Taniguchi et al. International Journal for Equity in Healthhttps://doi.org/10.1186/s12939-024-02234-z(2024) 23:150

International Journal for Equity
in HealthOpen Access

RESEARCH

Different trends in suicide rates among
foreign residents in Japan and Japanesecitizens during the COVID-19 pandemic
Yuta Taniguchi1,2,3, Nanako Tamiya3,4*, Masao Iwagami3,4,5, Kazumasa Yamagishi4,6,7, Atsushi Miyawaki4,8,Rie Masuda3,4,9, Tomomi Kihara4,6, Jun Komiyama1,3, Hirokazu Tachikawa4,10, Hideto Takahashi3,4,11 and Hiroyasu Iso2,6
Abstract
Background Suicide rates in Japan have increased during the COVID-19 pandemic, and foreign residents may be
more vulnerable to mental stress during such crises. Therefore, we aimed to compare the trends in suicide rates
during the COVID-19 pandemic between foreign residents and Japanese citizens.
Methods Vital statistics of Japan data from January 1, 2016 to December 31, 2021 were used to calculate quarterly
sex-specific suicide rates for foreign residents and Japanese citizens. An event-study analysis was conducted toevaluate whether suicide rates during the COVID-19 pandemic increased compared to pre-pandemic estimates;
foreign residents and Japanese citizens were compared using difference-in-difference-in-differences estimates.
Results Between 2016 and 2021, 1,431 foreign residents and 121,610 Japanese citizens died from suicide in Japan.
Although the suicide rate for foreign residents was lower than that for Japanese citizens, Korean residents, whocomprise approximately half of the foreign decedents, had largely higher suicide rates than Japanese citizens. The
event-study analysis indicated that suicide rates increased among foreign residents for both men and women, andcontinued for men by the end of 2021. In Japanese citizens, after a decline in suicide rates in the second quarter of
2020, suicide rates increased both among men and women, and lasted for women until the fourth quarter of 2021.
The difference-in-difference-in-differences analyses confirmed the initial decline in the second quarter of 2020 insuicide rate only in Japanese men and women, and the persistent increase through 2021 in foreign men.
Conclusions We found differential trends in suicide rates between foreign and Japanese men and women during
the COVID-19 pandemic featuring a persistent increase in foreign men. Suicide prevention measures should befocused on these high-risk subpopulations.
Keywords COVID-19, Suicide, Japan, Foreign residents, Japanese citizens*Correspondence:
Nanako Tamiya
ntamiya@md.tsukuba.ac.jp
Full list of author information is available at the end of the article© The Author(s) 2024. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use,sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) andthe source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in thisarticle are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not includedin the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you willneed to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The
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in this article, unless otherwise stated in a credit line to the data.

Taniguchi et al. International Journal for Equity in Health(2024) 23:150

Background
During the coronavirus disease 2019 (COVID-19) pandemic, Japan was one of the unique countries that showed
an increase in suicide rates [1–9], with suicide rates before
the pandemic ranking top among G7 countries and fifthamong the 38 OECD countries [10]. Earlier studies reported
that the increased suicide rates during the COVID-19 pandemic were especially prominent among women [2, 3, 5–7,
9], the youth [1, 3, 5], housewives [3], urban residents [5],and persons living alone [5]. However, to the best of ourknowledge, no studies have compared the situations ofsuicide between foreign residents and native residents. In
general, foreign residents are assumed to be vulnerable
populations, owing to the inequity of social, economic, andmedical care conditions [11–13]. Indeed, since the COVID19 pandemic began in 2020, foreign residents have beenreported to experience higher morbidity and mortality due
to the virus [14], higher levels of distress, [15] and limitedaccess to healthcare services, including COVID-19 vaccination [16, 17]. Considering the vulnerability of foreign
residents during the COVID-19 pandemic, it is conceivablethat foreign residents in Japan may have also experienced
an increase in the suicide rates during the pandemic, evenlarger and more persistent than that experienced by Japanese citizens.
Despite increasing concern regarding the mental healthof foreign residents, previous studies in Japan are limited,
because they did not distinguish foreign residents and Japanese citizens when assessing the trends in suicide rates
during the pandemic. Therefore, in this study, we aimed toaddress the following research questions; (1) Did suicide
rates among foreign residents in Japan increase during the
COVID-19 pandemic? and (2) Did the change in suicide
rates vary between foreign residents and Japanese citizens?
Methods
Data source and study population

