The recommendations for daily intake are as follows:
the AI for
infants 0-6 months is 110 mcg iodine and 7-12 months, 130 mcg; the RDA's
are: 1-8 years old, 90 mcg; 9-13 years, 120 mcg; 14 and older, 150 mcg;
220 mcg; lactation, 290 mcg. The Food and Nutrition Board also sets the
tolerable upper limits of the daily iodine intake as 1.1 mg (1100 mcg)
for adults, with
proportionately lower levels for younger age groups.
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5. Where do we get iodine from? - Most of it comes
from what we eat and drink. Seafood is usually a good source because
the ocean contains
iodine. Freshwater fish reflect the iodine content of the water where
they swim, which
may be deficient. Other foods vary tremendously in iodine content,
depending on their source and what may have been added. Plants grown
soil do not have much iodine, nor do meat or other products from animals
fed on iodine-deficient plants. Because the breast concentrates iodine,
are usually a good source, but only if the cows get enough iodine.
Iodized salt is a special case. With only a few isolated exceptions,
edible salt (sodium chloride) does not naturally contain iodine.
Iodine is added
deliberately as one of the most efficient ways of improving iodine
nutrition. The amount
added varies widely in different regions. In Canada and the United
States, iodized salt contains 100 ppm (parts per million, same as
as potassium iodide (equals 77 ppm as iodide), so two grams of salt
contains approximately the daily recommended amount of 150 mcg iodine.
United States, you can
buy salt that is either iodized or not iodized, and the price is
the same; about 50% of all the salt sold in the U.S. is iodized. In Canada,
salt is iodized. Most other countries add from 10 to 40 mcg iodine
of salt (10-40 ppm). Daily salt intake varies greatly in different
parts of the world, ranging from two to five grams in many western
to 20 grams
in some others. An average figure may be 10 grams per day.
These statements apply only to table salt. Most edible salt is added
at cooking. If present as potassium iodate, as in most countries,
during cooking, depending on how pure the salt is. Many people
get most of their salt from processed foods, especially in developed
countries, and commercial
practices vary as to whether these contain iodine or not.
exposure can come from many other sources. Certain food colorings (e.g.,
erythrosine) contain iodine, although it is only
iodine from skin disinfectants, such as povidone iodine, is absorbed
and reaches the bloodstream. Certain health foods, such as some
types of kelp,
large amounts of iodine. Other sources are dyes used for contrast
in X-ray procedures and medicines, such as Amiodarone (used for
heart failure and
abnormal heart rhythm). People also get iodine from its use in
farm animals, for cleansing
udders or as part of iodine-containing medicines. Iodate has
as a bread stabilizer in commercial baking, although this practice
is less common
now. Many other environmental sources of iodine exist; most of
them are unrecognized or unpublicized.
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6. What happens if we don't get enough iodine? - The
most damaging consequences are on fetal and infant development. Maternal
miscarriages, other pregnancy complications, and infertility.
Thyroid hormones, and therefore
iodine, are essential for normal development of the brain. If
the fetus or newborn is not exposed to enough thyroid hormone,
retardation, even if it survives. Low birth weights and decreased
child survival also result from iodine deficiency. Cretinism
is a very severe
this brain damage; it includes permanent dense mental retardation,
and varying degrees
of additional developmental defects such as deafmutism, short
stature, spasticity, and other neuromuscular abnormalities.
The most visible consequence of iodine deficiency is goiter.
This word means "an
enlarged thyroid." The process begins as an adaptation in which the thyroid
is more active in its attempts to make enough thyroid hormone for the body's
needs, despite the limited supply of raw material (iodine), much as a muscle
gets bigger when it has to do more work. If this adaptation is successful and
the iodine deficiency is not too severe, the person may escape with only an
enlarged thyroid and no other apparent damage from the iodine deficiency. Older
individuals with goiters may develop nodules (lumps) in their thyroids, and
sometimes these can begin making too much thyroid hormone when suddenly exposed
to iodine. This result occurs because these nodules are independent of usual
controls; they make thyroid hormone at their own rate, and may over-produce
it when given more iodine. Also, the nodular goiters in iodine deficiency have
an increased rate of one type of thyroid cancer, called "follicular cancer." Goiters
can sometimes enlarge enough to produce compression of other neck structures
and may need surgical removal for that reason.
