Association between serum Klotho concentrations and asthma in middle-aged and older Americans: a cross-sectional study

BACKGROUND: Klotho, an anti-aging protein with anti-inflammatory and antioxidant properties, plays a role in asthma pathophysiology. This study investigated whether serum Klotho concentrations are associated with asthma prevalence among middle-aged and elderly Americans. METHODS: This cross-sectional study included 12,442 participants from the National Health and Nutrition Examination Survey (2007-2016). Serum Klotho was measured by ELISA and asthma was self-reported. Weighted multivariable logistic regression adjusting for demographic and clinical confounders was performed to evaluate associations. Smoothed curve fitting assessed potential nonlinear relationships. RESULTS: After adjustment for confounding variables, a significant inverse association was found between serum Klotho concentration and asthma incidence. Specifically, each unit increase in log-transformed Klotho was associated with a 48% reduction in asthma risk (odds ratio: 0.52; 95% confidence interval: 0.38-0.69). Participants in the lowest Klotho quartile had a higher prevalence of asthma than those in the highest quartile (odds ratio, 0.58; 95% confidence interval: 0.45-0.76). Subgroup analyses revealed associations between a history of cardiovascular disease and drinking status. Notably, smoothing curve analysis did not reveal a nonlinear association between Klotho levels and asthma prevalence. CONCLUSIONS: Lower serum Klotho levels are significantly associated with higher asthma prevalence in middle-aged and elderly Americans. Klotho may serve as a potential biomarker for asthma risk assessment, though prospective cohort studies are needed to establish causality.