Association between radiation dose, thyroid hormone, and IQ levels in children exposed to radiation in utero after the Chernobyl accident

Abstract

Few studies have explored the effects of n utero radiation exposure on human health and cognition and none have taken into account thyroid hormone levels (T3), which have shown to affect cognitive performance. We investigated mechanisms of possible radiation effects on IQ in two cohorts of 250 persons each: exposed n utero after the Chernobyl accident: a ‘higher exposure group (HEG)’, whose mothers resided in more heavily contaminated territories at the time of the Chernobyl accident, and a ‘lesser exposure group (LEG)’ whose mothers resided in less contaminated areas. The dataset included information on estimated prenatal thyroid radiation dose, gestation week at the time of the accident (ATA); thyroid hormones: T3 (triiodothyronine) and T4 (thyroxine) levels measured at age 11–12 years and general IQ measured at three time points: t1: 6–7 years old; t2: 11–12 years old and t3: 15–16 years old. Descriptive and inference analyses were used to explore the dynamic of changes through time and the associations between key variables at the three time points. Estimated radiation doses to the thyroid gland were substantially higher in the HEG than in the LEG (mean 391 vs 25 mGy respectively). Significant differences in thyroid hormones levels were observed between the two groups, with lower values in T3 (higher in T4) in the LEG. At t1, the general IQ, as well as verbal and non-verbal IQ scores, were lower in the HEG than in the LEG. In the HEG, analyses adjusting simultaneously for radiation dose, gestational week ATA and T3 levels suggest that all three variables are associated with IQ, with the latter being highest among those exposed later during gestation and decreasing with increasing level of dose and of T3. No significant association was observed between IQ and T4 levels. No effect of exposure on IQ was seen in the LEG. Further investigation of this hypothesis will be important to understand the relation between n utero exposure radiation dose to thyroid, thyroid hormone levels and IQ, taking into account effects of potential confounding factors (physiological stress, maternal anxiety related evacuation).

HIGHLIGHTS

1. We followed up persons exposed in utero to radiation from the Chernobyl accident

2. Among the most highly exposed, IQ was higher among those exposed later during gestation

3. Among the most highly exposed, IQ also decreased with increasing level of dose and of T3

4. No such relation was seen in those with lower exposure

5. Our study provides insights into the possible relation between prenatal radiation dose and IQ and the factors which may modify it

Keywords:

• In utero exposure
• thyroid doses
• Chernobyl accident
• thyroid hormones
• IQ

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The author(s) reported there is no funding associated with the work featured in this article.

Notes on contributors

Liudmila Liutsko

Liudmila Liutsko, PhD., MSc. Currently work at the Catalonian Institute of Health (ICS in Spanish) and IDIAP Jordi Gol (affiliated to ICS). Recently she is also involved in the research work of the GRASSIR (Research Group on Sexual and Reproductive Healthcare in Catalonia). Previously 6 years of work as a post-docs and co-PI at ISGlobal (Radiation Programme), Spain. She is a mentee-member of ICRP TG121.

Sergey Igumnov

Sergey Igumnov, M.D., Dr.Sci (Psychiatry and Radiobiology) work at the Republican Scientific and Practical Center for Mental Health (Deputy Director for Science), Minsk, Belarus.

Vladimir Drozdovitch

Vladimir Drozdovitch, PhD., is a Staff Scientist at National Cancer Institute (USA), who has worked at the field of post-Chernobyl radiation dosimetry for 35 years.

Elisabeth Cardis

Elisabeth Cardis, PhD., Prof. is Professor of Radiation Epidemiology and Head of the Radiation Program at ISGlobal (previously the Center for Research in Environmental Epidemiology) in Barcelona since 2008. Before that, she led the Radiation Group at the International Center for Cancer Research (IARC) of the WHO in Lyon, where she worked for over 20 years. She earned a PhD in Biostatistics from the School of Public Health at the University of Washington (Seattle, USA) in 1985 and was visiting scientist at the Radiation Effects research Foundation in Hiroshima Japan in 1981–1982. She is the author of over 250 peer-reviewed publications and has extensive experience in epidemiological studies on health effects of medical, accidental, environmental and occupational exposures to radiation (ionizing and non-ionizing); in radiation protection; in the characterization and modeling of uncertainties in exposure estimates and in health impact assessment. She has supervised numerous PhD theses and numerous post-doctoral fellows and has been examiner for PhD theses in several European countries.