Recent tobacco exposure and type 2 inflammatory biomarkers in asthma: differential associations with FeNO and eosinophils (A cross-sectional analysis of NHANES 2007–2012)

The relationship between recent tobacco exposure intensity and type 2 inflammatory markers (fractional exhaled nitric oxide [FeNO], eosinophils [EOS]) in asthma, and whether smoking modulates their correlation, remains unclear. Using 2007–2012 NHANES data, 1551 asthmatic patients were stratified by serum cotinine (tobacco exposure biomarker) into quintiles. We analyzed correlations of cotinine with FeNO and EOS, and explored its effect on the FeNO–EOS association. Patients in the highest serum cotinine quintile (Q5, ≥154 ng/mL) had significantly lower odds of elevated FeNO (adjusted OR = 0.17, 95% CI: 0.08–0.36) but higher odds of elevated eosinophil counts (unadjusted OR = 2.15, 95% CI: 1.41–3.28) compared to those in the lowest quintile (Q1, <0.012 ng/mL). No significant associations were found for FeNO in the intermediate quintiles (Q2–Q4). The correlation between FeNO and eosinophils was gradually weakened with increasing serum cotinine levels and became nonsignificant in the highest cotinine quintile. Interaction analysis (p = 0.02) identified tobacco exposure as a significant effect modifier of the FeNO-eosinophil association. Reduced FeNO levels and elevated eosinophils are associated with high-level recent tobacco exposure, but not with low-moderate level recent tobacco exposure. Tobacco exposure modifies the correlation between FeNO and eosinophils.