RERF Report No. 11-14

Paper published in Journal of the Neurological Sciences §“Trajectories of Cognitive Function in Dementia-free Subjects: A RERF Adult
Health Study”
Michiko Yamada, Reid D. Landes, Yasuyo Mimori, Yoshito Nagano, Hideo Sasaki
J Neurol Sci 2015 (April); 351(1-2):115-9(doi: 10.1016/j.jns.2015.02.050)

Study Findings
Age is an important predictor of cognitive function. In the elderly subjects in our study, we
found cognitive function level to be low and the degree of cognitive decline to increase rapidly
with aging. Years of education affected cognitive function level but not the degree ofage-associated cognitive decline. The effect of sex on cognitive function was insignificant. The
higher cognitive function scores noted in the younger cohorts and men are attributable to more
years of education in these groups.
Explanation
The effects of age, sex, education, and birth cohort on cognitive function were analyzed ina population of people who did not develop dementia during cognitive function monitoring from1992 to 2011.
1. Objectives
The objectives were to investigate the relationship of age, sex, education, and birth cohort
to cognitive function level and age-associated changes in cognitive function in a population thatwould most likely not progress to dementia (i.e., population not developing dementia during
monitoring).
2. Methods
We followed the cognitive function of the 1538 Hiroshima participants in the RERF Adult
Health Study who were 60 to 80 years of age in 1992 and did not develop dementia during
monitoring through 2011. A standardized cognitive performance test, the Cognitive Ability
Screening Instrument (CASI), was used to evaluate cognitive function. The data were analyzed
with mixed-effects models.

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3. Results(1) Cognitive function level was higher in the younger subjects and those with more education
than in the older subjects and those with less education. The effect of sex was insignificant
on cognition.
(2) The degree of cognitive decline increased with age. Sex and education did not modify thedegree of cognitive decline with age.
(3) The higher cognitive function seen in the younger cohorts and men is attributable togreater education in these groups.
We found that age at examination and education affected cognitive function level and thatage affected changes over time in cognitive function. These findings suggest the need toconsider age and educational attainment when setting cognitive function cutoff values fordementia screening (i.e., values below which the person screened is considered to havecognitive decline). The findings also indicate that knowledge about the normal degrees ofchange in cognitive function in dementia-free people of a given age group will assist the early
identification of dementia in people of that age group.
The Radiation Effects Research Foundation has studied A-bomb survivors and their offspring inHiroshima and Nagasaki for more than 60 years. RERF’s research achievements are considered theprincipal scientific basis for radiation risk assessment by the United Nations Scientific Committee on theEffects of Atomic Radiation (UNSCEAR) and for recommendations regarding radiation protection
standards by the International Commission on Radiological Protection (ICRP). RERF expresses its
profound gratitude to the A-bomb survivors and survivors’ offspring for their cooperation in our studies.

§Journal of the Neurological Sciences provides a medium for the prompt publication of original articles

in neurology and neuroscience from around the world. JNS places special emphasis on articles thatprovide guidance to clinicians around the world, report cutting-edge science related to neurology, educate
readers about relevant and practical clinical outcomes in neurology, and summarize or editorialize thecurrent state of the literature. (Impact factor in 2014: 2.262)

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