A cohort of children prenatally exposed to the 1945 atomic bombings in Japan revealed harmful effects of ionizing radiation in a variety of measures of cognitive function, including mental retardation. Here we examined cognitive function in the non-affected, now elderly, cohort.

From 2011-2015, using the Cognitive Abilities Screening Instrument and a maternal uterine radiation dose estimated with the 2002 dosimetry system, we evaluated 303 prenatally exposed subjects and their non-exposed controls from the Adult Health Study of the Radiation Effects Research Foundation, excluding those who had shown marked cognitive effects earlier. About 11% of the subjects were exposed to more than 250 mGy. We examined a self-reported disease history and, using regression analysis, evaluated the relationship between cognitive function and radiation exposures, adjusting for demographic factors.

None of the subjects reported a history of dementia. We also did not find a significant radiation effect on cognitive function overall or in any gestational-week group. Education was associated with a significant effect, but educational level was not associated with radiation dose.

We found no significant radiation effect on cognitive function among 65- to 70-year-old subjects who were prenatally exposed to the bombings and did not have marked childhood cognitive function deterioration. The limitations of this study include a small sample size and potential bias pertaining to non-participation in the Adult Health Study or refusal of Cognitive Abilities Screening Instrument evaluation. Further investigations using various endpoints in other populations prenatally exposed to radiation are warranted.