Major depressive disorder (MDD) is an important public health problem among adolescents and young adults, and its increasing prevalence underscores the need for region-specific and age-specific interventions. Despite its increasing burden, comprehensive data on regional and longitudinal trends in MDD among adolescents are scarce. This study analyzed global, regional, and national trends in MDD incidence, prevalence, and disability-adjusted life years (DALYs) among individuals aged 10–24 from 1990 to 2021, while examining differences by gender, age, socio-demographic factors, and emerging risk factors to guide targeted mental health strategies. With data from the 2021 Global Burden of Disease Study, we conducted an analysis of age-standardized incidence, prevalence, and DALYs due to MDD by sex, age group, and 21 geographic regions with a special focus on sociodemographic index (SDI) levels, which measures development on a scale from low to high. Key risk factors, such as bullying and intimate partner violence, were also assessed in order to understand their contribution to the burden of MDD. Between 1990 and 2021, the global burden of MDD increased substantially. Prevalence rose by 56.36% globally, particularly among men and young adults aged 20–24 years, with the largest increases observed in Eastern Sub-Saharan Africa (184.26% increase). Incidence grew by 56.11%, with Eastern Sub-Saharan Africa experiencing the steepest rise compared to slower increases in other regions. DALYs also increased by 56.32%, with the greatest burden observed in Eastern Sub-Saharan Africa. Bullying and intimate partner violence were leading contributors to DALYs across all regions. Bullying and childhood sexual abuse increased MDD-related DALYs, with bullying peaking at ages 10–14, while childhood sexual abuse had a higher impact on females, rising sharply after 2006. Post- 2020, all metrics (prevalence, incidence, and DALYs) rose sharply, particularly in high-SDI regions, likely due to the specific impacts of the COVID- 19 pandemic, such as prolonged lockdowns, increased social isolation, and disruptions to mental health services. This study highlights the need for culturally sensitive mental health policies focusing on prevention and early intervention, while also providing insights to improve resource allocation and support further research on adolescent mental health. Not applicable.

Backgrounds: Various family factors have been identified in association with school bullying and the involvement of children and adolescents in bullying behaviors.Methods: A total of 11,919 participants (female = 6671, mean age = 15) from 22 middle schools in Suzhou City, China completed the questionnaire. The associations between structural family factors (family socio-economic status, living arrangement, number of siblings, whether they were local residents/migrants, had an urban/ruralhukou [a household registration system in China], parental and maternal education levels, and other various bullying-related constructs (i.e. bullying witnessing, bullying involvement, bystander intervention, and fear of being bullied) were all examined. Odds ratios (ORs) adjusted for covariates were calculated for the four bullying-related constructs (bullying witness, bullying involvement, bystander intervention, and reactions to being bullied) using structural family factors.Results: The result showed that all demographic household characteristics were associated with bullying at school except for being from a single-child family. Adolescents from rural families witnessed more bullying incidents than those from local families (OR = 1.35, 95% CI: [1.09, 1.68]). Adolescents who come from migrant families (OR = 1.12, 95% CI: [1.07, 1.43]) with a rural hukou (OR = 1.31, 95% CI: [1.00, 1.74]) and low parental education levels (OR = 1.42, 95% CI: [1.01, 2.57]) were more likely to be bullies. Adolescents who came from migrant families (OR = 1.37, 95% CI: [1.03, 1.82]), with low maternal education levels (OR = 1.42, 95% CI: [1.06, 1.91]) engaged in more negative bystander intervention behaviors. Furthermore, adolescents with less educated mothers experienced a higher fear of being bullied (neverversussometimes: OR = 1.33, 95% CI: [1.00, 1.85];neverversususuallyOR = 1.39, 95% CI: [1.01, 1.20]).Conclusions: A systematic examination of the relationship between school bullying and demographic household characteristics may be used to inform school policies on bullying, such as training management on the importance of paying attention to adolescents from disadvantage household backgrounds. Identifying demographic factors that may predict bullying can also be used to prevent individuals from becoming involved in bullying and reduce the related negative consequences from being bullied.

Background: Post-partum depression (PPD) is a growing mental health concern worldwide. There is little evidence in the Chinese context of the relationship between paternal PPD and maternal PPD. Given the growing global concerns this relationship requires further exploration. Methods: A survey was conducted with 950 total couples from March 2017 to December 2018. The study was conducted using a standardized questionnaire that included basic demographic information, information on the relationship between the mother-in-law and daughter-in-law, marital satisfaction (both maternal and paternal), and PPD symptoms. Structural Equation Modelling (SEM) analysis was used to explore the underlying mechanism for PPD symptoms in mothers and fathers. Results: In 4.4% of the couples both the wife and the husband showed depressive symptoms. Maternal marital satisfaction showed a significant mediating effect on paternal PPD (B = -0.114, p < 0.01), and there was a direct effect of maternal PPD on paternal PPD (B = 0.31, p < 0.001). Conclusions: This is the first study to investigate the possible correlation between maternal PPD, mother-in-law and daughter-in-law relationship satisfaction, maternal marital satisfaction, paternal marital satisfaction, and paternal PPD. It is important for future PPD interventions to target both maternal and paternal mental health, as well as the mechanisms identified that can lead to PPD.