Exposure to Armed Conflict in Childhood vs Older Ages and Subsequent Onset of Major Depressive Disorder

IMPORTANCE: This study offers a rare opportunity to evaluate life-course differences in the likelihood of developing major depressive disorder (MDD) after exposure to georeferenced neighborhood-level violence during an armed conflict. OBJECTIVE: To examine age cohort (age <11 vs ≥11 years) differences in associations of neighborhood-level violence with subsequent depression onset, independently of individual exposure and other key characteristics. DESIGN, SETTING, AND PARTICIPANTS: The Chitwan Valley Family Study is a population-representative panel study (1995 to present) conducted in Western Chitwan in Nepal, a low-income country that experienced a medium-intensity armed conflict from 2000 to 2006. Data for violent events were collected during the armed conflict and were linked to lifetime histories of MDD (collected in 2016-2018). The present cohort study analyzes 10 623 participants within 151 neighborhoods, systematically selected and representative of Western Chitwan. All residents aged 15 to 59 years at MDD assessment were eligible (response rate, 93%). Data analysis was performed from May 2019 to July 2020. EXPOSURES: Georeferenced number of armed conflict–related physical beatings within 1 km of residential neighborhood. MAIN OUTCOMES AND MEASURES: The main outcome was onset of MDD, as defined by Diagnostic and Statistical Manual of Mental Disorders (Fourth Edition), during or after the conflict, stratified by children (aged <11 years) and older individuals (aged ≥11 years), assessed by the Nepal-specific World Mental Health–Composite International Diagnostic Instrument 3.0 with a life history calendar. RESULTS: In total, 10 623 participants (5745 female [54.08%]; 4074 [38.35%] aged <11 years at the conflict start) contributed 171 899 person-years of exposure to the risk of MDD. Two or more beatings occurred within 1 km of 15 neighborhoods (9.9%). Discrete-time survival models showed that children (but not older individuals) living in neighborhoods with 2 or more beatings had a higher likelihood of developing MDD than those who lived in a community with no beatings (odds ratio, 1.82; 95% CI, 1.17-2.84; P = .008); there was also a significant interaction between age group and neighborhood beatings (odds ratio, 1.85; 95% CI, 1.27-2.70; P = .001). A confirmatory, multivariable, multilevel matching analysis showed a neighborhood association for children (z = −2.66; P = .008), but not older individuals (z = −0.454; P = .65). The mean (SE) incidence of MDD among children living in neighborhoods with 2 or more beatings nearby was 12.69% (2.37%) vs 5.08% (1.56%) in the matched unexposed sample. CONCLUSIONS AND RELEVANCE: The youngest individuals may be the most at risk during times of violence, with mental health consequences lasting long after conflicts have subsided and should be a priority for population-level interventions. Future research should consider other disorders, other types of violence, and elderly individuals.