Abstract
The impact of the coronavirus disease 2019 (COVID-19) pandemic on dental caries is unknown. We investigated the effect of the pandemic on child dental caries in Japan by comparing the increase in dental caries from fourth to sixth grade between two cohorts, COVID-19 exposed cohort and COVID-19 unexposed cohort, using difference-in-differences analysis. Longitudinal data that followed elementary school children in Adachi City, Tokyo, were analyzed. The analysis consisted of two cohorts: those who were in fourth grade in 2016 and sixth grade in 2018 (COVID-19 unexposed cohort, N = 399) and those who were in fourth grade in 2018 and sixth grade in 2020 (COVID-19 exposed cohort, N = 3,082). Children's dental caries were examined by school dentists. A difference-in-differences analysis, adjusting for time-variant variables, i.e., household socioeconomic status, children's oral health behavior, and caregivers' psychological distress, was performed. In fourth grade, the number of Decayed, Missing, and Filled permanent Teeth (DMFT) was not different between the COVID-19 unexposed and exposed cohorts (mean = 0.241 and 0.242, respectively). In sixth grade, DMFT increased by 0.067 in the COVID-19 unexposed cohort and 0.180 in the COVID-19 exposed cohort. The interaction term of grade and cohorts for caries by difference-in-differences analysis showed that dental caries among the COVID-19 exposed cohort showed a significant increase in the number of dental caries by 0.116 (95% confidence interval 0.015, 0.216) compared to the COVID-19 unexposed cohort. Child dental caries slightly increased after the pandemic. Studies with longer follow-ups are needed to evaluate the impact of the pandemic on child dental caries.
Keywords: Child oral health, COVID-19, Epidemiology
Introduction
Oral diseases are highly prevalent, affecting more than one-in-three, or 3.5 billion, of the global population [Peres et al., 2019]. The World Health Assembly of the World Health Organization has acknowledged the health, social, and economic burden of oral diseases and has approved a resolution on oral health, stating that oral diseases must be prioritized and addressed by integrating them into other noncommunicable disease strategies [World Health Organization, 2021].
Dental caries is the most common disease among children [Global Burden of Disease Collaborative Network, 2020], reducing the quality of life by severe pain and discomfort [Selwitz et al., 2007], and it is also known as an early marker of social disadvantages and subsequent health inequalities [Marcenes et al., 2013; Watt et al., 2018]. As the incidence of dental caries is relatively stable and the burden accumulates throughout life [Broadbent et al., 2013; Heilmann et al., 2015], monitoring and preventing dental caries since childhood is crucial.
The coronavirus disease 2019 (COVID-19) pandemic and policy measures to control its transmission have changed the family environment, a significant determinant of child dental caries [Fisher-Owens et al., 2007]. The economic fallout due to the pandemic has imposed household income loss and increased parental stress and anxiety [Horiuchi et al., 2020; Takaku and Yokoyama, 2021; Westrupp et al., 2021]. School closure has been implemented in many countries and has affected more than 80% of children [Lancker and Parolin, 2020]. In Japan, most schools had been closed from March to May 2020 [Cabinet Office, 2020], and after reopening, staggered attendance and online classes were operated, and the children had to spend a certain amount of time at home. School closure and the encouragement of remote working increased the parental burden for childcare, particularly for mothers working from home [Heggeness, 2020; Yamamura and Tsutsui, 2021], which may have led to a lack of proper childcare. These changes could have affected child dental caries because lower household income, parental stress, and neglectful parenting are known to be the risks of child dental caries [Masterson and Sabbah, 2015; Schwendicke et al., 2015; Matsuyama et al., 2020]. Moreover, the lifestyles of children could have changed to be cariogenic through the pandemic: the sugar consumption of children increased during lockdown due to the COVID-19 pandemic [Pietrobelli et al., 2020]. Despite these backgrounds, no study has investigated the impacts of the COVID-19 pandemic on child dental caries.
