Purpose of the Study. Asthma is becoming more prevalent in the industrialized regions of the world. The rapid rise in childhood asthma suggests an environmental etiology. In this study, the authors evaluate the effects of maternal smoking during pregnancy and childhood environmental tobacco smoking (ETS) exposure on asthma and wheezing in school-aged children in southern California.
Methods. Self-administered questionnaires were sent to parents of 4th, 7th, and 10th grade students in 12 southern California communities. The responses to 5762 of these questionnaires completed by parents were used to ascertain children with wheezing or physician-diagnosed asthma and to gather information on lifetime household exposures to tobacco smoke and history of maternal smoking during pregnancy. Logistic regression models were fitted to cross-sectional data to estimate the effect of in utero exposure to maternal smoking and previous and current household exposure to tobacco smoke on the prevalence of wheezing and physician-diagnosed asthma.
Results. In utero exposure to any maternal smoking without subsequent postnatal environmental tobacco smoking exposure was associated with increased prevalence of physician-diagnosed asthma (odds ratio [OR]: 1.8), asthma with current symptoms (OR: 2.3), asthma requiring medication use in the previous 12 months (OR: 2.1), lifetime history of wheezing (OR: 1.8), current wheezing with colds (OR: 2.1) and without colds (OR: 2.5), persistent wheezing (OR: 3.1), wheezing with exercise (OR: 2.4), attacks of wheezing causing shortness of breath (OR: 2.4) or awakening at night in the previous 12 months (OR: 3.2), and wheezing requiring medication (OR: 2.1), or emergency room visit(s) during previous year (OR: 3.4).
Current and previous ETS exposure was not associated with asthma prevalence, but was associated with subcategories of wheezing. Current ETS exposure was associated with lifetime wheezing (OR: 1.3), current wheezing with colds (OR: 1.6) and without colds (OR: 1.5), wheezing with exercise (OR: 1.7), attacks of wheezing causing shortness of breath (OR: 1.6) or awakening at night (OR: 1.5), and wheezing requiring medication (OR: 1.4), or emergency room visit(s) in the previous year (OR: 1.9). The effect of current ETS exposure on subcategories of wheezing were most pronounced among children exposed to 2 or more smokers.
Conclusions. Authors conclude that in utero exposure to smoking increases the risk of physician-diagnosed asthma and wheezing during childhood. However, current ETS exposure is associated with wheezing, but not physician-diagnosed asthma. The authors further hypothesized that ETS acts as a cofactor with other insults such as recurrent infections as a trigger of wheezing attacks, rather than as a factor that induces asthma.
Reviewers’ Comments. This was a large study involving 5672 school-aged children in 12 different communities in southern California. The most striking finding in this study is the association between in utero exposure to tobacco smoke alone and childhood physician-diagnosed asthma. This is consistent with growing evidence that in utero exposure to tobacco smoke increases the risk of abnormal lung function at birth and in childhood, bronchial hyperactivity, wheezing, and asthma in childhood. The results suggest that in utero exposure to tobacco smoke may alter critical developmental pathways of the lung predisposing these children to wheezing and asthma. ETS also appears to be important in childhood wheezing (probably asthma), but less significant compared with in utero exposure.
The main limitation of this study results from the use of questionnaires and reliance on the retrospective recall of parents for data collection. Exposure to tobacco smoking was assessed through questionnaire responses and not validated by more objective measurements such as cotinine levels. The study lacks information on the actual duration and intensity of exposure to tobacco smoke, because children and parents may have altered their time-activity pattern to avoid exposure to tobacco smoke. The study also lacks information on confounding factors such as maternal nutritional status and alcohol or other toxic substance intake during pregnancy. Although one can also argue that questionnaire data collections are prone to errors in reporting, given the stigma associated with smoking, parents are more likely to underreport and bias the data toward the null hypothesis.
- Copyright © 2002 by the American Academy of Pediatrics