Environmental Tobacco Smoke Exposure and Respiratory Health in Children: An Updated Critical Review and Analysis of the Epidemiological Literature

Abstract

The issue of environmental tobacco smoke (ETS) exposure of children and respiratory health effects remains a matter of considerable controversy. We undertook to conduct a comprehensive and updated critical review and objective analysis of the epidemiological literature relevant to possible associations between ETS exposure and respiratory health of children. There appears to be a consistent association between parental (primarily maternal) smoking and respiratory symptoms and certain diseases in preschool children (44 reports).On the other hand, there is no consistent association between parental smoking and (1) respiratory symptoms or disease (46 reports); (2) middle ear disease (17 reports), (3) pulmonary function (38 reports), or (4) lung growth and development (5 reports) in school-age or older children. Possible explanations for these data and the age-related differences noted include (1) an ETS effect, with age-dependent variations in susceptibility and/or exposure to ETS;(2) pregnancy and/or lactational effects of maternal active smoking; (3) inaccuracies related to unvalidated clinical data and smoking status misclassification, and (4) variable treatment of socioeconomic status-related and other confounding factors. The available data relative to these issues is inconclusive, and which of these explanations pertain remains to be determined by further research.

Review : Parental Smoking and Middle Ear Disease in Children: A Review of the Evidence

“…In recent years, there has been an increasing awareness of the phenomenon of passive smoking, and in particular, possible adverse effects of smoking by parents on the health of their children. Evidence has been found that children who have been in contact with an active smoker have measurable metabolites of nicotine in their body fluids [41,44,52,69,71,72,77], and that the children of smokers have more respiratory symptoms than the children of non-smokers [61,63,70,96,97]. Reduced auditory function has also been reported in the children of mothers who smoked during pregnancy [23].…”

“…Tobacco smoke may also have an indirect effect via the child's respiratory system, either through a reduction in immune response resulting in more frequent respiratory illnesses [2, 17,19,68,69,73,76,82,94, 98], or through cross-infection from adult smokers who may themselves suffer an increased frequency of respiratory infections [ 17, 19,47,70,73,101,102]. It has been suggested that this second pathway may be a more important cause of respiratory illnesses than a direct effect of tobacco smoke on the child's own respiratory system [19].…”

“…Two explanations were also put forward for the association with maternal smoking during pregnancy which was found by one of the studies. Firstly, early smoke exposure, either transplacentally or through breast-feeding by a mother who smokes, may lead to chronic tubal dysfunction, or sensitise susceptible children to the effects of exposure to other potentially harmful chemicals later in life, thus increasing their chances of developing middle ear problems [41,70]. Hood et al [70] stated that the agedependent association found in the studies they reviewed was consistent with an effect which was not related to ETS exposure, but rather to exposure to smoking by the mother during pregnancy or through breast-feeding, and they felt that such an effect may be stronger than smoking by the parents after pregnancy.…”

“…Most of the studies did not consider the possible effect of maternal smoking during pregnancy, concentrating solely on the child's exposure to smoke after birth. Bearing in mind that women who smoke during pregnancy tend to continue to do so after the birth of their child, separating out the effects of transplacentally-received smoke and exposure to tobacco smoking after birth is very difficult, but if, as Hood et al [70] suggest, smoking during pregnancy is more important than smoking after pregnancy, it could confound the results of the studies which failed to measure this factor and produce spurious associations.…”

“…Before the publication of the Strachan and Cook review, 23 other authors [25, 56, had attempted to summarise the available data on the relationship between childhood middle ear disease and exposure to environmental tobacco smoke (ETS). Eight of these failed to find convincing evidence of a causal association [56,62,68,70,71,74,75,80]. However, the remaining 15 [25, 60, 61, 63-67, 69, 72, 73, 76-79] concluded that there was a causal link, presenting relative risks of between 1.0 and 4.1, depending on the amount smoked per day [60,65,66,76,79], and estimating that exposure to ETS was responsible for between 354,000 and 3.4 million ear-disease-related visits to a doctor's surgery in the US every year [60,63,66].…”