Radioactive iodine was supposed to be the cause of thyroid cancer after the Chernobyl nuclear power plant accident in 1986, which resulted in a sudden increase in childhood thyroid cancer. Radioactive iodine accumulates in the thyroid gland when it enters the body through respiration or with food, exposes the cells from inside the thyroid gland, and causes cancer.

Fukushima Prefecture has regularly examined the thyroid glands of children who were 18 and under at the time of the accident at the Fukushima Daiichi nuclear power plant. 252 of these people have been diagnosed with thyroid cancer or suspected of having thyroid cancer, and of these, 202 have been confirmed to have cancer through surgery (according to data released by January 15, 2021). The Fukushima Prefectural Health Study Review Committee concluded that “the number of thyroid cancers found is in the order of dozens of times higher than the prevalence estimated from thyroid cancer incidence statistics and other sources” ” while at the same time expressing the view that “it is difficult to determine the correlation with the nuclear accident.