Exploring depression in adults over a decade: a review of longitudinal studies

Depression, as a prevalent global mental health disorder, stands as one of the main causes of disability worldwide, imposing significant individual, societal, and economic burdens. While its heterogeneous nature is well recognized, growing evidence highlights the importance of understanding depression trajectories, which describe the long-term course and variability of depressive symptoms over time. These trajectories are shaped by a complex interplay of biological, psychological, and social factors. However, despite extensive research on depression's prevalence and risk factors, a comprehensive synthesis of trajectory patterns, their determinants, and their long-term implications remains limited. This review systematically examines the existing literature on depression trajectories in adults, identifying key influences such as age, gender, socioeconomic status, early life experiences, social support, physical health, lifestyle factors, and external stressors, including pandemics. By integrating findings from longitudinal and epidemiological studies, this review provides novel insights into the bidirectional relationship between depression and chronic health conditions, underscoring the need for a holistic, trajectory-based approach to mental health care. The findings have important implications for clinical practice, public health, and future research. Recognizing distinct trajectory patterns may facilitate earlier identification of high-risk individuals, inform the development of personalized interventions, and optimize the allocation of mental health resources. Furthermore, by elucidating the complex interconnections between depression and broader health determinants, this review establishes a foundation for advancing targeted, evidence-based interventions aimed at reducing the long-term burden of depression, particularly among vulnerable populations.