In contrast to sadness, which most people experience from time to time, and despair or pain experienced during adversity, depression is a mental health condition (Herrman et al., 2022). Depression causes profound, lasting suffering for those affected and is associated with premature death from physical illness and suicide (Wright et al., 2021). Beyond the individual, depression also affects families and communities, impairing social functioning and economic productivity (Dwyer et al., 2020; Philipson et al., 2020). Depression is the leading cause of health-related disability and a major contributor to the global disease burden (Collaborators, 2018; Korczak et al., 2023; Krause et al., 2021). Approximately 4.7 % of the world's population experience an episode of depression within the course of 12-months (Herrman et al., 2022). However, policy attention and resources are woefully inadequate. Even in high-income countries, <20 % of patients with major depression receive effective care, and in low- and middle-income countries, this proportion is <10 % (Vigo et al., 2020).

A proportion of depression cases begin in childhood and increase dramatically during adolescence (Korczak et al., 2023; Morken et al., 2021). By 19 years old, an estimated 25 % of teenagers have experienced a depressive episode, according to research (Hetrick et al., 2021). Depressive episodes in pre-adulthood often predict relationship challenges, academic and career difficulties, poor quality of life, and more physical and mental illness, as well as more depressive episodes and a higher risk of self-harm and suicide (Fitzpatrick et al., 2023; Hawrilenko et al., 2021; Hetrick et al., 2021). In adolescents, subthreshold depression is more common than diagnostic threshold depressive disorders, with prevalence twice as high (Gee et al., 2020; Noyes et al., 2022). A recent systematic review found that subthreshold depression is similar to major depressive disorder in terms of functional impairment, brain changes, suicidal ideation, comorbidity, and genetic predisposition, emphasizing that subthreshold depression also has important clinical implications (Noyes et al., 2022). Therefore, early identification and intervention of depression in children and adolescents is regarded as a global health priority and public health challenge (Davaasambuu et al., 2020; Eckshtain et al., 2020; Miller and Campo, 2021).

Most of the recent systematic reviews reporting on the prevalence of depression or depressive symptoms in children or adolescents focused on one country (Mahmudi et al., 2021; Wang et al., 2019) or special group (e.g., obese children, cancer patients) (Al-Saadi et al., 2022; Barker et al., 2019; Chen et al., 2023), and two systematic reviews covering the world also had some limitations, including: less rigorous studies were included (Shorey et al., 2022); only studies reporting on at least three mental disorders were included (Polanczyk et al., 2015). To our knowledge, there are no studies that provide a comprehensive review of the global burden of depression or depressive symptoms in children and adolescents.

The purpose of this systematic review and meta-analysis is to estimate the global burden of depression or depressive symptoms (hereafter depression) in children and adolescents based on currently available high-quality evidence, and to provide its temporal and regional distribution to help policymakers assess the scope and severity of this problem and focus on the far unmet mental health needs of children and adolescents.