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-W. Bradford Wilcox
Associate Professor of Sociology, University of Virginia 

Rough Childhood, Greater Risk of Dementia in Japan

Bryce J. Christensen and Nicole M. King

As the global population ages, due to advances in medicine and other developments leading to longer life expectancies, interest in what leads to a healthier old age is increasing. 

Chief among the concerns older adults might have to face is the onset of dementia, as a team of Japanese researchers highlights in the opening to their new paper studying the relationship between adverse childhood experiences and incidence of dementia in older Japanese adults. “Approximately 47 million people had dementia in 2015 worldwide,” the researchers open, “and this number is expected to triple by 2050.” Research has demonstrated that overall health has a crucial impact on chances of developing dementia, but in a recent model, “education showed the second highest percentage in terms of the contribution to the onset of dementia,” which the researchers believe demonstrates the importance of childhood experiences to the later risk of developing this dreaded disease. 

The researchers speculate that “adverse childhood experiences”—which includes loss of a family member, family psycopathology, and child maltreatment—may play a role in the risk of developing dementia, as previous research has demonstrated that “individuals who experienced adverse childhood experiences showed deficits in brain structure and function.” 

Japan, the researchers continue, is a “unique case” to study the relationship between adverse childhood experience and risk of dementia for two reasons. First, the Japanese are noted for their longevity. Second, older Japanese adults experienced the consequences of being reared amidst (or shortly after) World War II. To conduct their study, the researchers used data from the Japan Gerontological Evaluation Study, a large-scale survey administered to older Japanese adults (over 65 years of age) in 2013. This data was then linked to the incidence of depression by 2016. Survey participants were born between 1915 and 1948. 

Survey respondents answered seven questions detailing what, if any, of these adverse childhood experiences they underwent before the age of 18: “interpersonal loss (parental loss or parental divorce), family psychopathology (parental mental illness or family violence), and abuse and neglect (physical abuse, psychological neglect, or psychological abuse).” The participants were then grouped depending on whether they had experienced 0, 1, 2, or 3 or more of these.  The researchers also took into account a range of covariates, including economic hardship and child height (a proxy for nutrition). 

The researchers report that, “The prevalence of each adverse childhood experience was similar for men and women. The adverse childhood experience with the highest prevalence was parental death (1881 men [23.1%] vs 2048 women [22.1%]), and that with the second highest prevalence was psychological neglect (1182 men [14.5%] vs 939 women [10.1%]).” Divorce was rare, with only 326 participants reporting parental divorce. The researchers also found that “participants who experienced adverse childhood experiences had a lower education level, were more likely to be unmarried, had less social participation, were more likely to have a history of smoking, and were more likely to have depression.”

In the follow-up, dementia was present in 703 participants, and adverse childhood experience did, in fact, have an impact on the risk of developing dementia. Specifically, the more adverse events survey respondents faced in childhood, the greater the risk of developing dementia. So while experiencing parental death alone (the most common risk factor) was not enough by itself to increase the risk of dementia, experiencing parental death along with some form of abuse was associated with increased risk. Interestingly, although the numbers of children who experienced parental divorce were small, these children had a hazard ratio of 1.2-1.29 of developing dementia, while children who experienced parental loss had hazard ratios of 0.96-0.99 (no association). While the researchers fail to comment on this, and it may be partially due to other factors (divorce was rare, and thus perhaps even more stigmatized and traumatic), children who experienced parental divorce actually had a higher risk of developing dementia than those who experienced parental death.

The researchers also report, “We found that participants who experienced adverse childhood experiences had a lower education level, were more likely to be unmarried, had less social participation, were more likely to have a history of smoking, and were more likely to have depression,” and that adult factors like this accounted for 67% of the association between adverse childhood experiences and risk of developing dementia. They also note that those same adverse experiences “can hinder opportunities in terms of receiving education, building social relationships, and developing healthy behaviors, thus increasing the risk of diseases associated with the onset of dementia.” In other words, a large part of the problem is the types of negative psychosocial or socioeconomic impacts that adverse childhood experiences bring throughout the life course. 

In summary, the researchers report that “This study found an association between adverse childhood experiences and late-life dementia onset longitudinally among older adults, using a large-scale population-based sample in Japan.” For pro-family advocates, this study bears an important lesson: Childhood experiences have a crucial impact on the life course, and even on the brain.

(Yukako Tani, Takeo Fujiwara, and Katsunori Kondo, “Association Between Adverse Childhood Experiences and Dementia in Older Japanese Adults,” JAMA Network Open 3.2 [2020]: e1920740.)