Difference-in-differences analysis elucidates the impacts of a particular intervention (e.g., policy reform, disaster, and pandemic), utilizing data that contain treated and control observations before and after the intervention. Under the assumption that the treated and control groups follow the same trajectory of the outcome if there is no intervention (i.e., parallel trend assumption), the difference in changes between the treated and control groups indicates the causal effect of the intervention [Angrist and Pischke, 2008]. Thus, by comparing the increase in dental caries among children before and after the pandemic with another birth cohort that was not affected by the pandemic, the effect of the COVID-19 pandemic on child dental caries is estimable. This study investigated the effect of the COVID-19 pandemic on child dental caries in Japan by comparing the increase in dental caries from fourth to sixth grade between different birth cohorts.
Methods
Study Setting and Participants
The Adachi Child Health Impact of Living Difficulty (A-CHILD) study is a longitudinal study that followed elementary school children in Adachi City, Tokyo [Ochi et al., 2021]. It consists of two types of longitudinal surveys. As a complete-sample survey for children who were first graders in all elementary schools in the city in 2015, the baseline survey was conducted in 2015, and follow-up surveys were conducted in 2016 and every 2 years. On the other hand, a fixed-grade survey, targeting fourth and sixth graders in 9 elementary schools, was conducted every 2 years from 2016. Therefore, two waves of panel data from fourth to sixth grades were available for the following two cohorts: children who participated in the complete-sample survey (fourth grade in 2018 and sixth grade in 2020) and those who participated in the fixed-grade survey (fourth grade in 2016 and sixth grade in 2018). The present study analyzed these data.
In October 2016, the questionnaires were distributed to fourth graders (i.e., 9–10 years old) and their caregivers in nine public elementary schools in Adachi City. These nine schools were selected by municipality officers to represent Adachi City. The follow-up survey was conducted in October 2018 in the sixth grade. Therefore, this cohort did not experience the COVID-19 pandemic (hereafter the COVID-19 unexposed cohort). The 2018 survey was also conducted in fourth graders and their caregivers, the main cohort of the A-CHILD study, which covered all 69 public elementary schools in the city. The follow-up survey was conducted in October 2020 in the sixth grade. Thus, this cohort experienced the COVID-19 pandemic, at least the first and second waves (hereafter the COVID-19 exposed cohort).
Figure 1 shows the flowchart for the present study participants. The survey for the COVID-19 unexposed cohort was completed with informed consent by 534 children and caregivers in the fourth grade (valid response rate: 86.7%), and 449 were followed in the sixth grade (follow-up rate: 84.1%). The survey for the COVID-19 exposed cohort was completed with informed consent by 4,290 children and caregivers in the fourth grade (valid response rate: 80.8%), and 3,733 were followed in the sixth grade (follow-up rate: 87.0%). After excluding children with missing information, the data of 399 children of the COVID-19 unexposed cohort and 3,082 children of the COVID-19 exposed cohort were included in the analysis.
Fig. 1.
Flowchart of the study participants. COVID-19, coronavirus disease 2019.
Measurements
Dental caries in children were evaluated by school dentists at the school health checkup. In Japan, mandated school health checkups, including dental examinations, are conducted annually. While schools are generally required to complete school health checkups by the end of June, the health checkup for the COVID-19 exposed cohort in the sixth grade was allowed to be delayed till March 2021 (i.e., the end of the Japanese school year 2020) due to the COVID-19 pandemic. As the school health checkup was conducted nationwide, the dentists were not calibrated because of a feasibility issue; they were required to follow the national guideline instead [Japan Society of School Health, 2015]. A dental mirror and ball-ended probe or the community periodontal index probe were used under sufficient light in schools, and dental units or radiography was not employed. The present study utilized the data on the number of Decayed, Missing, and Filled permanent Teeth (DMFT) and the number of Decayed permanent Teeth (DT) as the outcome variables.
