Parental smoking, bronchial reactivity and peak flow variability in children

Background-A systematic quantitative review was conducted of the evidence relating environmental tobacco smoke to bronchial hyperresponsiveness (BHR) during childhood. Methods-Twenty nine relevant studies were identified after consideration of 1593 articles selected by electronic search of the Embase and Medline databases using keywords relevant to passive smoking in children. The search was completed in April 1997. Results-Of 19 studies using challenge tests in children of school age, 10 (5759 children) could be summarised as the odds ratio of being bronchial hyperreactive in children exposed to environmental tobacco smoke compared with those not exposed. The pooled odds ratio for maternal smoking was 1.29 (95% confidence limits 1.10 to 1.50) with no evidence of heterogeneity between studies. However, in five further studies of 3531 children providing some evidence, but not odds ratios, none were statistically significant. A further four studies on 5233 children have collected data but are not published. In contrast, all four studies of circadian variation in peak expiratory flow found increased variation in children exposed to environmental tobacco smoke. Conclusions-A clear effect of exposure to environmental tobacco smoke on BHR in the general population has not been established. While the meta-analysis suggests a small but real increase in BHR in school aged children, it seems likely that this estimate is biased upwards due to publication bias. In contrast, limited evidence suggests greater variation in peak expiratory flow in children of smoking parents.