Gender inequalities in trajectories of depressive symptoms among young people in London and Tokyo: a longitudinal cross-cohort study

Background Research suggests gender inequalities in adolescent mental health are context dependent. This implies they may be preventable through social/structural change. However, there is also some evidence that gender mental health gaps are larger in ostensibly more gender equal societies, e.g., 2-3-fold larger in the UK vs. Japan. Using data and methods that overcome important limitations of existing evidence, we tested the hypothesis that gender inequalities in depressive symptom trajectories are larger in London than in Tokyo, and that these differences are not due to incomparable measurement. Methods We used three waves of data from representative adolescent cohorts in Tokyo (TTC; n =2,813) and London (REACH; n =4,287) ( n= 7,100; age 11-16y). We used multigroup and longitudinal confirmatory factor analysis to examine measurement invariance of the 13-item Short Mood and Feelings Questionnaire (SMFQ) across cohorts, genders, and ages. Latent growth models compared depressive symptom trajectories of boys and girls in London and Tokyo. Outcomes Scalar invariance was well-supported. In London, gender inequalities in depressive symptoms were evident at age 11y (girls: +0·8 [95% CI: 0·3-1·2]); in Tokyo, the difference emerged between 11-14y. In both places, the disparity widened year-on-year, but by age 16y was around twice as large in London. Annual rate of increase in depressive symptoms was around four times steeper among girls in London (1·1 [0·9-1·3]) vs. girls in Tokyo (0·3 [0·2-0·4]). Interpretation Gender inequalities in emotional health are context dependent and may be preventable through social/structural change. Funding Japanese Society for the Promotion of Science; Economic and Social Research Council. Evidence before this study Women are around two-to-four times more likely than men to experience emotional problems such as depression and anxiety. Our understanding of the causes is surprisingly limited. Typically, these gender inequalities in emotional health emerge in early adolescence, at around the age of puberty, so much research has focussed on biological explanations. However, a growing body of evidence suggests gender inequalities in adolescent mental health may be context dependent, varying in size – and sometimes direction – across countries. This implies it may be possible to prevent the excess of mental distress among teenage girls through social/structural change. However, there is also some evidence to suggest that gender inequalities in teenage mental health are larger , on average, in countries with higher levels of societal gender equity, e.g., around 2-3 times larger in the UK (which ranks 15th on global gender equity) compared with Japan (ranked 125th). Reasons for this seemingly paradoxical trend are unclear. However, there are important limitations to the international evidence that preclude robust inference about the contexts and conditions that give rise to (and those that mitigate and prevent) gender inequalities in emotional health. It is mostly cross-sectional, relates to older age groups, or – importantly – fails or is unable to robustly examine measurement invariance between countries. We reviewed the reference lists in two successive reviews (published in 2000 and 2017) on the causes of gender inequalities in depression and searched PubMed for original and review articles published as of January 2023. Search terms included: gender inequalities (sex/gender differences, inequalities, disparities, etc.) AND mental health (mental distress, depression, depressive symptoms, etc.) AND young people (child*, adolesc*, youth, etc.) AND international comparisons (international comparisons, cross-cohort, cross-cultural, etc.). We screened titles and abstracts to identify studies with longitudinal data on mental health in population-based adolescent samples. We found: one cross-sectional study reporting gender inequalities in mental distress and wellbeing at age 15 years in 73 countries, with measurement invariance considered at the regional level (e.g., Americas, Eastern Mediterranean); one cross-sectional study of all age groups (except children under 12) in 90 countries, with no examination of measurement invariance; and four longitudinal studies comparing gender inequalities in mental health across countries in mid-adolescence, that either (a) used unrepresentative samples, (b) compared countries with very similar levels of societal gender equity, or (c) did not examine – or only partly supported – measurement invariance between countries. Added value of this study We used three waves of data from large, representative cohorts of young people in Tokyo and London and examined (a) the extent to which a widely used measure of depressive symptoms is invariant (comparable) across place, gender, and age, and (b) whether inequalities in depressive symptom trajectories between adolescent boys and girls are larger in London than in Tokyo. We found strong evidence that inequalities in depressive symptom trajectories between adolescent boys and girls are around twice as large, and may emerge earlier, among young people in London than in Tokyo. Notably, the annual rate of increase in depressive symptoms from age 11 to age 16 was around four times steeper among girls in London than among girls in Tokyo. Importantly, we found little evidence to suggest these differences are due to incomparable measurement. We co-wrote this paper with ten young people, five in London and five in Tokyo, and their perspectives are integrated throughout and presented in the Supplement. Implications of all the available evidence There is strong evidence that the size and course of gender inequalities in emotional health are driven by social/structural context. Against a backdrop of high and rising rates of emotional health problems among young women and girls in many countries, there is an urgent need to understand the contexts and conditions that enable young girls to thrive. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This work was supported by funding from the Invitation Program for Foreign Researchers at the Tokyo Metropolitan Institute of Medical Science. REACH is supported by the UK Economic and Social Research Council (ESRC) Centre for Society and Mental Health at Kings College London (ES/S012567/1); and the European Research Council (ERC) (REACH 648837). TTC is supported by funding from Grant-in-Aid for Scientific Research on Innovative Areas (23118002; Adolescent Mind & Self-Regulation) from the Ministry of Education, Culture, Sports, Science and Technology of Japan; JSPS KAKENHI (Grant Numbers JP16HY06395, 16H06398, 16H06399, 16K21720, 16K15566, 17H05931, JP21H05171, JP21H05173, JP21H05174 and JP22H05211); JST-Mirai Programme (Grant number JPMJMI21J3); and the International Research Center for Neurointelligence (WPI-IRCN) at the University of Tokyo Institutes for Advanced Study (UTIAS). ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: Ethics Committees of the Tokyo Metropolitan Institute of Medical Science (no.: 12-35), the University of Tokyo (10057), and SOKENDAI (the Graduate University for Advanced Studies; 2012002), and the Psychiatry, Nursing and Midwifery Research Ethics Subcommittee, Kings College London (15/16-2320), gave ethical approval for this work. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes TTC: Data from TTC is archived in the Tokyo Metropolitan Institute of Medical Science. Collaboration in data analysis and publication will be welcome through specific research proposals sent to the research committee. The initial contact point for collaborations is Dr Atsushi Nishida (nishida-at@igakuken.or.jp). REACH: We welcome requests from researchers wishing to access REACH data for specific research projects or collaborations. Our data access policy, which aims to make REACH data as accessible as possible while adhering to legal and ethical principles and protecting the privacy of schools and participants, can be found at www.thereachstudy.com/information-for-researchers.html. The application should be submitted to Professor Craig Morgan (craig.morgan@kcl.ac.uk).