We acquired the vital statistics death data of Japan fromJanuary 1, 2016 to December 31, 2021 from the Ministry of
Health, Labour, and Welfare, under the Statistics Act, Article 33. Vital statistics of Japan records every death, including date and cause, as well as the deceased’s age, sex, andnationality [18]. The validity of the vital statistics data is rigorously maintained under the supervision of the Ministry of
Health, Labour, and Welfare.
We identified individuals who died by suicide, using thetenth revision of the International Statistical Classificationof Diseases (ICD-10) codes X60–X84. The individuals withmissing data for age, sex, or nationality were excluded fromthe analysis.
Outcome measure

The outcome measure was the sex-specific crude suicide
rate in each quarter (January to March, April to June, July

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to September, and October to December) from 2016 to
2021. We calculated the quarterly suicide rate for both foreign residents and Japanese citizens by dividing the numberof suicides by the population in each quarter. For Japanesecitizens, we extracted the data on populations from themonthly population estimates [19], summed up the monthly
numbers and took the average for each quarter. For foreign
residents, as the population of foreign residents is reported
only twice a year (June and December) by the Statistics on
Foreign National Residents in Japan [20], we substituted the
population in June for the second and third quarter, and thatin December for the fourth quarter and the first quarter ofthe following year. Population of foreign residents included
any foreign national who stayed in Japan during the periodof measurement.
Statistical analysis

First, we compared the basic characteristics of foreign
residents and Japanese citizens who died from suicidefrom 2016 to 2021. Second, we calculated and plotted thesex-specific suicide rate for each quarter of the observed
years for foreign residents and Japanese citizens separately. We also stratified the study participants into three
age groups (< 40, 40–59, or ≥ 60 years old). We then calculated the sex-specific suicide rates for Koreans, whowere reported as having higher suicide rates than otherforeign residents in Japan and Japanese citizens before
the COVID-19 pandemic [21, 22]. Third, to estimate theassociation between the pandemic suicide rates by sex
and nationality (foreign or Japanese), we used an eventstudy difference-in-differences analysis (hereafter, eventstudy analysis) and compared the change in suicide rates
in the event period (first quarter of 2019 to fourth quarterof 2021; the event time was the “beginning” of the pandemic at the end of first quarter of 2020) with the three
years earlier as the control period (first quarter of 2016 to
fourth quarter of 2018). The event-study analysis allowed
us to observe a longitudinal trend of suicide rates at multiple time points after the COVID-19 pandemic by comparing the corresponding pre-pandemic period. The endof the first quarter of 2020 (April 2020) was defined as the
beginning of the COVID-19 pandemic, corresponding towhen the Japanese government declared a state of emergency [23].
We denoted the period from the first quarter (Q1) of
2019 to the fourth quarter (Q4) of 2021 as the “exposedgroup” and Q1 of 2016 to Q4 of 2018 as the “control
group.” In the exposed group, the pandemic time frames
were compared with pre-pandemic control time frames
in terms of changes in suicide rates between the averageof five quarters before the pandemic (Q1–Q4 of 2019 andQ1 of 2020) and each of seven subsequent quarters (Q2–
Q4 of 2020 and Q1–Q4 of 2021). These were then compared with the changes in the corresponding quarters

Taniguchi et al. International Journal for Equity in Health(2024) 23:150

from the control group. We estimated a linear regression model with heteroskedasticity-robust standard
errors (see Supplementary Method for more details on
the statistical analyses). Fourth, to examine whether the
event-study estimates at each quarter varied between theforeign residents and Japanese citizens, we calculated thedifference-in-difference-in-differences estimates (triple
difference estimator), which is measured as the difference
between two difference-in-differences or event-study
estimates [24]. We also conducted the stratified analyses
for Koreans and other foreign nationals.
Analyses were performed using Stata 17 (StataCorp,
TX, USA) and Microsoft Excel for Mac 16.67 (Microsoft,
WA, USA).