As time-variant factors, household income, maternal employment status, psychological distress of caregivers on the K6 scale [Kessler et al., 2002], and the frequency of brushing teeth and the frequency of drinking juice in children were assessed at each wave via questionnaires. The frequency of drinking juice was answered by the children, while other variables were answered by the caregivers. The variables were categorized as follows: household income (<3.0, 3.0–5.9, 6.0–9.9, ≥10.0 million JPY, and unknown; 130 JPY was equivalent to 1 USD); maternal employment status (full-time, part-time, self-employed/side work/other, and not employed); caregivers' psychological distress (K6 score <5 and K6 score ≥5); the frequency of brushing teeth of children (twice or more a day and less than twice a day); and the frequency of drinking juice of children (drink every day and not drink every day). These variables were included in the model as covariates.
Statistical Analysis
A difference-in-differences analysis was performed to examine the impacts of the pandemic on dental caries in permanent teeth of children. Individual fixed effects were included in the model. Hence, time-invariant confounders, such as sex and the educational attainment of parents, were considered. The models take the form:
where yij indicates dental caries for a child i in grade j; cohort is an indicator variable taking 1 for the COVID-19 exposed cohort and 0 for the COVID-19 unexposed cohort; grade is an indicator variable taking 1 for the observation in the sixth grade and 0 for the observation in the fourth grade; W indicates individual fixed effects; and X indicates time-variant covariates. Under the parallel trend assumption, β3 is interpreted as the causal effect of the COVID-19 pandemic on child dental caries. Three models were constructed to examine whether the measured time-variant factors explain the association: crude model (model 1), a model adjusting for household income and the employment status of mothers (model 2), and a model further adjusting for psychological distress of caregivers and the frequency of brushing teeth and the frequency of drinking juice in children (model 3).
While the COVID-19 exposed cohort covered all 69 public elementary schools in the city, the COVID-19 unexposed cohort covered only nine schools, and this difference may violate the parallel trend assumption. Therefore, to check whether the assumption was plausible, the numbers of DMFT and DT in the COVID-19 exposed cohort were compared between the nine schools and the rest. In addition, as a robustness check, sensitivity analysis was conducted by difference-in-differences analysis using only the data of children from the same nine schools. All analyses were performed with Stata MP, version 17.0 (StataCorp LLC).
Results
Table 1 describes the demographic characteristics of the study participants in the fourth grade. There was no significant difference in dental caries in permanent teeth between the two cohorts in the fourth grade: the means (standard deviation) of DMFT were 0.241 (0.714) and 0.242 (0.746) for the COVID-19 unexposed and exposed cohorts, respectively; and those of DT were 0.083 (0.389) and 0.083 (0.433) for the COVID-19 unexposed and exposed cohorts, respectively. Boys remained 52.9% in the COVID-19 unexposed cohort and 49.6% in the COVID-19 exposed cohort. Household income in the fourth grade was significantly higher in the COVID-19 exposed cohort than in the COVID-19 unexposed cohort. Additionally, the mothers of the COVID-19 exposed cohort were more likely to have full-time jobs. There was no significant difference in the frequency of brushing teeth or drinking juice in children between the COVID-19 unexposed and exposed cohorts. Psychological distress of caregivers was higher in the COVID-19 unexposed cohort than in the COVID-19 exposed cohort.
Table 1.
