Early rather than recent exposure to tobacco increases bronchial reactivity

Background: Tobacco is well known to impair respiratory function of infants and children. This study was done to identify periods of increased vulnerability of the airways to tobacco products. Patients and methods: In 162 unselected schoolchildren maximum expiratory flow at 25 % of vital capacity (MEF25) was measured before and after cold air hyperventilation. Parental smoking habits were assessed by measurement of cotinine concentrations in children's urine and by interview. Results: Children, whose mothers had smoked during pregnancy, showed increased bronchial reactivity at school age compared to children whose mothers had not smoked during pregnancy (median MEF25 [25th, 75th percentile] after cold air challenge as percent of baseline: 83 % [76, 95] vs. 95 % [79, 100]; p = 0.03). Similar differences were found, when the study population was divided according to the maternal smoking status during the first six months of life. On the contrary, if the cotinine excretion exceeded the group median as a measure of recent exposure to tobacco smoke, bronchial reactivity was not increased (median MEF25 [25th, 75th percentile] as percent of baseline: 88% [76, 100) vs. 93 % [79, 100]: p = 0.25). Conclusions: Pregnancy and early infancy were found to be periods of increased vulnerability of the airways to tobacco products.