Does traffic related air pollution cause childhood asthma

Session: New perspectives on vulnerable groups

Does traffic-related air pollution cause childhood asthma?

Haneen Khreis1, Charlotte Kelly1,2, James Tate1, Roger Parslow3 and Karen Lucas1

1 Institute for Transport Studies, 2 Leeds Institute of Health Sciences, 3 Leeds Institute of Cardiovascular and Metabolic Medicine, University of Leeds

Changing Perspectives: 1st International Conference on Transport and Health, London, 6 – 8 July 2015

50 years of asthma: UK trends from 1955 to 2004

Trends in the prevalence of a diagnosis of asthma ever in children. m, month; y, year. Source: Anderson et al. (2007)

Why such steady and rapid increases?

“… the increase in disease must be attributable to a change in as-yet unknown environmental factors… ” (Cookson, 2004, p. 979)

Source: Brook (2012)

Does children’s exposure to traffic-related air

pollution increase their risks of developing

asthma?

Meta-analysis

Case study - The Born in Bradford

Systematic review

Provide data

Learn and apply lessons

Does children’s exposure to traffic-related air pollution increase their risks of

developing asthma?

3. Include studies which investigate children’s exposure to traffic-related air pollution only1. Include human

studies only 2. and children’s studies only 4. Include studies which investigate exposure to

traffic-related air pollution or traffic-related air pollutants when road traffic is specified as their source

6. Include studies which specifically investigate the subsequent risk of asthma development in childhood

7. Include observational studies only

5. Include studies which report measures of

association and their confidence interval precision

Khreis et al. (2014). Exposure to traffic-related air pollution and the development of childhood asthma. PROSPERO 2014:CRD42014015448, available from: http://www.crd.york.ac.uk/PROSPERO/display_record.asp?ID=CRD42014015448

http://www.crd.york.ac.uk/PROSPERO/display_record.asp?ID=CRD42014015448

Screening process

Research gaps and impact on validity: asthma definitions

• Heterogeneous disease • No universally accepted

definition• Has many phenotypes• AND non-specific symptoms….


Self-report of doctor-diagnosis = 12.0%

Hospitalization registry = 6.6%

Prescription registry = 32.2%

Source: Hansen et al. (2012)


Self-report of doctor-diagnosis = 12.0%

Hospitalization registry = 6.6%

Prescription registry = 32.2%

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12

Source: Hansen et al. (2012)

Research gaps and impact on validity: exposure models

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Fay D, Tate J, Khreis H (2015): Investigating pedestrians PNC exposures in urban micro-environments near a busy road traffic intersection


Proximity to roadways

Regulatory monitoring stations

Land-use regression models

Dispersion models


10 studies reporting 30 risk estimates, 53% were positive (31% significant)




23 studies, 153 main risk estimates from 4 exposure models, 114 (75%) positive, 45 (39%) statistically significant… and more from the other exposure models…

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So does traffic-related air pollution cause asthma?

“The results found across the studies followed a pattern that would be expected under the plausible assumption that the pollutants really are causally associated with asthma development, if only among a subset of children…”

(HEI, 2010, p.363)

But…

Which pollutant(s)…

But…

… and why this heterogeneity? • Differences in study

designs, populations, exposure models, outcome definitions and confounders selection• Certain susceptibility

factors may be one reason (early life exposures, sex)• Only certain phenotypes of

asthma may be affected?

• Traffic-related air pollution might have contributed to the recent asthma epidemic• Effect estimates are very likely to

have been distorted/ underestimated• Many effects were detected in areas

meeting the relevant air quality guidelines • Black Carbon (and ultra-fine particles)

are yet unregulated

Implications

• Traffic-related air pollution is a modifiable environmental factor• Black Carbon (and ultra-fine particles)

are truly traffic-related pollutants• -28% / -40% decreases in Black

Carbon in the Milan congestion charging area (Mattioli, 2014)

• A substantial proportion of asthma cases can be prevented?

Implications

Thank you!

References

• Anderson, H. R., Gupta, R., Strachan, D. P., & Limb, E. S. (2007). 50 years of asthma: UK trends from 1955 to 2004. Thorax, 62(1), 85-90.

• Brook, J. R. (2012) 'Estimating exposure to traffic-related air pollution', in Health Effects Institute Annual Conference, Chicago, Illinois, 15-17th April 2012.

• Cookson, W. (2004). The immunogenetics of asthma and eczema: a new focus on the epithelium. Nature Reviews Immunology, 4(12), 978-988.

• Hansen, S., Strom, M., Maslova, E., Mortensen, E. L., Granstrom, C., & Olsen, S. F. (2012). A comparison of three methods to measure asthma in epidemiologic studies: results from the Danish National Birth Cohort. PloS one, 7(5), e36328.

• Health Effects Institute, H. E. I. (2010) Traffic-related air pollution: a critical review of the literature on emissions, exposure, and health effects, Health Effects Institute.

• Khreis H, Kelly C, Tate J, Parslow R (2014). Exposure to traffic-related air pollution and the development of childhood asthma. PROSPERO :CRD42014015448, available from: http://www.crd.york.ac.uk/PROSPERO/display_record.asp?ID=CRD42014015448

• Mattioli, G. (2015). Pollution or congestion charging? Air quality measures and road pricing in Milan, Italy, in Institute for Transport Studies Research Seminar Series, University of Leeds, 05 March 2015.

Does traffic related air pollution cause childhood asthma

Health & Medicine

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