In addition to these effects on the individual, iodine deficiency
has adverse consequences for the community. The mental retardation
cover a wide
range, from mild blunting of intellect to cretinism, and a large
part of the population
may have some intellectual impairment. The mean IQ of the deficient
community is decreased by about 13.5 IQ points, according to
one review. Individuals
in these communities have lower educability and lower economic
productivity, and the output of the whole community suffers.
typically occurs after appropriate addition of iodine.
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7. What happens if we get too
much iodine? - Most people
who have previously been iodine sufficient can safely tolerate fairly
mentioned above, some individuals have thyroid nodules that escape
the body's usual
controls, and they can start making too much thyroid hormone
when their dietary iodine
increases, to produce a condition called iodine-induced hyperthyroidism.
Iodine excess can also cause thyroid underactivity, because large
amounts of iodine block the thyroid's ability to make hormone.
Individuals vary widely in their tolerance to iodine. Most people
but there are exceptions. People with a tendency towards so-called
autoimmune thyroid diseases, such as Graves' disease or Hashimoto's
have family members with these problems, may be more sensitive
to iodine. In fact, high iodine intakes in a population are associated
increased incidence of these autoimmune thyroid diseases. Also,
iodine in the population may increase the incidence of papillary
this is not well established. Fortunately, papillary thyroid
cancer is usually a mild form of cancer and rarely causes death.
Most people can tolerate at least 1 mg (1000 mcg) of iodine daily
without adverse effects. People with underlying autoimmune thyroid
or who have previously
been iodine deficient, may tolerate less. Iodine excess is undesirable,
but its consequences are not nearly so severe as those of iodine
deficiency, because the latter affects human development and
can produce permanent
Properly iodized salt will rarely add more than about 300 mcg
iodine daily to the diet. Therefore, concern about iodine excess
a reason to
stop or avoid consumption of iodized salt.
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8. How can we tell if we are getting the right
amount of iodine? - Usually you as an individual won't know how much iodine
in countries like the United States, because iodine appears in
commercial preparations without notice. You can make a rough
on (1) whether you
use iodized salt; (2) how much salt you eat; (3) whether you
take vitamins that contain iodine (many contain 150 mcg); and
much meat, dairy products, or seafood.
For populations, a better way to learn the iodine intake is to
measure the amount of iodine in representative urine samples.
than 90%) of
the iodine you ingest eventually comes out in the urine. Thus,
the concentration of iodine in the urine, even in casual samples,
a good marker for
iodine nutrition. Urine iodine concentration varies with fluid
intake, so these
have limited use for casual samples from an individual, but they
are good for assessing a population group, because individual
variations tend to
average out. A median urinary iodine concentration between 100
and 200 mcg/L is ideal.
The following scale has been used by WHO/ICCIDD/UNICEF to relate
nutrition to urinary iodine concentration:
Median Urinary Iodine
Iodine Intake (mcg/day)
More than adequate
Routine laboratory tests of thyroid function are not as helpful
as the urinary iodine concentration in assessing a population.
hormone or thyrotropin) is a test that is widely used clinically
to assess thyroid function in individuals. TSH is released
into the blood
by the pituitary (an endocrine control gland at the base of
the brain) in response
to the amount of thyroid hormone in the blood stream. TSH tells
the thyroid how hard to work. It bases this decision on how
is present in the blood. When blood thyroid hormone is low,
serum TSH increases
can be used as a measure for inadequate thyroid hormone production.
The serum TSH is the most widely used test for diagnosing thyroid
disease in individuals.
However, the serum TSH is less valuable in recognizing iodine
deficiency, because it can increase but still remain within
the normal range.
An exception is the blood TSH in newborns. Most developed countries
have a system of newborn screening, either with the blood
TSH or thyroxine, to recognize
congenital hypothyroidism. About one out of 4,000 newborns
has congenital deficiency of thyroid hormone production,
usually because the thyroid
is absent or fails
to develop properly. This newborn screening is important
because prompt treatment with thyroid hormone can prevent most or all
of the consequences
thyroid hormone on brain development. Newborn TSH screening
areas with iodine deficiency shows an increase in the number
Usually, this transient hypothyroidism corrects itself, and
most of these
infants do not show brain damage, but there remains a potential
risk for this result,
particularly if they continue iodine deficient during nursing.
Thyroid size is also a useful marker of iodine nutrition,
because the iodine-deficient thyroid enlarges, as described
One way to recognize
goiter is to
feel the thyroid and make an estimate of its size; this
maneuver is quite simple
but fairly crude and not very accurate in detecting slight
enlargement, particularly in children. Use of an ultrasound
machine is simple
and can be done in remote
settings; this measurement provides another good index
of the degree of iodine deficiency.
