Interpreting evidence on the association between multiple adverse childhood experiences and mental and physical health outcomes in adulthood: protocol for a systematic review assessing causality

Research suggests that adverse childhood experiences can have a lasting influence on children's development that result in poorer health outcomes in adulthood. Like other exposure-outcome relationships, however, there is uncertainty about the extent to which the relationship between adverse childhood experiences and health is causal or attributable to other factors. The aim of this systematic review is to better understand the nature and extent of the evidence available to infer a causal relationship between adverse childhood experiences and health outcomes in adulthood. A systematic review of evidence from cross-sectional and longitudinal studies will be conducted to examine the association between multiple adverse childhood experiences and mental and physical health outcomes in adulthood. A comprehensive search for articles will be conducted in four databases (Medline, CINAHL, PsycInfo and Web of Science) and Google Scholar. We will include studies published since 2014: (1) of adults aged 16 years or over with exposure to adverse childhood experiences before age 16 years from general population samples; (2) that report measures across multiple categories of childhood adversity, including both direct and indirect types and (3) report outcomes related to disease morbidity and mortality. Two reviewers will independently screen all titles and abstracts and full texts of potentially relevant studies. Included studies will be evaluated for risk of bias with the Risk Of Bias In Non-randomised Studies of Exposures tool. Data extraction will include extraction of study characteristics; measurement of adverse childhood experiences, outcome assessment and measurement of outcomes; details about confounding variables and contextual variables; methods of statistical analysis; and methods for assessing causal inference. We will carry out a meta-analysis and incorporate causal assessment with reference to the Bradford Hill criteria and the Grading of Recommendations Assessment, Development and Evaluation framework. This study is a systematic review protocol collecting data from published literature and does not require approval from an institutional review board. The findings from this systematic review will be disseminated via a peer-reviewed journal publication, professional networks and social media. CRD42024554563. [Abstract copyright: © Author(s) (or their employer(s)) 2025. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ Group.]