In recent years, the prevalence of asthma in children has continued to increase, and one of its major determinants is, in fact, environmental: secondhand smoke. However, although tobacco exposure is widely recognized as a risk factor for asthma, its precise biological impact on asthma risk, along with possible mediating factors such as BMI, has been less clear.
The data extracted from NHANES, for 2011–2018, include a nationally representative sample of children in the United States between the ages of 3 and 12 years. Key variables that were analyzed include serum cotinine concentration, physician-diagnosed asthma, and BMI.
A comprehensive statistical approach was followed that entailed:
Weighted multivariable logistic regression to estimate the association between cotinine and asthma.
Subgroup analyses to evaluate consistency across age, sex, and demographic categories.
Perform smooth curve fitting and threshold effect analysis to investigate non-linearity and saturation points.
Mediation analysis to quantify the proportion of asthma risk explained by BMI.
This approach allowed very accurate identification of nonlinear relationships and pathway contributions, which enhanced clarity on the way tobacco exposure influences paediatric asthma.
Results
The findings demonstrated a nonlinear association between serum cotinine and asthma risk.
Risk increased with rising cotinine values until a saturation point of a Log₂-serum cotinine value of −0.3, corresponding to a serum cotinine concentration of 0.81 ng/mL, beyond which the increase in risk leveled off, indicating a maximal biological effect of low-level exposure.
The mediation analysis showed that 12.21% of the mediating effect between serum cotinine and asthma was contributed by BMI, suggesting that part of this increased risk may operate through pathways related to weight status, inflammation, or metabolic changes.
These findings cumulatively point to a dose-dependent relation between tobacco exposure and childhood asthma, with BMI as a significant but partial mediator.
This study confirms that higher serum cotinine levels are significantly associated with elevated risk for childhood asthma and that BMI acts as a mediator for the association. The identification of a nonlinear exposure threshold and quantification of the mediating role of BMI provide strong evidence that exposure to tobacco smoke continues to be a critical yet preventable factor in pediatric asthma, with meaningful implications for clinical screening and public health policy.
Reference:
Chen, F., Ye, J., Zhang, L., Lin, B.-Q., Gu, L., & Liu, W. (2025). Associations of serum cotinine with asthma risk in US children: a mediation analysis of body mass index. Respiratory Medicine, 108502, 108502.
https://doi.org/10.1016/j.rmed.2025.108502
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