Radiation Health Effects

Thus far, no significant effects of radiation from the nuclear accident have been confirmed in either the Thyroid Ultrasound Examination program or the Pregnancy and Birth Survey.

Thyroid Ultrasound Examination (TUE) (Consensus of the Fukushima Prefectural Oversight Committee)

Preliminary Baseline Survey (PBLS) (first-round survey)

It can be concluded that thyroid cancers found thus far through the Thyroid Ultrasound Examination (TUE) program are not attributable to radiation released by the Fukushima accident.

Major reasons for this conclusion:
  • Exposure doses due to the accident at Fukushima Daiichi were generally lower than those of the Chernobyl accident.
  • The period of time (one to four years) from exposure is too short for the usual evolution of radiation-related thyroid cancers.
  • Cancers have not been detected in those who were age five or younger at the time of the accident.
  • There are no substantial regional differences in detection rates.

Source: March 2016 Fukushima Prefectural Oversight Committee

The second-round survey

The Fukushima Prefectural Oversight Committee concludes that, at present, no causal relationship can be identified between radiation exposure and thyroid cancers detected during the Full Scale Survey (FSS) (second-round survey).

Major reasons for this conclusion:
  • Analysis of estimated thyroid absorbed doses published by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) and corresponding detection rates of thyroid cancer shows no consistent dose-effect relationship.
  • The detection rates of actual or suspected thyroid cancer (grade B ultrasound findings, malignancy, or suspicion of malignancy needing confirmatory examination) was higher in older age groups at the time of the accident, in contrast to thyroid cancers frequently detected after the Chernobyl accident, which were mainly in younger children.

Source: The 36th Fukushima Prefectural Oversight Committee, October, 2019

From the first-round survey to the fourth-round-survey

Comprehensive data analysis supports the conclusion that “no association between thyroid cancer and radiation exposure has been observed.”

The major reason for this conclusion:
  • No statistical significance has emerged to link thyroid cancer detection rates with radiation dose estimates based on geographical region or individual circumstances.

Source: The 21st Thyroid Examination Evaluation Subcommittee, July 2023 (Document #4)

The results of the Pregnancy and Birth Survey (PBS)

Preterm births, low birth weights, and congenital anomalies have been consistent with national government statistics and commonly reported data in general.

Source: The 44th Fukushima Prefectural Oversight Committee, May, 2022 / Guidelines for Obstetrics practice 2023

Preterm births rate, Low birth weight rate, and Congenital anomalies Rate

Preterm births rate Low birth weight rate Congenital anomalies Rate
FY2011 4.6 (5.7) 8.6 (9.6) 2.85 (2~3)*
FY2012 5.6 (5.7) 9.2 (9.6) 2.39
FY2013 5.2 (5.8) 9.6 (9.6) 2.35
FY2014 5.3 (5.7) 9.8 (9.5) 2.30
FY2015 5.6 (5.6) 9.4 (9.5) 2.24
FY2016 5.3 (5.6) 9.2 (9.4) 2.55
FY2017 5.3 (5.7) 9.2 (9.4) 2.38
FY2018 5.2 (5.6) 9.0 (9.4) 2.19
FY2019 5.1 (5.6) 9.1 (9.4) 2.71
FY2020 4.4 (5.5) 8.1 (9.2) 2.21

Figures in the brackets are the proportion of preterm deliveries and incidence of low birth weight infants reported in Vital Statistics published by the Ministry of Health, Labour and Welfare for the same fiscal year.
*Figures in the brackets are generally reported incidence in the Guidelines for Obstetrics practice (2023)