Objective: To determine the effects of prenatal and postnatal smoke exposure on the respiratory health of children in the United States.
Design: Nationally representative cross-sectional survey, including questionnaire information, measurements of serum cotinine (a metabolite of nicotine), and pulmonary function measurement, of 5400 US children.
Setting and participants: Children aged 4 to 16 years in the Third National Health and Nutrition Examination Survey, October 25, 1988, to October 15, 1994.
Methods: We stratified the study participants into tertiles, on the basis of serum cotinine levels, and used logistic and linear regression modeling, adjusting for known covariates, to determine the effect of high environmental tobacco smoke (ETS) exposure (on the basis of a high cotinine level) on outcomes such as the prevalence of current asthma, the prevalence of frequent wheezing, school absence, and lung function. For children aged 4 to 11 years, we also determined the effect of prenatal maternal smoking on these outcomes.
Results: We observed effects of ETS exposure in all age groups, although the effects varied between age groups. Among all children significant effects associated with high cotinine levels were for wheezing apart from cold in the past year (odds ratio [OR], 1.8; 95% confidence interval [CI], 1.1-2.8); 6 or more days of school absence in the past year (OR, 2.0; 95% CI, 1.4-2.8); and lung function decrements in the forced expiratory volume in 1 second (mean change, -1.8%; 95% CI, -3.2% to -0.4%) and the maximal midexpiratory flow (mean change, -5.9%; 95% CI, -8.1% to -3.4%). Although current and ever asthma were not significantly associated with high cotinine levels in the overall group (OR, 1.5; 95% CI, 0.8-2.7, and OR, 1.3; 95% CI, 0.8-2.2, respectively), they were increased significantly among 4- to 6-year-old children (OR, 5.3; 95% CI, 2.2-12.7, and OR, 2.3; 95% CI, 1.1-5.1, respectively).
Conclusions: We investigated recent ETS exposures as important predictors of respiratory health outcomes in children 4 years and older. Environmental tobacco smoke exposure affects children of all ages, although the exact effects may vary between age groups.