Thyroid Detection Rate Clarified Following Fukushima Power Plant Accident

Researchers in Japan have for the first time clarified the thyroid cancer detection rate in children and adolescents following the Fukushima Nuclear Power Plant disaster in March 2011, according to a study recently published in The Journal of Clinical Endocrinology & Metabolism.

The team, led by Hiroki Shimura, MD, PhD, of Fukushima Medical University, points out that thyroid cancer is of great concern in Fukushima Prefecture, especially since studies have shown the adverse health effects in areas where there is radiation fallout, like Chernobyl, where there was a “substantial rise in thyroid cancer among exposed young people.”

The researchers analyzed data from 294,905 participants, 18 years old and younger when the earthquake hit, from October 2011 to March 2014. These patients had thyroid ultrasound examinations, and then a second confirmatory examination was performed on 2,032 patients. “Thyroid cysts, nodules, and cytologically suspected cancers were detected in 68,009, 1,415, and 38 subjects in males and 73,014, 2455, and 74 subjects in females, respectively,” the authors write. “There was an age-dependent increase in the detection rate of thyroid nodules and cancer, but that of cysts reached a peak at 11–12 years. Sex affected the prevalence of thyroid nodules and cancers after the onset of puberty, but only a small difference was exhibited in that of cysts.”

Detection rates of thyroid cysts and nodules were higher in females than males, which follows the same patterns reported in previous studies, the authors note. They also write that the present study showed an evident gender difference in the detection rate of nodules 10 years or older. “That the age of 10 years in females almost coincides with the onset of puberty suggests that the gender difference during puberty might be induced by estrogen-dependent stimulation of thyroid cell proliferation,” the authors write.

This study did have some limitations. The Japanese diet and environment may not be comparable to the Russian diet and environment, for example. Japanese people consume more iodine in seaweed.

Previous studies have shown that there may be a latency period of four to five years for developing radiation-induced thyroid cancer. The fact that the examination period in this study was within three years after the nuclear accident reasonably suggested that this study was performed before any radiation-induced influence. Therefore, the results demonstrated in this study will confer as reference data to future epidemiological studies of nodular thyroid diseases in children, adolescents, and young adults.

“In conclusion,” the authors write, “the accurate prevalence of the findings of thyroid abnormalities and information on age-dependence in neonates to adolescents has been, for the first time, clarified in Fukushima, following the introduction of a new highly-sophisticated methodology that can easily detect quite small and asymptomatic thyroid abnormalities.” They also write that the results of this study will contribute to future epidemiological studies on thyroid diseases in children and adolescents.