Demographic characteristics of each cohort at grade 4; N = 3,481
| Total N = 3,481 N (%) | Cohort |
p value | ||
|---|---|---|---|---|
| COVID-19 unexposed cohorta N = 399 (11.5%) N (%) | COVID-19 exposed cohortb N = 3,082 (88.5%) N (%) | |||
| DMFT, mean (SD) | 0.242 (0.743) | 0.241 (0.714) | 0.242 (0.746) | 0.964 |
| DT, mean (SD) | 0.083 (0.428) | 0.083 (0.389) | 0.083 (0.433) | 0.999 |
| Sex | 0.219 | |||
| Boy | 1,740 (50.0) | 211 (52.9) | 1,529 (49.6) | |
| Girl | 1,741 (50.0) | 188 (47.1) | 1,553 (50.4) | |
| Household income (million JPY) | 0.015 | |||
| <3.0 | 356 (10.2) | 42 (10.5) | 314 (10.2) | |
| 3.0–5.9 | 1,116 (32.1) | 156 (39.1) | 960 (31.1) | |
| 6.0–9.9 | 1,296 (37.2) | 137 (34.3) | 1,159 (37.6) | |
| ≥10.0 | 455 (13.1) | 41 (10.3) | 414 (13.4) | |
| Unknown | 258 (7.4) | 23 (5.8) | 235 (7.6) | |
| Mother's employment status | 0.018 | |||
| Full-time | 784 (22.5) | 65 (16.3) | 719 (23.3) | |
| Part-time | 1,670 (48.0) | 209 (52.4) | 1,461 (47.4) | |
| Self-employed/side work/other | 258 (7.4) | 31 (7.8) | 227 (7.4) | |
| Not employed | 769 (22.1) | 94 (23.6) | 675 (21.9) | |
| Frequency of brushing teeth | 0.658 | |||
| Twice or more a day | 2,631 (75.6) | 298 (74.7) | 2,333 (75.7) | |
| Less than twice a day | 850 (24.4) | 101 (25.3) | 749 (24.3) | |
| Frequency of drinking juice | 0.170 | |||
| Not drink everyday | 2,694 (77.4) | 298 (74.7) | 2,396 (77.7) | |
| Drink everyday | 787 (22.6) | 101 (25.3) | 686 (22.3) | |
| Caregivers’ psychological distress | 0.035 | |||
| No (K6 score <5) | 2,352 (67.6) | 251 (62.9) | 2,101 (68.2) | |
| Yes (K6 score ≥5) | 1,129 (32.4) | 148 (37.1) | 981 (31.8) | |
COVID-19, coronavirus disease 2019; DMFT, Decayed, Missing, and Filled permanent Teeth; DT, Decayed permanent Teeth; JPY, Japanese yen; SD, standard deviation.
Children who were in the fourth grade in 2016 and in the sixth grade in 2018, i.e., the cohort did not experience the pandemic.
Children who were in the fourth grade in 2018 and in the sixth grade in 2020, i.e., the cohort that experienced the pandemic.
Figure 2 illustrates the change in child dental caries from the fourth to sixth grades by cohort. The average DMFT of the COVID-19 unexposed cohort increased from 0.241 to 0.308, while that of the COVID-19 exposed cohort increased from 0.242 to 0.422. The average DT of the COVID-19 unexposed cohort increased from 0.083 to 0.085, while that of the COVID-19 exposed cohort increased from 0.083 to 0.144.
Fig. 2.
Average and 95% confidence interval of the number of dental caries by grade and cohort. COVID-19, coronavirus disease 2019; DMFT, Decayed, Missing, and Filled permanent Teeth; DT, Decayed permanent Teeth.
Table 2 exhibits the impacts of the COVID-19 pandemic on dental caries. The increment in DMFT from the fourth to sixth grades was greater in the COVID-19 exposed cohort than in the COVID-19 unexposed cohort by 0.112 (95% confidence interval [CI]: 0.011, 0.213). The estimate remained significant after adjusting for household income and the employment status of mothers in each grade (model 2, coefficient: 0.115; 95% CI: 0.014, 0.216). The frequency of brushing teeth and the frequency of drinking juice in children and psychological distress of caregivers did not explain the association (model 3, coefficient: 0.116; 95% CI: 0.015, 0.216).
Table 2.
Impacts of the COVID-19 pandemic on dental caries; N = 6,962 observations of 3,481 individuals
| Model 1 |
Model 2 |
Model 3 |
||||
|---|---|---|---|---|---|---|
| coeff. (95% CI) | p value | coeff. (95% CI) | p value | coeff. (95% CI) | p value | |
| DMFT | ||||||
| Impact of COVID-19 pandemica | 0.112 (0.011, 0.213) | 0.029 | 0.115 (0.014, 0.216) | 0.026 | 0.116 (0.015, 0.216) | 0.024 |
| DT | ||||||
| Impact of COVID-19 pandemica | 0.059 (–0.002, 0.120) | 0.057 | 0.060 (–0.001, 0.121) | 0.053 | 0.060 (–0.001, 0.121) | 0.053 |
Model 1: crude; model 2: adjusted for household income and mother's employment status; model 3: model 2 + frequency of brushing teeth, frequency of drinking juice, and caregiver's psychological distress. COVID-19, coronavirus disease 2019; Coeff., coefficient; CI, confidence interval; DMFT, Decayed, Missing, and Filled permanent Teeth; DT, Decayed permanent Teeth.
