Olivia Remes, João Francisco Mendes, Peter Templeton
7 min
Depression is a leading cause of global disability, yet our understanding of its origins remains fragmented. This review synthesizes 470 documents published between 2017 and 2020 to map the diverse factors contributing to the condition. By moving beyond single-discipline perspectives, the authors illustrate that depression is not the result of one isolated cause but rather a 'web of causation' where biological, psychological, and social factors constantly interact.
The review categorizes these determinants into three primary spheres:
The findings highlight that these determinants are deeply interlinked. For instance, social deprivation can lead to poor nutrition, which in turn influences inflammatory markers, potentially triggering biological pathways to depression. The authors emphasize the importance of a 'lifecourse perspective,' noting that early-life stress can create long-term vulnerabilities that are later compounded by genetic predispositions and environmental stressors. This integrated framework is essential for clinicians and public health policymakers to move toward more effective, person-centered, and targeted interventions.
Depression is one of the leading causes of disability, and, if left unmanaged, it can increase the risk for suicide. The evidence base on the determinants of depression is fragmented, which makes the interpretation of the results across studies difficult. The objective of this study is to conduct a thorough synthesis of the literature assessing the biological, psychological, and social determinants of depression in order to piece together the puzzle of the key factors that are related to this condition. Titles and abstracts published between 2017 and 2020 were identified in PubMed, as well as Medline, Scopus, and PsycInfo. Key words relating to biological, social, and psychological determinants as well as depression were applied to the databases, and the screening and data charting of the documents took place. We included 470 documents in this literature review. The findings showed that there are a plethora of risk and protective factors (relating to biological, psychological, and social determinants) that are related to depression; these determinants are interlinked and influence depression outcomes through a web of causation. In this paper, we describe and present the vast, fragmented, and complex literature related to this topic. This review may be used to guide practice, public health efforts, policy, and research related to mental health and, specifically, depression.
Sam: [confirming, quiet conviction] Precisely. The paper argues that unless we adopt an integrated systems approach—one that accounts for the lifecourse perspective—our interventions will continue to address only the symptoms while the underlying grid remains overloaded.
Alex: [curious, leaning in] That sounds like a shift from the traditional search for a smoking gun—like a specific gene or biomarker. If the literature is this fragmented, how did they actually manage to synthesize such a wide range of fields?
Sam: [grounded, analytical] They used a systematic review methodology to map findings across genetics, immunology, and social epidemiology. The key insight is that distal factors, like chronic poverty or social isolation, act as persistent stressors that trigger proximal biological cascades, such as HPA axis dysregulation and systemic inflammation. Think of it like a power grid: a surge in one neighborhood trips the breakers in the substation, leading to a city-wide blackout.
Alex: [processing, deliberate] So the biological markers we see in the clinic—like inflammation or neuroplasticity deficits—might actually be the downstream consequences of those social and psychological stressors?
Sam: [nodding, voice precise] Exactly. The paper suggests that when these stressors persist, they alter the brain's neuroplasticity and cognitive processing, which then feeds back into the patient's social behavior, creating a cycle that is incredibly difficult to break with a single intervention.
Alex: [probing, analytical] But if the literature is as heterogeneous as they claim, how much weight can we put on these findings? A referee would surely point out that these studies use vastly different metrics for depression.
Sam: [acknowledging the point, measured] That is the paper's most honest limitation. The authors acknowledge that the lack of standardized measurement tools across fields makes direct comparison difficult. However, the value here isn't in a single effect size—it is in the scale of the synthesis. By mapping these connections, they demonstrate that the primary barrier to clinical progress is not a lack of data, but the silos that prevent us from seeing these bidirectional loops.
Alex: [reflective, slower] So a clinician focusing solely on SSRIs might be missing the social isolation or rumination patterns that are keeping the HPA axis in a state of chronic hyperactivation.
Sam: [confirming, quiet conviction] Precisely. The paper argues that unless we adopt an integrated systems approach—one that accounts for the lifecourse perspective—our interventions will continue to address only the symptoms while the underlying grid remains overloaded. <break time="0.6s" /> The *mechanism* of recovery, therefore, requires untangling these feedback loops across biological, psychological, and social domains simultaneously.
Alex: [curious, leaning in] That sounds like a shift from the traditional search for a smoking gun. If the literature is this fragmented, how did they synthesize such a wide range of fields?
Sam: [grounded, analytical] They used a systematic review to map genetics, immunology, and social epidemiology. The key insight is that distal factors, like chronic poverty, act as stressors that trigger biological cascades, like systemic inflammation. Think of it like a power grid: a surge in one neighborhood trips the breakers, leading to a city-wide blackout.
Alex: [processing, deliberate] So the markers we see in the clinic—like inflammation—might actually be the *downstream* consequences of those social stressors?
Sam: [nodding, voice precise] Exactly. The paper suggests these stressors alter neuroplasticity, which feeds back into social behavior, creating a cycle that is difficult to break with a single intervention.
Alex: [probing, analytical] But if the literature is heterogeneous, how much weight can we put on these findings? A referee would point out that these studies use vastly different metrics for depression.
Sam: [acknowledging the point, measured] That is the paper's most honest limitation. The authors acknowledge that the lack of standardized measurement tools makes direct comparison difficult. However, the value here isn't in a single effect size—it is in the *scale* of the synthesis. They demonstrate that the primary barrier to clinical progress is the silos preventing us from seeing these bidirectional loops.
Alex: [reflective, slower] So a clinician focusing solely on SSRIs might be missing the social isolation keeping the HPA axis in a state of chronic hyperactivation.
Sam: [confirming, quiet conviction] Precisely. Unless we adopt an integrated systems approach, our interventions will continue to address only the symptoms while the underlying grid remains overloaded. <break time="0.