Food insecurity and elevated nicotine exposure among U.S. tobacco users: Evidence from NHANES

• Food insecurity severity was linked to ∼ 10% higher serum cotinine among US tobacco users. • Depression neither mediated nor moderated the food insecurity–cotinine association. • Income moderated effects, with food insecurity predicting greater nicotine exposure mainly above poverty. • Among smokers, food insecurity weakened the dose–response slope of smoking frequency on cotinine. Tobacco use and food insecurity (FI) frequently co-occur and may influence each other bidirectionally. Most prior research has emphasized tobacco use as a driver of FI, typically relying on self-reported measures. This study examined associations between FI and serum cotinine, a biomarker of nicotine exposure, and evaluated potential mediating and moderating factors. Data from the 2015–2018 National Health and Nutrition Examination Survey were analyzed for 2,149 adult tobacco users. Cotinine concentrations were log-transformed and modeled with survey-weighted generalized linear models, adjusted for sociodemographic covariates, depression, and body mass index. Mediation was tested with causal mediation analysis and structural equation modeling, and moderation with interaction terms. Each unit increase in FI severity was associated with an ∼ 10% increase in cotinine after adjustment (p = 0.018). Depression neither mediated nor moderated the FI–cotinine association. Poverty-income ratio significantly moderated the relationship (p = 0.009): the positive FI–cotinine slope was strongest at higher incomes, while at or below the poverty line FI was not significantly associated with cotinine. In smoker subsamples, FI also moderated the smoking frequency–cotinine slope, with the most food-insecure participants showing the shallowest dose–response relationships. FI is associated with elevated cotinine concentrations, but effects depend on household economic resources and how smoking behavior translates into nicotine uptake. Stabilizing food security may be critical for reducing tobacco-related health disparities.