Interaction term of cohort and grade.
As for DT, the increment was greater in the COVID-19 exposed cohort than in the COVID-19 unexposed cohort by 0.059 (95% CI: −0.002, 0.120) although not statistically significant. The estimate remained similar after adjusting for household income and the employment status of mothers (model 2, coefficient: 0.060; 95% CI: −0.001, 0.121). The frequency of brushing teeth and the frequency of drinking juice in children and psychological distress of caregivers did not explain the association (model 3, coefficient: 0.060; 95% CI: −0.001, 0.121).
Online supplementary Table S1 (for all online suppl. material, see www.karger.com/doi/10.1159/000528005) presents the average DMFT and DT among the COVID-19 exposed cohort, stratified by the same nine schools as the COVID-19 unexposed cohort and the rest. The average DMFT and DT in the fourth grade were similar between these school categories. The increment in DMFT was 0.154 in the nine schools, while it was 0.183 in the rest, and DT increased by 0.011 in the nine schools and 0.068 in the rest. As online supplementary Table S2 shows, sensitivity analysis using the data from the same nine schools indicated that, after adjusting for all covariates, DMFT increased more in the COVID-19 exposed cohort than in the COVID-19 unexposed cohort by 0.094 (95% CI: −0.012, 0.200), although it was not statistically significant. The difference in the increase of DT was small and not statistically significant (coefficient: 0.013; 95% CI: −0.062, 0.089).
Discussion
The present study is the first to report that the COVID-19 pandemic increased child dental caries. Elementary school children who experienced the pandemic had greater increases in dental caries compared with the same age cohort 2 years earlier. Average DMFT and DT were similar between the two cohorts in the fourth grade, supporting the parallel trend assumption. The findings were robust to adjusting for time-variant factors, including household socioeconomic status, oral health-related behaviors of children, and psychological distress of caregivers.
Several studies have explored the impacts of the COVID-19 pandemic on oral health. The disruption of access to dental care has been actively discussed since the early stage of the pandemic [Kranz et al., 2021]. The interruption of regular dental visits due to a concern about the COVID-19 pandemic was associated with poor periodontal conditions [Iwasaki et al., 2021]. Another study has reported that dental pain was more prevalent among people whose income was reduced by the pandemic and that psychological distress was a major mediator of the association [Matsuyama et al., 2021]. As for children, the fear of COVID-19 among parents was associated with poor oral health-related quality of life [Samuel et al., 2021]. These previous studies have measured oral health outcomes only after the pandemic. The present study utilized dental caries measured before and after the pandemic and compared the change with the other cohort at the same age 2 years earlier. Hence, the causal effects of the pandemic on child dental caries were elucidated.
