Saturday, 19 January 2013

A dangerous cocktail brews in our towns and cities- How tobacco smoke and vehicular emissions together contribute to wheezing in young children

Vehicular emissions and tobacco smoke are harming the lungs of young children  in our cities

When it comes to the evidence against tobacco and vehicular emissions on harming human respiratory health, it does not rain but it pours. And it keeps on coming. We have extensive evidence to show that vehicular emissions as well as tobacco smoke exposure are bad for health and it seems to start right from the fetal stage.  A new study presented in the journal Environmental Health shows that exposure to traffic-related air pollutants is associated with increased risks of wheezing in children who are exposed to tobacco smoke in fetal  life and infancy indicating an axis of villains who co-operate to exert their  harmful effects.

The study was a large prospective cohort study involving 4,634 children in Rotterdam, the second largest city in the Netherlands.  One of the largest ports in the world, it is also one of the most polluted places in the Netherlands and an apt location for pollution studies. A prospective cohort study is one that monitors a group of similar individuals –cohorts- who differ in certain factors under study over a time period in order to understand how these factors affect rates of a certain outcome- in this study, how effects of vehicular emissions, tobacco smoke exposure (in any stage starting from fetal life to the age of 3 years) affect wheezing in children.

Many cities, like this one, has air pollution monitors that helps scientist understand how air pollutants affect human health .
 Particulate matter (PM) of the size of 10 microns or less can penetrate the deepest part of the lungs such as the bronchioles or alveoli. Domestic coal combustion was once the major source of particulate emissions, but recently other sources such as road transport are important sources with diesel vehicles notably emitting increased levels. Road vehicle exhausts, off road equipment, and power plants  are  important sources of NO2.  In addition to contributing to the formation of ground-level ozone, and fine particle pollution, NO2 is linked with a number of adverse effects on the respiratory system. In this study, the exposure of children to particulate matter (PM10) and nitrogen dioxide (NO2) were assessed by analysing emission data at the home address. Parents were asked to fill questionnaires that indicated whether their children had wheezing until the age of 3 years.  Parents were also asked to provide information on whether the fetus or the baby had been exposed to tobacco smoke either through the mother or the partner smoking tobacco.

Results from the study indicated that average annual PM10 or NO2 exposure levels per year were not associated with wheezing in the same year.  Even though there were trends showing a link with PM10 or NO2 exposure levels and wheezing during the first 3 years of life, the results were not statistically significant. The researchers did not observe associations of traffic-related air pollutants with wheezing among children who were exposed to smoke during fetal life only or during infancy only. But in children who were exposed to tobacco smoke in both fetal and infant stage, PM10 or NO2 exposure levels was associated with wheezing during the first 3 years of life. The scientists did not observe associations of traffic-related air pollutants with wheezing among children who were not exposed to tobacco smoke.

There are limitations in the study, one of  which the researchers have noted viz. the possibility of ‘misclassification of air pollution assessment’ owing to the analysis only  involving  exposure levels at home addresses and not at the day care centers or other places where the child may spend days and nights. One factor that could have further added value to the study is blatantly missing- work addresses of mothers and PM 10, NO2 levels  - and whether when analysed together with air pollution exposure at home had any links to wheezing in children.

Nevertheless the study extends our understanding on how air pollution and tobacco smoke exposure contribute to the health of younger children. The  results suggest that long term exposure to traffic-related air pollutants is associated with increased risks of wheezing in children exposed to tobacco smoke in fetal life and infancy. Tobacco smoke exposure in early life might lead to increased vulnerability of the lungs to air pollution. The evidence appears to show that exposure of fetus and  infant lung to tobacco smoke primes it for damage by air pollutants leading to wheezing suggesting that the dangerous cocktail is made more potent by the ingredients together.


Sonnenschein-van der Voort, A., de Kluizenaar, Y., Jaddoe, V., Gabriele, C., Raat, H., Moll, H., Hofman, A., Pierik, F., Miedema, H., de Jongste, J., & Duijts, L. (2012). Air pollution, fetal and infant tobacco smoke exposure, and wheezing in preschool children: a population-based prospective birth cohort Environmental Health, 11 (1) DOI: 10.1186/1476-069X-11-91

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