Results
We identified 123,041 individuals (1,431 foreign residents and 121,610 Japanese citizens) who died by suicide in Japan between 2016 and 2021, after excluding 313

Page 3 of 9

persons with missing variables of age, sex, or nationality.
As shown in Table 1, the proportion of women among
foreign residents and Japanese citizens was 37.5% and31.2%, respectively. The median age was 48 (interquartile
range [IQR], 31–63) for foreign men, 50 (35–63) for foreign women, 52 (38–68) for Japanese men, and 55 (39–72) for Japanese women. The annual number of deaths
were between 207 and 265 for foreign residents andaround 20,000 for Japanese citizens. Koreans constituted
half of the foreign residents for both sexes, and as shownin Supplementary Table 1, Koreans were more likely tobe older and unemployed, compared with other foreign
residents.
Occupation refers to the occupation of the highest
earner in the household.
As shown in Fig. 1, for both men and women, the quarterly suicide rates were higher among Japanese citizens
than foreign residents throughout the study period; thisis partly because of the higher mean age among Japanese

Table 1 Baseline characteristics of individuals who died by suicide in Japan between 2016–2021 (n = 123,041)

Age, median (IQR), year
Nationality, n (%)
Korea
China
BrazilPhilippines
United States
Thailand
Peru
United Kingdom
OthersOccupation, n (%)
Agriculture
Self-employed
Employee
Other
Not working
Unknown
Marital status n (%)
MarriedNot married
Bereaved
Divorced
Unknown
No of deaths, n (%)
2016
2017
2018
2019
2020
2021

Foreign residents (n = 1431)
Men, n (%) 895 (62.5)
Women, n (%) 536 (37.5)
48 (31–63)
50 (35–63)

Japanese citizens (n = 121,610)
Men, n (%) 83,699 (68.8)
Women, n (%) 37,911 (31.2)
52 (38–68)
55 (39–72)

451 (50.4)
114 (12.7)
79 (8.8)
24 (2.7)
33 (3.7)
10 (1.1)
6 (0.7)4 (0.5)174 (19.4)

274 (51.1)
129 (24.1)
15 (2.8)
42 (7.8)
5 (0.9)13 (2.4)
1 (0.2)2 (0.4)55 (10.3)

–
–
–
–
–
–
–
–
–

–
–
–
–
–
–
–
–
–

7 (0.8)65 (7.3)
178 (19.9)
103 (11.5)
369 (41.2)
173 (19.3)

4 (0.8)42 (7.8)
94 (17.5)
76 (14.2)
218 (40.7)
102 (19.0)3646 (4.4)
6094 (7.3)
20,961 (25.0)
11,316 (13.5)
32,948 (39.4)
8734 (10.4)

1422 (3.8)
2224 (5.9)
8383 (22.1)
4622 (12.2)
17,515 (46.2)
3745 (9.9)

288 (32.2)
368 (41.1)
31 (3.5)
137 (15.3)
71 (7.9)

198 (36.9)
169 (31.5)
57 (10.6)
93 (17.4)
19 (3.5)

31,980 (38.2)
33,470 (40.0)
5052 (6.0)
12,959 (15.5)
238 (0.3)

15,142 (39.9)
10,460 (27.6)
6780 (17.9)5475 (14.4)
54 (0.1)

146 (16.3)
133 (14.9)
147 (16.4)
146 (16.3)
156 (17.4)
167 (18.7)

81 (15.1)
74 (13.8)
98 (18.3)
78 (14.6)
107 (20.0)
98 (18.3)

