There is continued interest in identifying dysregulated biomarkers that mediate associations between adverse childhood experiences (ACEs) and negative long-term health outcomes. However, little is known regarding how ACE exposure modulates neural biomarkers to influence poorer mental health outcomes in ACE-exposed children. To address this, we performed a systematic review and meta-analysis of the impact of ACE exposure on Brain Derived Neurotrophic Factor (BDNF) levels - a neural biomarker

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... ciated with the onset of mood disorders. Twenty-two studies were selected for inclusion within the systematic review, ten of which were included in meta-analysis. Most included studies retrospectively assessed impacts of childhood maltreatment in clinical populations. Sample size, BDNF protein levels in ACE-exposed and unexposed subjects, and standard deviations were extracted from ten publications to estimate the BDNF ratio of means (ROM) across exposure categories. Overall, no significant difference was found in BDNF protein levels between ACE-exposed and unexposed groups (ROM: 1.05; 95% CI: 0.91-1.22). Non-significant elevation of BDNF levels in ACE-exposed subjects was observed among studies specifically investigating childhood maltreatment and among studies measuring BDNF in serum, but these analyses were limited by high between-study heterogeneity. Studies that measured BDNF levels in subjects prior to age 20 revealed elevated levels in the ACE-exposed group, which was not observed in studies measuring BDNF levels later in life. These results support continued investigation into the impact of ACE exposure on neural biomarkers and highlight the potential importance of analyte type and timing of sample collection on study results.