Chronic heavy metal exposure and chronic kidney disease: integrating epidemiology, mechanisms, biomarkers, and interventions.

Abstract

Chronic kidney disease (CKD) affects over 800 million people globally. Emerging evidence suggests that chronic heavy metal exposure is a significant yet underappreciated environmental contributor. However, critical uncertainties persist. These include the precise shape of dose-response relationships, whether single-metal guidelines adequately reflect real-world mixtures, and how to translate mechanistic insights into practice. This review synthesizes evidence across epidemiology, mechanisms, biomarkers, and interventions to address these gaps. Large-scale observational studies consistently report associations between cadmium, lead, and arsenic exposure and higher CKD risk and faster eGFR decline. However, causality remains uncertain because most evidence is observational, and reverse causation and residual confounding cannot be ruled out. Dose-response curves often exhibit nonlinear features, including U-shaped and threshold patterns. Several studies have reported interactive or joint associations for metal mixtures at concentrations below some study-specific reference values, although evidence for biological synergism and regulatory inadequacy remains limited. These findings raise concerns that single-metal guidelines may not fully capture mixture effects. Candidate urinary biomarkers such as KIM-1, NGAL, and NAG have been proposed as candidate early markers of tubular injury. However, prospective studies must establish their incremental predictive value, reference ranges, reproducibility, discrimination, calibration, and clinical utility before routine clinical use can be recommended. Translational strategies, including nutritional antagonism, environmental source control, and emerging therapies, show promise in mitigating nephrotoxicity. This review offers three main contributions: a proposed integrative mechanistic framework that treats oxidative stress as one node within a broader network and epigenetic persistence as a hypothesis requiring human validation. A critical synthesis of mixture toxicity that raises the possibility, but not proof, that single-metal standards may not fully capture mixture effects. And a research agenda for evaluating candidate biomarkers as potential early markers, pending prospective validation. Integrating causal inference, mechanistic research, biomarker evaluation, and public health measures may help reduce the burden of metal-related kidney disease and inform potential revisions of environmental safety standards, but current evidence remains insufficient to assert causality or mandate regulatory change.

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