Introduction

Although there is an increasing number of studies that have investigated the association between adverse childhood experiences (ACEs, such as long-term financial difficulties, parental divorce and fear of a family member), unhealthy behaviours (eg, obesity, alcohol consumption, smoking and lower levels of physical activity), adult diseases (eg, cardiovascular disease, diabetes, stroke, cancer and depression) and even early death,1–4 few studies have investigated whether ACEs has an impact on the health of older adults. Because of the rising number of older adults in the world, it is therefore necessary to elucidate the risk factors for diseases among older people.

Further, to address the impact of ACEs on health of older people, it is also crucial to elucidate the commonality of the association because the pathways linking childhood adversities with adult health are likely to be dependent on cultural or social environments.5–7 Therefore, a comparison of countries with different cultural and/or social environments in childhood, but with similar welfare state regimes, may provide further understanding of the underlying mechanisms of ACEs and older adult health. According to a systematic review, most of the recent studies evaluating the impact of multiple ACEs on health were performed in the USA and the UK, with only a few studies conducted in other countries8 such as Asia9 or Nordic countries.10 11 Since the USA and the UK are developed countries with high inequality, there is a need to confirm the association in developed but relatively equal, egalitarian countries such as Japan or Finland.

Japan (population: approximately 127 million) and Finland (population: approximately 5.5 million) are members of the Organization for Economic Co-operation and Development (OECD). The two countries employ a universal healthcare system12 13 and provide free education to those aged 6–15 years.14 According to the World Happiness Report, the level of social support received (measured by having someone to count on in trouble) is relatively high in both countries (92.3% and 94.8% in Japan and Finland in 2015, respectively).15 However, the two countries differ in terms of equality (eg, the Gini coefficient, a measure that represents the income distribution of a country’s residents,16 was 0.38 in Japan in 2014 and 0.26 in Finland in 2015). Out of the 37 OECD countries, Japan ranked 22th and Finland ranked 7th in 2015 in terms of equality.17 Furthermore, immigration policies in the two countries were different at the time of this study; international migrants made up 1.3% of the total Japanese population, whereas 6.2% of the Finnish population were international migrants in 2017.18 Moreover, the divorce rate in Japan in 2017 was 1.7/1000 people,19 whereas it was 2.5/1000 people in Finland in 2015.20 Finally, the prevalence of ACEs also differed between Japan and Finland, with 37% of participants (mean age of 73 years old) in a Japanese study reporting at least one ACE21 and 61% of participants (mean age of 48 years old) in a Finnish study reporting at least one ACE.22 Corporal punishment is not forbidden in Japan, but in Finland it has been prohibited by law since 1983. In summary, both Japan and Finland are developed and egalitarian countries, but their differences in terms of inequality, immigration percentage, divorce rate or policy on corporal punishment might contribute to the differential impact of ACEs on diseases in older adults. For example, de-etiolated social capital due to inequality23 might contribute to stronger impact of ACEs on health in older adults.

Therefore, the purpose of this study was to examine and compare the association between ACEs and adult diseases, including unhealthy behaviours such as smoking, in older adults in Japan and Finland.

Methods

Results

Table 1 shows the distribution of the variables for each country. The prevalence rates of parental divorce, fear of a family member and childhood poverty were 3%, 9% and 47%, respectively, in Japan. In Finland, these proportions were 9%, 13% and 29%, respectively. Of the respondents, 50% of those in Japan and 37% of those in Finland reported having experienced at least one ACE. The mean age of the participants and the proportion of men were higher in Japan than in Finland.

As for SRH, the rate of ‘poor or fair’ was higher in Finland than in Japan (37% and 14%, respectively). The prevalence of cancer was similar in both countries; however, the prevalence of heart disease or stroke and diabetes mellitus was higher in Japan. As for BMI, the mean BMI was higher in Finland than in Japan. The distribution of smoking status was similar. In the case of socioeconomic status, 50% of the people in Finland and 24% of those in Japan were educated for 12 years or more. Of the participants in Finland, 70% were currently working, whereas 66% of those in Japan were currently not working.