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9. How do we adjust iodine nutrition? - Salt is the
best vehicle for adding iodine. Everyone needs salt, everyone
eats it, usually
and the technology for iodization is straightforward.
It can be added as potassium
iodide or potassium iodate; the latter is preferred under
conditions of humidity or impurities because of its greater
Most countries have regulations
calling for 20-40 mcg iodine/g of salt (20-40 ppm); thus
if an individual eats 5 g of salt iodized at 30 ppm,
The amount to be added varies for particular populations,
depending on the amount of salt ingested, the purity
of the salt (and
lost between production and consumption), and the amount
of iodine ingested from other sources. In some countries,
the health authorities raise the amount of iodine in
the salt, to provide a constant
adequate daily amount.
Another method for providing iodine to a community is
through the administration of iodized vegetable oil.
developed as an X-ray contrast medium. One milliliter
(one-fifth of a teaspoon)
contains about 480 mg of iodine. A single administration
orally provides adequate
iodine for about a year, and if given by intramuscular
injection, is satisfactory for about three years. Iodized
oil is most
the iodine deficiency
is severe, when immediate correction is important,
and when iodized salt is
not yet available.
Drinking water is another occasional vehicle for iodine
nutrition. Some systems slowly release iodine from
a porous basket (containing
solution) into well water. Another approach adds
an iodine solution to water in a well or flowing through
A simpler version
drops of a concentrated solution manually to vessels
containing drinking water in
a school or home. If iodine (I2) is added, it can
also sterilize the water; this property is useful because
many regions with
have contaminated food and water.
Occasionally, iodine is given as tablets of potassium
iodide, from 100 to 300 mcg per day or about 1
mg per week. Some
use contain 150 mcg iodine, the recommended amount.
Other vehicles like sugar, bread, and tea have
been occasionally used for iodine delivery. However,
of iodized salt make
favorite for most countries.
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10. What is being done internationally about
iodine deficiency? - The International Council for the
Control of Iodine
(ICCIDD) came into
existence in 1985 with the single purpose of
achieving optimal iodine nutrition worldwide.
It has worked closely with UNICEF and the World
Health Organization towards this objective. These
early efforts led
to a pledge by the
World Summit for Children, in 1990, to achieve
the virtual elimination of iodine
deficiency. A massive effort has taken place
during the past decade. Key players have included governments
WHO, ICCIDD, and the Micronutrient Initiative,
with major funding from Kiwanis International,
of Canada, Australia, the
Netherlands, and the United States, and many
others. Universal salt iodization is the main
strategy. Currently, about 70% of households
worldwide consume iodized salt. Some countries with previously
virtually sufficient; e.g., China, Nigeria, Congo,
Iran, Peru, Ecuador, and Thailand.
This success involves not only the implementation
of iodized salt, but effective national programs,
development of national IDD
coordinating groups, extensive
education at all levels, and monitoring. The
is now on iodine nutrition in those parts of
the world that are still
in Central Asia and Africa, and on maintaining
the progress made in other
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11. How can
countries maintain optimal iodine nutrition? - In
areas with previous iodine deficiency, the key point is monitoring, both
levels in people
(by urinary iodine) and in salt. It is recommended that countries have
regular monitoring by urinary iodine in representative subgroups of the
every several years, with mandatory publication of the information, and
prompt corrective action when deviations occur. Regular quality control
of the iodine
levels in salt, when that is the vehicle, is also essential. Some part
of the government - usually the Ministry of Health or a national coordinating
- needs to take responsibility and be provided adequate resources for
the program. Everyone involved - citizens, government, salt producers, agencies,
sector - needs to be aware, so an active education campaign is a key
of a successful program.
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How can we find out more? - ICCIDD's website (www.iccidd.org) offers
data on the iodine nutrition in each country, and also information about
general, including technical information. ICCIDD has Regional Coordinators
and representatives in many countries who can help. UNICEF and WHO have
nutrition experts in countries and at their central offices. For more
details on thyroid
disease, including iodine deficiency, an excellent online textbook can
be found at www.thyroidmanager.org. If you have additional questions,
ICCIDD through its Regional Coordinators (see "about ICCIDD" on the
website menu), officers, or the Executive Director at email@example.com, or
one of the other partners (UNICEF, WHO, Micronutrient Initiative, Kiwanis International).
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