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Radiation and Children Section 4: Iodine 131 and Thyroid Cancer in Children


Keywords: DNA, iodine 131, health, nuclear, children, radiation, reactive oxygen, thyroid, Toshiya Inaba, genes

This section explains the troubling connection between iodine 131 and thyroid cancer in children. Reading the first three sections will provide an introduction to the subject.

The thyroid and thyroid cancer

First, let?s go over some basic facts about the thyroid. Located in the front of the throat, just below the skin, the thyroid is a gland that produces thyroid hormones. Thyroid hormones are the source of our energy and activity, and without sufficient production, we feel less energetic, and in the case of children, development is delayed. On the other hand, excess production makes us overactive, causing a whole host of other symptoms. Thyroid hormones are distinguished by their iodine content. Iodine is found only in small amounts in food, so the thyroid serves as an iodine tank where iodine can be stored on a regularly basis.

Thyroid cancer among children is very rare, with only a few cases per year in Japan. In most cases, treatment is successful and the children survive the disease.

What is iodine 131?

Iodine found in the natural environment is called iodine 127. On the other hand, iodine 131 is rarely found in the natural world, but exists in large amounts in nuclear reactors. Iodine 131 is radioactive and changes to a substance called xenon. Because the thyroid is unable to distinguish between iodine 127 and iodine 131, both are absorbed and accumulated in the thyroid.

Chernobyl Nuclear Accident

When it comes to the subject of iodine 131 and thyroid cancer in children, it is necessary to discuss the 1986 Chernobyl nuclear disaster in Ukraine. It was this accident that underscored the correlation between nuclear accidents and the high incidence of thyroid cancer. At the time, Ukraine was part of the former Soviet Union, whose secretive system of government led to a larger scope of the damage and problems with the unreliability of basic data. For this reason, some of the following information may not seem hard to understand.

In the accident, a fire and explosion released extremely large levels of iodine 131 into the atmosphere. The released iodine 131 contaminated much of the surrounding region and fields. People who drank milk from dairy cows that had grazed in these contaminated fields are thought to have ingested iodine 131. This iodine 131 was absorbed by the thyroid, which then caused cancer.

We do not know the exact number of children with thyroid cancer. There are said to be between several hundred to several thousand patients, an increase that can be anywhere between 50 to 60 to over 100 times greater than before the accident. At the time of the accident, approximately half of all the patients were children aged five years and under, but it is of great concern that we do not know the amount of iodine 131 absorbed by these children and there is no reliable data exists. Fortunately, thyroid cancer is amenable to treatment and treatment of thyroid cancer in the wake of the Chernobyl accident is also considered to be successful.

Chernobyl and Fukushima Nuclear Accidents: Similarities and Differences

In both accidents, iodine 131 was released into the air. Thereafter, they both followed the same general course by entering and polluting the water supply, vegetables, and milk through the earth. In the case of Fukushima, it was reported that it had flowed into the sea and polluted fish which may have made readers worry that the situation was far more severe.

Looking closely at these two incidents, however, there are differences, the largest being the amount of released iodine 131. This series has repeatedly emphasized that the ?quantity? of radiation or radioactivity is important. A great amount of radiation was released at Chernobyl, and it is said to have been several hundred times greater than that released by the atomic bomb that was dropped on Hiroshima. Unfortunately, we do not know how much iodine 131 the children absorbed, but we can suppose it was a large amount.

On the other hand, in the Fukushima accident, the level of iodine 131 was monitored immediately after the accident. When the levels in the thyroids of children near the Fukushima nuclear plant were checked for radiation with a survey meter, all were found to be below the standard value (permitted value). As explained earlier in Section 3, the method of determining the permitted value is extremely difficult. The permitted level is set at such an extremely low that it is hard to imagine that even a level slightly higher would lead directly to an increase in thyroid cancer.

Another major difference between the two accidents is that Chernobyl is a landlocked town with little iodine. Goiter or a swelling in the thyroid gland, which is caused by iodine deficiency, is rare in Japan, but is common in the Chernobyl region. When the thyroid is deficient in iodine, it attempts to compensate by the absorbing more iodine 131.

In fact, iodine 131 is not just found in nuclear reactors, but also used widely in hospitals. Iodine 131 is also taken by patients to both test and treat thyroid disorders. Despite this, it has never been known to be carcinogenic.

Do not get too anxious about it

For these reasons, I think that there is little possibility that thyroid cancer in children will increase because of the Fukushima Nuclear Accident. Of course, we will have to carry out thorough follow-up surveys, but I would like to ask parents not to become overly anxious about this.

The original report was posted on the CRN Japanese site in April 2011.


Toshiya Inaba
Professor and Vice Director of Hiroshima University Research Institute for Radiation Biology and Medicine, Doctor of Medicine.
Graduated from Tokyo University Medical School. After employment at Saitama Children’s Medical Center, St. Jude Children’s Research Hospital, Jichi Medical University School of Medicine, appointed Professor, Hiroshima University Research Institute for Radiation Biology and Medicine in 2001, and Vice-Director since 2009. Specializes in hematology (mechanism of the onset of leukemia, pediatric hematology), microbiology, and radiation biology.
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