Relation of exposure to secondhand tobacco smoke during pregnancy and early childhood with adolescents body composition and cardiometabolic health: a cohort study

Exposure to secondhand tobacco smoke (SHS) is a worldwide public health problem and children are a particularly vulnerable population due to their anatomical, physiological, and behavioral characteristics. Cotinine concentrations in saliva, blood, and hair have become the most widely used biomarkers of SHS in children. Currently, there is no consensus regarding the optimal cut-point for the classification of SHS exposure among young children. Indeed, the systematic review conducted as part of this thesis shows that serum cotinine cut-points have varied remarkably since 1985 and across the countries; the most recently used cut-point to assess SHS exposure in US children has been 0.015 ng/mL, which derives from the assay limit of detection (LOD) used by the National Health and Nutrition Examination Survey (NHANES). Considering that cotinine metabolism and clearance may vary by age, and that childrens physiology is quite different within the 0-5 years old age range, age-specific cut-points could be useful to accurately classify nonsmoking children as exposed or unexposed to SHS in a standardized manner. This thesis includes the first study estimating age-specific cut-points to classify SHS exposure among children under 5 years old. Interestingly, when applying these serum cotinine cut-points, compared to the assay LOD derived cut-point, results showed that prevalence of childrens SHS exposure declined at all ages, and that concordance between mother-reported SHS exposure and childrens serum cotinine improved considerably.2023-12-1