Table 2 shows the association between ACEs and SRH and diseases (eg, cancer, heart disease or stroke and diabetes mellitus). For both countries, SRH was associated with each type of ACE and the number of ACEs Interestingly, the point estimates were similar. For example, the OR of the number of ACEs for poor/fair SRH was 1.35 (95% CI 1.25 to 1.46) in Japan and 1.34 (95% CI 1.27 to 1.41) in Finland, after adjusting the covariates (model 2). The ORs of the number of ACEs for cancer, heart disease or stroke and diabetes mellitus were also similar in both studies in model 2. As for each ACE, fear of a family member showed significant risk for cancer and diabetes in Finland, which was not observed in Japan.

Table 3 shows the associations between ACEs and smoking. Former smoking and current smoking were positively associated with the number of ACEs for both counties, and the ORs were similar. Table 4 shows the association between ACEs and BMI. BMI was positively associated with each type of ACE and with the number of ACEs in Finland. This positive association was also significant in Japan.

Discussion

To our knowledge, this is the first study that compares the impact of ACEs on health of older adults between two countries. This study showed that elderly individuals in Japan and Finland who had experienced ACEs had worse health profiles (suboptimal SRH and presence of chronic diseases) and more often had biological and behavioural risk factors (high BMI and smoking) than those with no ACEs. The strength of these associations was weak or modest, and similar between the two countries, although careful interpretation is needed because the assessment of ACEs in Japan and Finland was different. The only exception was BMI that showed a more robust association in the Finnish cohorts than in the Japanese cohort.

Our finding that highlights the association between ACEs and poor health among older adults is consistent with those of other studies. The association was weaker compared with those in other studies5–8 and this might be due to survival bias as we focused on older adults. Regarding SRH, the association between fear of a family member in childhood (ie, in Japan, it was assessed as witness of intimate partner violence) and poor SRH among older adults was slightly stronger than that for parental divorce or childhood poverty in Japan; however, in Finland, such a difference was not observed. Considering that the prevalence of intimate partner violence in Japan was 0.1%, while 0.25% in Finland in the OECD report,32 this result can be interpreted as the detection of intimate partner violence may not be as adequate in Japan compared with Finland, and thus the problem might be unresolved and showed stronger impact for SRH in older age. Alternatively, physical punishment might be more pervasive in Japan than in Finland33; physical punishment is forbidden by law in Finland but not in Japan. Regarding cancer, childhood poverty was associated with cancer among older people in Japan, but this association was not observed in Finland. Childhood poverty in Japan might lead to poverty in older age,29 which may result in delays in medical check-ups or consultations. Previous study has shown that adults with lower health literacy, which is more likely to happen among those living in poverty, are less likely to use healthcare services in Japan.34

Generally, the strength of these associations was similar between the two countries. The consistency of our results in harmonised cohorts from two different countries suggests that childhood adversities affect health similarly in these two societies. In spite of the differences in the cultural and social environments of older adults in these countries,35 36 it is interesting to note that the associations observed were similar. A likely explanation could be the presence of universal healthcare system in these countries which offers adequate medical treatment for diseases over one’s lifespan and is likely lead to the attenuation of the impact of ACEs on health later in life. This might explain the lower OR of ACEs for diseases comparing previous studies, because universal healthcare system might be effective to protect older adults with ACEs. In addition, the presence of equal free educational opportunities in both countries may explain the similar impact of ACEs on adult health, as educational attainment can attenuate the impact of ACEs on later health.37 The presence of high social support,38 cultural engagement, access to trusted adults39 in both countries may also attenuate the impact of ACEs on later-life health through the enhancement of resilience, described as the ability to adapt to adverse environment.40 The effect of ACEs on health, in different educational or healthcare systems, requires further study.

Similarly, ACEs were associated with smoking, which is consistent with the findings of a previous comparative research in eight Eastern European countries5 and other studies in the US,1 41 the UK42 and Finland,43 although this association was weak in the current study. The Eastern European comparative study reported that ACEs were associated with smoking among adults aged 14–66 years.5 The relationship between ACEs and smoking has predominantly been investigated among adults towards middle age; however, few studies have examined these relationships using large community samples of older adults. Our results suggest that ACEs have a consistent long-term effect on smoking among older adults despite the differences in the price of cigarettes or smoking advertisements between the countries. A meta-analysis showed a moderate OR for smoking among those with four or more ACEs compared with those with no ACEs.8 The association was weaker in the current study than that in the meta-analysis, possibly because there were only three ACEs measured in the current study, and the association may have been underestimated because of early death due to smoking and ACEs (eg, survival bias).

