Association of Lead in Drinking Water With Head and Neck Cancer in the United States

OBJECTIVE: Heavy metals are established human carcinogens, and lead exposure via drinking water has been linked to esophageal cancer. This study aimed to investigate the association between various levels of lead exposure in drinking water and incidence rates of head and neck cancers (HNC) in the United States. STUDY DESIGN: Ecological study. SETTING: County-level data from 608 US counties included in the Surveillance, Epidemiology, and End Results (SEER) database. METHODS: County-level HNC incidence rates and sociodemographic variables were obtained from SEER. Drinking water lead concentrations were sourced from the Environmental Protection Agency (EPA) and spatially interpolated using inverse distance weighting (IDW). Tobacco and alcohol use data were retrieved from the Centers for Disease Control and Prevention (CDC). Flexible semi-parametric regression models were used to assess the association between lead exposure and HNC incidence, adjusting for known confounders. Multiple comparisons were addressed using Holm's method, and sensitivity analyses were performed using ordinary least squares (OLS) models. RESULTS: Higher lead concentrations were significantly associated with increased incidence of oral and pharyngeal cancers (incidence rate ratio [IRR] = 1.05, 95% CI 1.00-1.08, P < .01), gum and mouth cancers (IRR = 1.03, 95% CI 1.00-1.08, P = .02), and esophageal neoplasms (IRR = 1.01, 95% CI 1.00-1.03, P = .02). These associations remained significant after multiple testing correction and were consistent across OLS models. CONCLUSION: This is the first study to demonstrate that even low-level lead exposure below EPA limits in drinking water is associated with increased incidence of specific HNC subsites. These findings highlight the importance of continued investigation into environmental determinants of HNC. LEVEL OF EVIDENCE: II.