Sensitivity analyses.

α-klotho is an anti-aging protein. The correlation between smoking, smoking cessation and serum α-klotho levels remains controversial. The aim of this study was to investigate the association between smoking, smoking cessation and serum α-klotho levels. This cross-sectional study finally included 4877 participants, aged 40–79 years, who participated in the National Health and Nutrition Examination Survey studies from 2013 to 2016. Of these, 2312 (47.4%) were men and 894 (18.3%) were current smokers, and the mean age of the participants was 57.8±10.7 years. Multivariate linear regression modeling was used to assess the association between smoking, smoking cessation and serum α-klotho levels. After adjustment for multiple confounders, this study observed that smoking was negatively associated with serum α-klotho levels (β: -58.3; 95% confidence interval CI: -82.0 to -34.6; pp-value for the interaction between smoking and race on serum klotho levels was found to be less than 0.001. The correlation between smoking, smoking cessation and serum α-klotho levels remained stable after propensity score matching (β: -54.1; 95% CI: -81.5 to -26.7; pp