Traffic-Related Air Pollution Linked to Childhood Asthma Development

A 2016 international study suggested that increased exposure to traffic-related air pollution (TRAP) might play a significant role in the increased prevalence of childhood asthma since the 1950s.

Interdisciplinary researchers from the University of Leeds, in the United Kingdom, the University of Pompeu Fabra and the Barcelona Institute for Global Health and Centre for Research in Environmental Epidemiology (ISGLOBAL-CREAL) in Barcelona, Spain, and the Consortium of Biomedical Research in Epidemiology and Public Health (CIBER ESP) in Madrid, Spain led by Haneen Khreis, MSc, PhD, from the University of Leeds Institute for Transport Studies, focused on early-life exposure to TRAP and increased risk of asthma incidence and exacerbation.

Khreis explained that although many early reviews have "effectively excluded ambient air pollution as a plausible cause of the rise in asthma incidence," their analysis proved that positive correlations existed between TARP exposure and the "incidence and prevalence of asthma" in children from birth to 18 years of age.

Khreis remarked that ambient air pollution has a different chemical and physical make up to TARP, and argued that studying the relationship between TARP exposure and asthma is crucial for understanding environmental factors that could impact asthma development.

The study argued that "early-life and childhood could represent critical exposure windows for asthma development due to the plasticity and susceptibility of target organs and systems during these developmental periods." Understanding the effects of TARP exposure on childhood asthma development may help to guide environmental researchers and healthcare providers in curtailing the rise of childhood asthma in increasingly dense urban environments worldwide.

Khreis and fellow researchers used data from epidemiological/observational studies, which "explicitly specified the term 'asthma' as an outcome for investigation," examined childhood exposure "from birth until 18 year old to any designated TRAP metric," or "examined and reported associations between preceding exposure to TRAP and subsequent risk of asthma reported as incidence or lifetime prevalence from birth to 18 years old."

Data from the studies were then extracted and validity was assessed using Critical Appraisal Skills Program procedures and an additional six parameters selected to evaluate the potential for bias in the studies and determine special characteristics, which might limit the studies.

The final meta-analysis included data from over 40 articles published between 1999 and 2016, and showed that there were significant increased overall-risks estimates for asthma development after exposure to TARP and risk increases associated with specific TARP chemicals for both younger (below 6) and older (6-18) children. The study also analyzed the individual effects of specific TARP elements, such as black carbon concentrations, particulate matter, nitrogen dioxide, and nitric oxide, discovering consistent evidence that early childhood (under age 6) exposure to these elements correlates with a significantly higher risk estimate for asthma susceptibility, and that risk remained significant, but lessened, with later childhood exposure (ages 6-18).

Khreis and her fellow researchers concluded that based on their study there is "sufficient evidence to support an association between the exposure to TRAP and the development of childhood asthma" particularly among children exposed in early-childhood.

The group suggested that further studies might determine the degree with which continued exposure, exposure to specific pollutants found in TARP, and age-range might contribute to heightened risk factor and susceptibility.

The article, "Exposure to traffic-related air pollution and risk of development of childhood asthma: A systematic review and meta-analysis" was published in the March 2017 issue of Environment International.

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