14,663 (17.5)
14,354 (17.2)
13,865 (16.6)
13,711 (16.4)
13,631 (16.3)
13,475 (16.1)

6382 (16.8)
6134 (16.2)
6190 (16.3)
5764 (15.2)
6662 (17.6)
6779 (17.9)

Abbreviations: IQR, interquartile range

Taniguchi et al. International Journal for Equity in Health(2024) 23:150

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Fig. 1 Quarterly suicide rates among foreign residents in Japan and Japanese citizens from 2016–2021. Abbreviations: Q, Quarter Note: The gray dashedlines represent the beginning of the COVID-19 pandemic in Japan (April 2020)

Taniguchi et al. International Journal for Equity in Health(2024) 23:150

citizens, compared to foreign residents. When stratified byage group, such differences were evident at ages of < 40 and
40–59 years (Fig. 2). When we stratified foreign residents
into Koreans and other nationalities, Korean people experienced higher suicide rates than other foreign residents andJapanese citizens, for both men and women throughout the
study period (Supplementary Fig. 1), particularly among
men aged ≥ 60 (Supplementary Fig. 2).
Figure 3 presents the event-study analysis estimates ofthe sex-specific suicide rates among foreign residents andJapanese citizens. In the exposed group (2019–2021), we
observed increased suicide rates among foreign men in thesecond and fourth quarters of 2020 and all quarters of 2021,
and among foreign women in the third quarter of 2020,
compared to the control group (2016–2018). For Japanesecitizens, after a decline in suicide rates in the second quarter of 2020 for both men and women, suicide rates increased
among men from the fourth quarter of 2020 to the second
quarter of 2021, and among women from the third quarterof 2020 to the fourth quarter of 2021.
As shown in Table 2, the difference-in-difference-in-differences analyses showed a greater increase in suicide rates
among foreign men, compared with Japanese men, in thesecond and fourth quarters of 2020, as well as from the second to the fourth quarters of 2021. The increase in the suicide rate was larger for foreign women in the second quarter

Page 5 of 9

of 2020, and for Japanese women in the fourth quarter of
2020, followed by no difference through the end of 2021.
When we stratified foreign residents into Korean nationals and other nationalities, the event-study analysis for
Korean men showed that suicide rates increased in the
fourth quarter of 2020, and from the third to the fourth
quarters in 2021; however, we observed no differencesamong Korean women (Supplementary Fig. 3). As shownin Supplementary Table 2, the difference-in-difference-indifferences analyses confirmed the increase in suicide rates
in late 2021 among Korean men, compared with Japanesemen, until the end of 2021.

Discussion
Using the vital statistics data of Japan for the period 2016–
2021, we found differential sex-specific trends for quarterly
suicide rates during the COVID-19 pandemic from April
2020 to December 2021 between foreign residents and Japanese citizens. Suicide rates increased among foreign men
in the second and fourth quarters of 2020 and all quartersof 2021, and among foreign women in the third quarter of2020. For Japanese citizens, after an initial decline in thesecond quarter of 2020, suicide rates increased among men
from the fourth quarter of 2020 to the second quarter of2021, and among women from the third quarter of 2020 tothe fourth quarter of 2021. The difference-in-difference-indifferences analyses confirmed the initial decline in suicide

Fig. 2 Quarterly suicide rates among foreign residents in Japan and Japanese citizens from 2016–2021, by age group. Abbreviations: Q, Quarter Note: Thegray dashed lines represent the beginning of the COVID-19 pandemic in Japan (April 2020)

Taniguchi et al. International Journal for Equity in Health(2024) 23:150

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Fig. 3 Event-study estimates of suicide rates among foreign residents in Japan and Japanese citizens from 2019–2021 vs. 2016–2018. Abbreviations:
Q, Quarter. Note: The bars indicate 95% confidence intervals, and the gray dashed lines indicate the beginning of the COVID-19 pandemic (April 2020)

(2024) 23:150* P < 0.05, ** P < 0.01, ***P < 0.001

Abbreviations: DD, difference-in-differences; DDD, difference-in-difference-in-differences; CI, confidence interval; Q, Quarter

