Secondhand smoke exposure in never-smokers: A cross-sectional and prospective cohort study of chronic kidney disease prevalence and all-cause mortality in affected patients.

Chronic kidney disease (CKD) is a major global health burden, yet the association of secondhand smoke (SHS) exposure with CKD among never-smokers remains incompletely characterized. This cross-sectional and prospective cohort study analyzed 13,276 never-smoking adults from the National Health and Nutrition Examination Survey from 1999 to 2020. Multivariable logistic regression was used to evaluate CKD prevalence, and Cox proportional hazards models were used to evaluate all-cause mortality among participants with CKD. Sensitivity and subgroup analyses were conducted to assess the robustness of the findings. Moderate SHS exposure was associated with higher CKD prevalence (odds ratio = 1.37, 95% confidence interval [CI]: 1.07-1.76; P = .01). Among 1630 participants with CKD, moderate and heavy SHS exposure were associated with higher all-cause mortality (hazard ratio [HR] = 2.03 [95% CI: 1.23-3.36] and HR = 1.80 [95% CI: 1.11-2.93], respectively). Each doubling of serum cotinine concentration was associated with a 4% higher mortality hazard (HR = 1.04, 95% CI: 1.01-1.08; P = .02). Sensitivity analyses incorporating sampling weights and additional covariates supported the overall pattern of associations. Among never-smoking adults, moderate SHS exposure was associated with higher CKD prevalence; among those with CKD, higher SHS exposure was associated with greater all-cause mortality. These observational findings support further prospective investigation and reinforce the importance of minimizing SHS exposure.