The effects of the COVID-19 pandemic on child dental caries were not explained by household socioeconomic status, psychological distress of caregivers, or the frequency of brushing teeth and the frequency of drinking juice in children. This suggests that the pandemic affected child dental caries through pathways other than these factors. Reductions in dental care provision for children were reported in the early stage of the pandemic [Hopcraft and Farmer, 2021], which may have a role in the association. In Japan, the total number of dental visits declined rapidly in April and May 2020 and recovered to the previous year's level in August [Health Insurance Claims Review and Reimbursement Services, 2022], although there are no data only for school children. The reduction in dental care utilization among children may partially explain the results of the present study, particularly for untreated dental caries. Meanwhile, the difference in DT was smaller than that in DMFT, suggesting other mechanisms by which the pandemic increased child dental caries. Change in sugar intake from food is one of the possible pathways. Food intake remains at 75% of sugar intake among Japanese school children [Takeichi et al., 2012]. School lunches are provided on weekdays, but during the state of emergency, school lunches were not provided, and a study has verified that children's frequency of eating meat, fish, eggs, and vegetables significantly decreased [Horikawa et al., 2021]. Their consumption of sugar-added cereals or pastries might increase instead. While the quantitative shape of the dose-response curve between sugar intake and dental caries in children has not yet reached a conclusion [Sheiham and James, 2014a; van Loveren, 2019], a study has affirmed that each additional 5 g of sugar intake per day was associated with a 1% higher probability of developing dental caries for 3 years among US children [Szpunar et al., 1995]. Although free sugar consumption among Japanese children aged 4–14 years is 31.5 g per day [Fujiwara et al., 2018] and is lower than in Western countries, a recent study has reported a linear relationship between the amount of sugar intake and dental caries even in the population at low risk of dental caries [Bernabé et al., 2016]. The dietary behavior of children would partly explain the findings of the present study. Another potential pathway is that the pandemic reduced the psychological room of caregivers to provide proper care for child health, which is associated with dental caries [Matsuyama et al., 2020]. Nonetheless, the diverse impacts of the COVID-19 pandemic are still being investigated, and further research is needed to assess the pathways leading to child dental caries.
Despite being largely preventable, the burden of oral diseases has been neglected globally [Watt et al., 2019]. The global spread of COVID-19 and the radical change in society could have affected oral diseases, such as child dental caries; however, there is a substantial scarcity of research about this issue. In Japan, 40.4% of elementary school children had experienced dental caries in 2020 [Ministry of Education, Culture, Sports, Science and Technology, 2020], and the pandemic might influence that. Further longitudinal follow-up is required to evaluate the effects of the pandemic on child dental caries.
Several limitations must be mentioned. First, the difference-in-differences analysis relied on the parallel trend assumption. This assumption is supported by the fact that the COVID-19 exposed and unexposed cohorts had a similar number of DMFT and DT in the fourth grade, thereby suggesting that they had a similar history of dental caries until the age of 10 years. Our analysis may underestimate the impacts of the COVID-19 pandemic on dental caries because child dental caries have been declining on average in Japan [Ministry of Education, Culture, Sports, Science and Technology, 2020].
Second, the COVID-19 exposed cohort covered all public elementary schools in the city, while the COVID-19 unexposed cohort covered only nine schools. The nine schools were selected by the local city governments, considering representativeness in terms of social and geographical environments in the city. In fact, among the COVID-19 exposed cohort, DMFT and DT were similar between the nine schools and the rest, thereby asserting that they were comparable regarding dental caries. Moreover, although not statistically significant, the point estimates from the sensitivity analysis using only data from the nine schools elucidated that the increment in DMFT was larger in the COVID-19 exposed cohort than in the COVID-19 unexposed cohort. Further research is required to investigate the reason why the difference in DT was less remarkable.
Third, dental health checkups in 2020 were delayed due to the pandemic. Schools are generally required to complete it by the end of June; however, due to the pandemic, it can be delayed till March 2021 (the end of the Japanese school year 2020). This might contribute to the greater increase of DMFT in the COVID-19 exposed cohort in the present study, considering that DMFT accumulates over time. A previous review estimated that annual increments in DMFT ranged from 0.06 to 0.34 for children and adolescents who had <1 DMFT at 12 years of age [Hummel et al., 2019]. More than 50% of the elementary schools in Adachi City conducted the 2020 dental health checkup in September. Thus, the delay in dental health checkups may partially explain the findings of the present study.
Fourth, the duration that the children were affected by the COVID-19 pandemic might be too short for dental caries development. According to the review on sugar consumption and child dental caries, most studies have evaluated the incidence of dental caries for 1 year or more [Moynihan and Kelly, 2014], while permanent teeth with a shorter period of post-eruption are more susceptible to dental caries [Sheiham and James, 2014b]. Future longitudinal follow-up is necessary to evaluate the long-term impacts of the pandemic on child dental caries. Lastly, the relationship between the COVID-19 pandemic and dental caries might differ in other areas of Japan. The restriction due to the pandemic was generally stricter in Tokyo than in other prefectures. Further studies in other areas of Japan and other countries are also needed.