Q2, 2020
Q3, 2020
Q4, 2020
Q1, 2021
Q2, 2021
Q3, 2021
Q4, 2021-0.90*** (-1.12, -0.68)
0.18 (-0.04, 0.41)
1.24*** (1.02, 1.46)
0.44** (0.22, 0.66)
0.50* (0.28, 0.73)
0.17 (-0.05, 0.39)-0.07 (-0.29, 0.16)

0.97* (0.096, 1.85)-0.36 (-1.23, 0.52)
2.13** (1.25, 3.00)
0.91* (0.033, 1.78)
1.33* (0.46, 2.21)
0.88* (0.0035, 1.75)
1.42* (0.54, 2.29)

1.87*** (1.20, 2.54)-0.54 (-1.22, 0.13)
0.88* (0.21, 1.56)
0.47 (-0.20, 1.14)
0.83* (0.15, 1.50)
0.71* (0.03, 1.38)
1.48*** (0.81, 2.15)-0.32** (-0.46, -0.17)
0.79*** (0.64, 0.94)
1.44*** (1.29, 1.58)
0.67*** (0.52, 0.81)
0.57*** (0.43, 0.72)
0.41** (0.27, 0.56)
0.32** (0.17, 0.47)

0.91 (-0.03, 1.85)
1.31* (0.37, 2.25)
0.72 (-0.22, 1.66)
0.73 (-0.21, 1.67)
0.26 (-0.69, 1.20)
0.43 (-0.51, 1.38)
0.52 (-0.43, 1.46)

DDD estimates,
foreign residents
vs. Japanese(95% CI)
1.23** (0.51, 1.94)
0.52 (-0.19, 1.23)-0.72* (-1.43, -0.01)
0.06 (-0.65, 0.78)-0.32 (-1.03, 0.39)
0.02 (-0.69, 0.73)
0.20 (-0.51, 0.91)
Foreign residents
DD estimates(95% CI)
DDD estimates, foreign residents vs. Japanese (95% CI)

Women
Japanese citizens
DD estimates(95% CI)
Foreign residents
DD estimates(95% CI)
Men
Japanese citizens
DD estimates(95% CI)

Table 2 Difference-in-difference-in-differences (DDD) estimates of the effects of the COVID-19 pandemic on suicide rates in foreign residents and Japanese citizens

Taniguchi et al. International Journal for Equity in HealthPage 7 of 9

rates only among Japanese men and women, and the persistent increase through 2021 among foreign men. To the bestof our knowledge, this is the first study to evaluate the sexand nationality-specific trends in suicide rates during the
COVID-19 pandemic.
The lower suicide rates among foreign residents compared to Japanese citizens before and during the COVID-19
pandemic were partly due to a younger age; when stratified by age group, such trends were observed for ages < 40
and 40–59 years, but not for ages ≥ 60 years. Additionally,
Korean residents experienced higher suicide rates thanother foreign nationals or Japanese citizens, particularly
men aged ≥ 40 and women aged < 60 years. Previous studies
reported higher suicide rates in Korean residents, comparedto Japanese citizens, prior to the COVID-19 pandemic [21,22], and our results suggest that this phenomenon continued during the pandemic.
Previous studies have reported the initial decline in suicide rates during the COVID-19 pandemic in Japan [2–5, 7].
It was suggested that this may be attributable to increased
feelings of social connectedness in a time of crisis (alsocalled the “pulling-together effect”) [2–4], reduced working hours, and subsidies from the government [3]. On thecontrary, we did not observe such decline among foreign
residents, which may be due to the less availability of aforementioned protective factors. Some foreign residents could
not return to their home countries due to the cancellationof flights [25], and may have faced greater difficulties thanJapanese citizens.
It is noteworthy that the increase in the suicide rates continued for foreign men, but not for Japanese men, until theend of 2021. According to the population census of October 2020, foreign men had a higher unemployment rate
(4.9%) than Japanese men (4.3%), and they may have been
more likely to experience economic difficulties [26]. Korean
men had a particularly high unemployment rate (6.9%), andbecause around a quarter of them worked as sales or service workers [26], they may have experienced financial crisis
during the pandemic, which could had made them particularly vulnerable.
Historically, the suicide rate in Japan increased rapidly
in the late 1990s, and the Japanese government worked on
suicide prevention policies, ratifying the Basic Act on Suicide Prevention in 2006 [27]. Although the suicide rate inJapan decreased from 2011, it resurged during the COVID19 pandemic. Thus, the reinforcement of suicide prevention with a focus on socially disadvantaged populations isimportant. In this context, our study illuminated the possible importance of extending suicide prevention for foreign
residents in Japan, as well as Japanese citizens. For example,
the Ministry of Health, Labour, and Welfare of Japan published a website in Japanese that provides a wide variety of
information on available mental health services, such as
telephone consultation services [28]. However, resourcesTaniguchi et al. International Journal for Equity in Health(2024) 23:150

