Polychlorinated biphenyls (PCBs) exposure and cognitive function in adults: A systematic review of epidemiologic evidence and risk of bias assessment

BACKGROUND: Polychlorinated biphenyls (PCBs) are persistent organic pollutants known for their environmental longevity and neurotoxicity. Although developmental exposure has been extensively studied, the cognitive impacts of PCBs exposure in adult and aging populations remain less understood. OBJECTIVES: This systematic review evaluates the epidemiologic evidence linking PCBs exposure to cognitive function, with an emphasis on neurocognitive decline and dementia risk in adults. METHODS: Following PRISMA guidelines, we searched PubMed and Web of Science for human epidemiological studies published in English up to November 2024. Inclusion criteria focused on empirical studies investigating associations between PCBs exposure and cognitive outcomes in elderly population. Data were synthesized narratively, and a domain-based risk of bias assessment was conducted using the Navigation Guide methodology. RESULTS: Twenty-four studies were included in the final analysis, spanning diverse populations and exposure contexts (occupational, environmental and dietary). Six studies examined the association between PCBs exposure and dementia or Alzheimer's disease, with overall mixed findings. Some studies reported associations in specific subgroups, particularly among individuals with higher exposure levels or among women, while others reported null relationships. For cognitive outcomes, memory, processing speed and executive functions were the frequently assessed domain; however, findings across studies were inconsistent and did not demonstrate a clear pattern of association. A smaller number of studies assessed cognitive decline, with similarly heterogeneous results. Risk of bias was generally low for exposure and outcome assessment but higher for confounding and other validity domains. Notably, inconsistent cognitive testing methods and limited longitudinal data constrained causal inference. CONCLUSION: Current epidemiologic evidence is insufficient to support a consistent association between PCBs exposure and dementia or cognitive performance in aging populations. Further well-designed longitudinal studies using standardized cognitive assessments are needed to clarify potential relationships. PROSPERO REGISTRATION NUMBER: CRD420251003803.