In conclusion, this study found a greater increase in dental caries among children who experienced the COVID-19 pandemic. Child dental caries are a significant public health issue in Japan and other countries. Further longitudinal follow-up is required to evaluate the impacts of the COVID-19 pandemic on child dental caries.
Statement of Ethics
The present study was approved by the Ethics Committee at Tokyo Medical and Dental University (M2016-284-02). Informed consent was obtained from the parents of all participants via completion of the survey. Nonconsent to participate was noted via an opt out checkbox in the questionnaire. This consent process was approved by the Ethics Committee at Tokyo Medical and Dental University (M2016-284-02).
Conflict of Interest Statement
The authors have no conflicts of interest to declare.
Funding Sources
This study was supported by a Health Labour Sciences Research Grant; Comprehensive Research on Lifestyle Disease from the Japanese Ministry of Health, Labour and Welfare (H27-Jyunkankito-ippan-002); Research of Policy Planning and Evaluation from the Japanese Ministry of Health, Labour and Welfare (H29-Seisaku-Shitei-004); Innovative Research Program on Suicide Countermeasures (IRPSC); Grants-in-Aid for Scientific Research from the Japan Society for the Promotion of Science (JSPS KAKENHI Grant No. 16H03276, 16K21669, 17J05974, 17K13245, 19K19310, 19K14029, 19K19309, 19K20109, 19K14172, 19J01614, 19H04879, 20K13945, 21H04848, and 21K18294); St. Luke's Life Science Institute Grants; the Japan Health Foundation Grants; and Research-Aid (Designated Theme), Meiji Yasuda Life Foundation of Health and Welfare.
Author Contributions
Yusuke Matsuyama contributed to conception and design, analysis and interpretation, and drafted the manuscript. Aya Isumi and Satomi Doi contributed to data acquisition, project administration, interpretation, and critically revised the manuscript. Takeo Fujiwara contributed to the conception and design, data acquisition, funding acquisition, project administration, interpretation, and critically revised the manuscript. All authors gave final approval and agreed to be accountable for all aspects of the work.
Data Availability Statement
All data generated or analyzed during this study are included in this article and its online supplementary material. Further inquiries can be directed to the corresponding author.
Supplementary Material
Supplementary data
Acknowledgments
We are particularly grateful to the staff members and central office of Adachi City Hall for conducting the survey. We would like to thank everyone who participated in the surveys. In particular, we would also like to thank Mayor Yayoi Kondo, Mr. Syuichiro Akiu, Mr. Hideaki Otaka, and Ms. Yuko Baba of Adachi City Hall, all of whom contributed significantly to completion of this study.
Funding Statement
This study was supported by a Health Labour Sciences Research Grant; Comprehensive Research on Lifestyle Disease from the Japanese Ministry of Health, Labour and Welfare (H27-Jyunkankito-ippan-002); Research of Policy Planning and Evaluation from the Japanese Ministry of Health, Labour and Welfare (H29-Seisaku-Shitei-004); Innovative Research Program on Suicide Countermeasures (IRPSC); Grants-in-Aid for Scientific Research from the Japan Society for the Promotion of Science (JSPS KAKENHI Grant No. 16H03276, 16K21669, 17J05974, 17K13245, 19K19310, 19K14029, 19K19309, 19K20109, 19K14172, 19J01614, 19H04879, 20K13945, 21H04848, and 21K18294); St. Luke's Life Science Institute Grants; the Japan Health Foundation Grants; and Research-Aid (Designated Theme), Meiji Yasuda Life Foundation of Health and Welfare.
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Data Availability Statement
All data generated or analyzed during this study are included in this article and its online supplementary material. Further inquiries can be directed to the corresponding author.