in other languages are still limited, despite the language
barrier being reported as the major issue for mental wellbeing among international migrants in Japan [29]. Thus,
the enhancement of multilingual information and assistance through governments and non-governmental organizations is highly recommended for socially disadvantaged
populations.
The study has several strengths. First, to our knowledge,
this is the first study to investigate trends in suicide rates
during the COVID-19 pandemic, focusing on differencesby nationalities. Besides, this study provided the most upto-date information up to the end of 2021, using the mostrecent definitive statistics of the Japanese vital statistics
available.
This study also has several limitations that must be noted.
First, the residential status or employment conditions could
vary largely among foreign residents with undocumented,
short-term, or long-term ones, and suicide risk may differ accordingly. However, we could not acquire this information. Yet, our study showed higher suicide rates among
Koreans, the majority of whom were long-term residents[20]. Second, because we did not have information on thereasons for suicide, which could be multifactorial, we could
not determine if the increases in suicide rates were caused
directly or indirectly by the COVID-19 pandemic. Still,
our findings highlight the need for the promotion of mental health services to prevent suicide for both Japanese andforeign residents. Third, although financial problems and ahistory of mental disorders were reported as risk factors for
suicide [30], we could not evaluate the differences in economic conditions or health status between Japanese citizens
and foreign residents. Differences in economic conditions
and health status may partly explain the different trends insuicide rates by nationality. Future studies using the linked
data of census, medical records, and vital statistics would
be necessary. Lastly, since the Japanese government records
the census of foreign residents only bi-annually, in June andDecember, we may have overlooked the changes in the populations of foreign residents at the quarterly level; however,
it is unknown whether the difference in census procedures
would affect the suicide rates. As a sensitivity analysis, we
calculated the quarterly suicide rate for Japanese citizens inthe same way as for foreign residents. That is, as the denominator, we used the population in June for the second andthird quarters and that in December for the fourth quarterand the first quarter of the following year. The results were
almost identical.

Conclusions
In conclusion, during the COVID-19 pandemic, we
observed an increase in suicide rates among both foreign
residents and Japanese citizens but found an initial decline
only among Japanese citizens. Our findings imply a needfor tailored mental health support as well as reasonable job

Page 8 of 9

opportunities for vulnerable populations, especially during pandemics with substantial impact on socioeconomic
conditions.
Abbreviations
ICD-10	International Statistical Classification of Diseases, Tenth Revision
IQR	Interquartile range
Q	Quarter
DD	Difference-in-differences
DDD	Difference-in-difference-in-differences
CI	Confidence interval