ACEs were associated with an increase in BMI in both countries; however, the impact of ACEs was higher in Finland. This association was consistent with that observed in a previous study which showed that ACEs elevated the risk of obesity in the US,1 2 the UK42 and Finland.44 The obesity rate among older individuals was higher in Finland than in Japan in the current study; thus, we used continuous BMI as an outcome. The presence of sampling bias in the current study may have also led to the lower impact of ACEs on BMI in Japan, as the JAGES included only individuals without nursing care.

On the contrary, ‘fear of a family member’ showed significant positive association with cancer and diabetes in Finland, which was not observed in Japan. This might be due to the difference in the assessment of fear of a family member. In the Finnish study, it was asked as it is, while in JAGES, witness of domestic violence was used as a proxy measurement of fear of a family member. It may be possible that in Japan, witness of domestic violence may not always induce fear of a family member, say, if the child was used to it. Thus, in Japan the association was weak. Alternatively, fear of a family member may not necessarily be a risk factor for adult disease in Japan because of the rich social network, especially among kin relatives,45 46 which provides an environment for children to escape from a fearful family member. Further study using the same question is needed to confirm whether the discrepancy is due to the difference in the assessment of social environment.

There are several limitations to this study. First, this was a cross-sectional study conducted among older adults. As ACEs were self-reported, differential recall bias cannot be ruled out. Recent review showed poor agreement between prospective and retrospective assessment of childhood maltreatment.47 However, in contrast, other review studies reported that the validity of retrospective assessment of ACEs is acceptable.48 49 Second, these results, although based on harmonised measures, were derived only from two egalitarian developed countries, which preclude the generalisation of the findings to other countries. Further studies are warranted to investigate the association between other ACEs and adult disease in different cultural settings, and in low-income and middle-income countries. Third, we did not assess other ACEs such as sexual abuse, neglect, childhood neighbourhood deprivation or family disfunction (ie, mental disorder of a family member, or incarcerated family member), and thus the number of ACEs were limited only to three. The limited number of ACEs precluded to assess stronger impact of ACEs on adult diseases, as a previous meta-analysis revealed.8 Further studies are necessary to investigate the impact of other ACEs on the health of older adults. Fourth, there is a disparity in the measurement of ACEs and health, and ACEs and health behaviours, across the JAGES, FPS and HeSSup. The differences in measurement might result in heterogeneity of the results. More specifically, the assessment of fear of a family member in the JAGES, FPS and HeSSup was different, which may result in heterogeneity between study estimates. Fifth, the participants in the JAGES did not have functional disability, and hence might be healthier than the average Japanese older population. Therefore, the results of the study might be underestimated. Alternatively, the results might be subjected to survival bias. The average age of the study participants was 69.5 years in Japan and 64.4 years in Finland. People who passed away from ACE-related diseases or health risk behaviours before the current study would not have been included in the current study. Therefore, the results of the current study may underestimate the health effects of ACEs. Further, FPS was a not representative sample, and thus the prevalence of diseases, such as cancer, may be different from other studies. Sixth, considering other covariates such as levels of inequality, current and previous household income, environmental risks (eg, parental smoking) or genetic variation was not feasible due to data availability. In fact, education level was higher in the Finnish sample than in the Japanese sample. Finally, we were unable to pool the data of the two countries due to restriction on the Finnish data, and therefore interactive effects of the countries and ACE on adult health were unclear.

Nonetheless, this is the first study that investigated the association between ACEs and health and health behaviour among older people in two countries. In Japan and Finland, the relationship between ACEs and health was similar for SRH, specific diseases and smoking. The impact of ACEs on BMI was stronger in Finland than in Japan. These results suggest a notable association between ACEs and health among older people, and that this association remains consistent even in countries with a different social environment. Based on these findings, health policy to address ACEs is needed to prevent future diseases among older adults.