Association between blood lead and gastrointestinal cancers among US adults: A cross-sectional study based on NHANES 2003-2016.

Lead is a widespread environmental toxin known to cause various health issues, but its relationship with gastrointestinal (GI) cancers remains poorly understood. We aimed to investigate the association between blood lead levels and the prevalence of GI cancer in a representative sample of US adults. This cross-sectional study included 27,721 adults from the 2003-2016 National Health and Nutrition Examination Survey. Weighted multivariable logistic regression models, subgroup analysis, and restricted cubic spline regression were used to analyze the relationship between blood lead levels and GI cancer risk. GI cancer was identified based on self-reported physician diagnoses. Among participants, 251 individuals reported a GI cancer diagnosis. Higher blood lead levels were positively associated with GI cancer prevalence (fully adjusted odds ratio per unit increase: 1.11, 95% CI: 1.06-1.17, P < .001). Restricted cubic spline analysis demonstrated a nonlinear relationship, with a sharp increase in cancer risk at lower blood lead concentrations (2-3 µg/dL) and a plateau at higher levels. Subgroup analyses were conducted across sex, education level, alcohol intake, and poverty-income ratio. The positive association between blood lead and GI cancer was consistent across these strata, and no interaction remained significant after Benjamini-Hochberg correction (all q > 0.67). Blood lead concentration was positively associated with the prevalence of GI cancer in US adults. Even concentrations below current reference values may be associated with GI cancer, underscoring the need for prospective cohorts and mechanistic studies to clarify causality and to guide stricter exposure thresholds.