Supplementary Material for: Interaction between serum cotinine, magnesium intake with childhood asthma: a cross-sectional study

Introduction: Serum cotinine and magnesium intake are often associated with childhood asthma. This study evaluated the interaction between serum cotinine, magnesium intake with childhood asthma. Methods: This cross-sectional study included 14,159 subjects from National Health and Nutrition Examination Survey 2005-2018. Serum cotinine levels were classified according to the lower quartile: ≤0.2089 ng/mL as low-level and >0.2089 ng/mL as high-level. Magnesium intake were categorized as high (>98 mg/1000kcal) or low level (≤98 mg/1000kcal) based on the upper quartile. Adopted the weighted logistic regression analyses to analyze the association between cotinine, magnesium intake and childhood asthma. Additionally, the combined effect of cotinine and magnesium intake on childhood asthma risk was examined. The stratified analyses based on gender, body mass index and family history of asthma to further examine the relationship between cotinine, magnesium intake and childhood asthma. Results: The prevalence of asthma was approximately 17.56%. Compared to low-level cotinine, high-level cotinine was associated with asthma [odds ratio (OR) = 1.25, 95% confidence interval (CI): 1.04-1.50]. Low-level magnesium intake was related to asthma compared with high-level magnesium intake (OR=1.21, 95%CI: 1.04-1.40). Using interaction analysis, we also found that the combined effect of cotinine and magnesium intake was associated with childhood asthma risk, and the interaction between high-level cotinine and low-level magnesium intake was associated with the highest risk of childhood asthma (OR=1.35, 95%CI: 1.04-1.74). Additionally, this interaction was also found in male, overweight/non-overweight and those with family history of asthma. Conclusion: There was an interaction between serum cotinine and magnesium intake on childhood asthma. The results suggested that implementing smoking bans in certain settings (e.g., communities, schools) and promoting the consumption of magnesium-rich foods may be effective strategies for preventing childhood asthma.