Supplementary Information

The online version contains supplementary material available at https://doi.
org/10.1186/s12939-024-02234-z.
Supplementary Material 1: Supplementary Method 1. Event-study
difference-in-differences analysis. Supplementary Table 1. Baselinecharacteristics of individuals who died by suicide in Japan between 2016
and 2021. Supplementary Fig. 1. Quarterly suicide rates among Koreansand other foreign nationals in Japan and Japanese citizens from 2016 to
2021. Supplementary Fig. 2. Quarterly suicide rates among Koreans andother foreign nationals in Japan and Japanese citizens from 2016 to 2021,
by age group. Supplementary Fig. 3. Event-study estimates of suicide rates
among Koreans and other foreign nationals in Japan and Japanese citizens
from 2019 to 2021 vs. 2016–2018. Supplementary Table 2. Difference-indifference-in-differences (DDD) estimates of the effects of the COVID-19
pandemic on suicide rates in Korean residents and Japanese citizens.
Acknowledgements
We would like to thank Editage (www.editage.com) for its English language
editing.
Author contributions
YT designed the study, analyzed the data, and wrote the initial draft. NT and
HI contributed to conception, acquisition of data, study design, interpretation,and revision of the manuscript. MI, KY, AM, RM, TK, JK, H.Tachikawa, and
H.Takahashi contributed to study design, interpretation, and revision of themanuscript. All authors approved the final version and had final responsibility
for the decision to submit for publication.
Funding
This study was supported by the Japanese Ministry of Health, Labour andWelfare (MHLW) Special Research Program [grant number JPMH20CA2046];
and the MHLW Research Program on Emerging and Re-emerging Infectious
Diseases and Immunization [grant number JPMH21HA2011, JPMH23HA2011
and JPMH24HA2015]. The funder played no role in the conception, design,
implementation, or reporting of the study.
Data availability
Data cannot be shared because the Japanese Ministry of Health, Labour andWelfare owns the original data and only approved its secondary use for thecurrent study. Researchers who meet the criteria may apply directly to the
Ministry for permission to use the deidentified participant data.

Declarations
Consent for publication
Not applicable.
Competing interests
The authors declare no competing interests.
Ethical approval and consent to participate
The study was approved by the Ethics Committee of the University of Tsukuba(approval no. 1754), in accordance with the Declaration of Helsinki. Because
we received anonymized data for our analyses, individual participants’Taniguchi et al. International Journal for Equity in Health(2024) 23:150

consent was waived for our study. Data were presented following the STROBE
guidelines.
Author details
1
Department of Health Services Research, Graduate School ofComprehensive Human Sciences, University of Tsukuba, 1-1-1 Tenno-dai,Tsukuba, Ibaraki 305-8575, Japan
2
Institute for Global Health Policy Research, Bureau of International Health
Cooperation, National Center for Global Health and Medicine, 1-21-1
Toyama, Shinjuku-ku, Tokyo 162-8655, Japan3
Department of Health Services Research, Institute of Medicine, Universityof Tsukuba, 1-1-1 Tenno-dai, Tsukuba, Ibaraki 305-8575, Japan
4
Health Services Research and Development Center, University ofTsukuba, 1-1-1 Tenno-dai, Tsukuba, Ibaraki 305-8575, Japan
5
Faculty of Epidemiology and Population Health, London School ofHygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, UK
6
Department of Public Health Medicine, Institute of Medicine, Universityof Tsukuba, 1-1-1 Tenno-dai, Tsukuba, Ibaraki 305-8575, Japan
7
Department of Public Health, Graduate School of Medicine, Juntendo
University, 2-1-1 Hongo, Bunkyo-ku, Tokyo 113-8421, Japan
8
Department of Public Health, Graduate School of Medicine, The
University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
9
Division of Nursing, Higashigaoka Faculty of Nursing, Tokyo Healthcare
University, 2-5-1, Higashigaoka, Meguro-ku, Tokyo 152-8558, Japan10
Department of Disaster and Community Psychiatry, Division of Clinical
Medicine, Institute of Medicine, University of Tsukuba, 1-1-1 Tenno-dai,Tsukuba, Ibaraki 305-8575, Japan
11
Faculty of Pharmaceutical Sciences, Teikyo Heisei University, 4-21-2
Nakano, Nakano-ku, Tokyo 164-8530, Japan
Received: 19 December 2023 / Accepted: 16 July 2024

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