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日本における放射線、母乳栄養_Q&A: Japan, radiation and breastfeeding

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2011年03月24日(Thu) 18:39

ICCIDDという世界でヨード欠乏症対策を行っている、
団体からの情報です。

適宜、和訳をつけていきます。

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Iodine and Japan Nuclear Accident

Q&A: Japan, radiation and breastfeeding

International Council for the Control of Iodine Deficiency Disorders
Statement for Publication March 19, 2011

On March 11th Japan experienced a devastating earthquake followed by a tsunami
resulting in catastrophic damage and loss of life. This natural disaster in turn
caused a manmade disaster by severely damaging four nuclear reactors with
the ongoing release of radioactivity. Of particular concern is iodine (I)-131,
the unstable, radioactive isotope of iodine. Normally, stable iodine is
an essential element for the thyroid gland to produce thyroid hormone that
is required for the optimal development of the human brain. As a result, brain
damage from iodine deficiency in the fetus and developing child is the leading
cause of preventable mental retardation.

The requirement for iodine in adults and children is about 150 micrograms a day,
 usually in the form of iodized salt. Pregnant and breastfeeding women require
more iodine; the minimum amount for them being 250 micrograms a day. My organization,
ICCIDD, along with UNICEF, WHO and other agencies have been strong advocates of
the use of iodized salt. Significant iodine deficiency occurs in about 2 billion
people or one- third of the global population. As an example of the importance of
this micronutrient, administration of iodine to population living in areas of
moderate to severe iodine deficiency results in an average increase of 10 to 13
points in their IQ.

When a nuclear reactor malfunctions, enormous amounts of the radioactive isotope of
iodine (I-131) is released into the atmosphere and will be deposited on crops and
pastures and can then enter the food chain mainly, but not exclusively, through milk.
When taken up by the human thyroid, the I-131 itself produces radiation that
damages the gland and strongly increases the risk of developing thyroid cancer.
The risk for thyroid cancer is greatest in children. The administration of a large
stable iodine dose of 130 milligrams (mg) which is one thousand times the normal
 intake dilutes the I-131 and limits accumulation of the radioactive isotope
in the thyroid. Iodine in the form of potassium iodide (KI) administered within
1-2 hours after internal contamination with I-131 can block more than 90% of
the thyroid uptake. Taking KI more than 4 hours after the event provides little
protection. In an iodine-sufficient population, the acute administration of iodized
salt has little or no beneficial effect. However the presence of iodine deficiency
increases the amount of radioactivity taken up by the thyroid. ICCIDD recommends
adherence to the recommendations provided by the U.S. Center for Disease Control
and Prevention (CDC) http://emergency.cdc.gov/radiation/japan/ki.asp.
Fortunately, the Japanese population has a high intake of iodine, even without
using iodized salt, due to a diet containing iodine-rich substances like seaweed.

ICCIDD recommends the importance of maintaining a normal iodine intake for all
humans that will lessen the uptake of the I-131 radioisotope after a nuclear accident.
Ingestion of excessively large amounts of iodine in the absence of exposure to I-131
 is not helpful and can cause side effects such as underactivity (hypothyroidism)
or overactivity (hyperthyroidism) in people with underlying thyroid disease.


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