The impact of family depression history and childhood adversities on the risk of depression in adulthood among 1,461,034 individuals

Objective: To investigate the separate and combined impact of family major depression (MD) history and ten childhood adversities (CA) on the risk of adult MD. Methods: All Danish citizens born 1977–2000 with known parental identity were followed from their 18th birthday until diagnosis of MD, migration, death, or December 31, 2022, in nationwide registers. Exposures were family MD history and ten selected CAs. Family MD history was operationalized using the ICD 8th Revision codes 296.09, 296.29, 298.09, and 300.49 or 10th Revision codes F32.0-F33.9. CAs were; relative family poverty, long-term parental unemployment, foster care, parental alcohol abuse, parental drug abuse, parental and sibling somatic illness, parental long-term unemployment, parental separation, and parental and sibling death. Multivariable Poisson regression was applied to estimate the incidence rate ratio (IRR) with 95 % CI of first-time MD. Results: The study included 1,461,034 individuals (Male: 51.5 %). During a mean follow-up of 14.5 years (SD ± 7.2), 50,231 (3.5 %) of cohort members were diagnosed with first-time MD in adulthood. Family MD history was associated with an IRR of 1.94 (95 % CI [1.88–2.00]) for MD. In all models, both CAs and family MD, separately and combined, were associated with an increased IRR for MD. The IRRs for individuals with a family MD history with or without CA, respectively, were generally relatively comparable. Conclusions: Individuals exposed to family MD history and CAs are at increased risk of MD. However, the associations between family MD and onset of MD in adulthood remain largely unchanged regardless of the presence of any of the ten CAs.