Reviewing ecosystems of evidence: synthesising the evidence on the commercial determinants of health from a complex systems perspective

The Commercial Determinants of Health (CDoH) are the systems, practices, and pathways through which commercial actors drive health and equity. This includes their influence on systems of evidence production and dissemination (evidence ecosystems) in order to protect and promote commercial interests. In the Commercial Determinants of Health and Evidence Synthesis (CODES) methodological guidance, we provided advice for conducing CDoH relevant evidence syntheses, from developing a protocol to reporting the review and planning an update. This follow-up paper considers reasons and practical implications for integrating a complex systems perspective in such reviews. This commentary describes how a complex systems perspective can benefit research, including evidence synthesis related to the CDoH, by embracing the complexity of the real world, understanding interventions in context, rendering visible the corporate playbook, and exposing the power dynamics that drive inequity. We then reflect on the practical implications of adopting a complex systems approach in CDoH evidence synthesis, including drawing on a systems lens and/or incorporating specific systems methods in the review. This commentary complements existing CODES guidance in highlighting considerations for conducting CDoH relevant evidence synthesis from a complex systems perspective. It can help interpreting such reviews and raise awareness of how commercial actors can shape evidence ecosystems, particularly evidence synthesis. Having a robust evidence base that considers systems elements and dynamics will support effective action to address the CDoH, improve public health and reduce inequity at scale.