Dr. Tsubokura's Radiation Lecture Vol.103

Author: Masaharu Tsubokura

Editors: Akihiko Ozaki M.D., Yuki Senoo

105. Getting a sufficient amount of iodine from food

Among all the nuclear accidents that have occurred in the past, the Fukushima Daiichi nuclear power plant accident and the Chernobyl disaster in 1986 are the only nuclear accidents classified as level 7 accidents according to the International Nuclear Events Scale. Although these two events received the same rating, their circumstances and subsequent countermeasures differed. For example, in Fukushima, internal thyroid gland exposure to radioactive iodine was about two orders of magnitude lower compared to after the Chernobyl disaster.

 Another major difference between the two accidents in terms of thyroid gland radiation exposure arose from the difference in people’s daily intake of normal (non-radioactive) iodine from their diets in these two regions. Iodine is an essential element for the production of thyroid hormone. More importantly, it also prevents the thyroid gland from absorbing radioactive iodine.

 Generally, seafood is rich in normal iodine. For example, 1 to 2 grams of kelp tsukudani, a traditional Japanese dish made of kelp simmered with soy sauce and mirin, contains the recommended daily intake of iodine for an adult. In fact, it is rather difficult to avoid iodine in the Japanese diet, which includes a great deal of seaweed.

 On the other hand, residents living near the Chernobyl nuclear power plant, which was located in a non-coastal region, were reported to have iodine deficiency. Therefore, they were extremely vulnerable to radioactive iodine exposure. Therefore, following the Chernobyl disaster, iodine salts were provided to the residents living near the nuclear power plant as a countermeasure against iodine deficiency.

106. People in different age groups developed thyroid cancer in Fukushima and Chernobyl

Among all the nuclear accidents that have occurred in the past, the Fukushima Daiichi nuclear power plant accident and the Chernobyl disaster in 1986 are the only nuclear accidents classified as level 7 accidents according to the International Nuclear Events Scale. Although these two events received the same rating, their circumstances and subsequent countermeasures differed.

 The level of internal thyroid gland exposure to radioactive iodine was about two orders of magnitude lower in Fukushima than at the time of the Chernobyl disaster. The fact that Japanese people generally have a high daily intake of normal (non-radioactive) iodine from their diet also contributed to this difference, as it prevented their thyroid glands from absorbing radioactive iodine. Following the nuclear accidents in Fukushima and Chernobyl, a population-wide ultrasound thyroid gland examination was conducted. A comparative analysis of the results revealed that people in different age groups at the time of examination were diagnosed with thyroid cancer between after the Chernobyl disaster and the Fukushima nuclear accidents.

 In general, younger people are prone to develop thyroid cancer after radiation exposure. In Chernobyl, thyroid cancer was found more often in people who were young at the time of the accident. However, the results of an investigation following the Fukushima nuclear disaster differed; the incidence of thyroid cancer among young people was much smaller compared to among the elderly. This trend of cancer incidence is similar to the incidence of thyroid cancer caused by non-radiational factors. This is one reason the radiation exposure caused by the nuclear accident is unlikely to have increased the incidence of thyroid cancer in Fukushima prefecture.

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The Japanese version of the manuscript was originally published in Fukushima Minyu, a local newspaper in Fukushima prefecture, Japan, 16th and 23th December 2018 was reproduced for MRIC Global under the author's permission.

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