Increased Risk of Asthma Development Linked to Ozone Exposure at Birth

Teresa To, PhD, senior scientist, child health evaluative services, Hospital for Sick Children

Teresa To, PhD

A long-term study, a 10-year follow-up to the 2006 Toronto Child Health Evaluation Questionnaire (T-CHEQ), has found that exposure to ozone (O₃) at birth was associated with an increased risk of incident asthma, allergic rhinitis and eczema.

The study, presented at the 2018 American Thoracic Society International Conference, suggests that improving air quality and increasing awareness about the risks of air pollution may have beneficial effects on the prevention of asthma and other allergic diseases.

“Our findings show that the hazard ratios for ozone measured at birth as a single pollutant showed statistically significant higher risks for development of asthma, allergic rhinitis and eczema,” lead author Teresa To, Phd, senior scientist, child health evaluative services, The Hospital for Sick Children (SickKids), said. “The results of our study are important because the study examines the effect of population on health outcomes in early childhood, and has the longest longitudinal follow-up of a cohort of school-aged children in Canada.”

In the follow-up study, researchers observed associations between ambient nitrogen dioxide (NO₂) and O₃ exposures at birth and incidence of asthma, allergic rhinitis and eczema in childhood through adolescence.

The cohort followed 1881 children (48% boys) from birth for an average of 13 years. Amongst the children, 31% developed asthma, with an average age of 3 years at incidence, 42% had allergic rhinitis and 76% had eczema.

A 10-unit increase in exposure to O₃ at birth was associated with an 82% increased hazard of asthma (HR: 1.82, 95% CI: 1.05, 3.18), while exposure to NO₂ was not associated with asthma (HR: 1.02, 95%CI: 0.53, 1.98).

For both allergic rhinitis and eczema, a 10-unit increase in O₃ was associated with increased hazard of disease, while NO₂ was not associated. A similar risk was not observed in association with exposure to PM_2.5.

Researchers collected average annual concentrations of pollutants from fixed monitoring stations across Ontario and assigned these measures based on study participant’s postal codes at birth.

Development of allergic diseases were determined based on health service records used for the conditions; researchers adjusted for variables like parental history of asthma and early home exposure to pollutants.

To conclude, in Ontario, ambient air exposure to O_3, but not NO₂ was associated with a greater risk of incident asthma, allergic rhinitis and eczema.

These findings have significant implications for other countries with higher levels of pollution.

“Air pollution isn’t only one or a few countries’ problems, but rather a global public health concern,” To concluded. “While there are individual actions one can consider to reduce exposure to air pollutants, it also requires action by public authorities at the national, regional and international levels. Reducing air pollution could save millions of lives.”

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