Association between serum cotinine and learning disability in children aged 4-15 years: A secondary data analysis...

While prior studies suggest links between secondhand smoke (SHS) exposure and developmental impairment, evidence linking objective biomarkers of SHS exposure to learning disability (LD) in children remains limited. This study investigates the association between serum cotinine - a validated biomarker of SHS exposure - and the higher likelihood of LD in US children.

This secondary analysis utilized cross-sectional data from the National Health and Nutrition Examination Survey (NHANES) 1999-2002, including 2573 children aged 4-15 years. Multivariable logistic regression models were implemented to evaluate the association between serum cotinine and parent-reported LD diagnoses. The dose-dependent relationship between cotinine and LD was analyzed using smooth curve fitting. Subgroup analyses were evaluated to assess robustness.

Multivariable logistic regression analysis revealed that each unit increase in log-transformed cotinine was associated with a 1.81-fold increase in the odds of LD (AOR=1.81; 95% CI: 1.21-2.70, p<0.01). Children in the highest cotinine quartile exhibited 2.38-fold higher odds of LD compared to those in the lowest quartile (AOR=2.38; 95% CI: 1.23-4.58, p=0.01). Dose-response analysis revealed a linear relationship between log cotinine and LD (p for nonlinearity=0.20). Subgroup analyses further confirmed the stability of these results (p for interaction >0.05).

The findings indicate a significant association between serum cotinine and an increased likelihood of LD in US children. The dose-dependent and linear nature of this relationship advocate for stricter smoke-free policies and targeted educational campaigns to reduce potential neurodevelopmental harms in children.