Study Reveals Exposure to Air Pollution Contributes to Childhood Asthma

Results from a new study performed in Ontario have illustrated that children born in Sarnia have a greater risk of developing asthma than those in neighboring cities.

A group of researchers from Lawson Health Research Institute and Western University used provincial data from ICES and discovered that greater air pollution exposure in the first year of life very probably contributed to this greater risk. The findings were reported recently in the journal CMAJ Open.

Summary of Study Results

• Children who were born in Sarnia in the 1990s and early 2000s were disproportionally at a greater risk of developing asthma in the first few years than those in the neighboring cities.
• In the first year, air pollution exposure was identified to be related to the development of asthma in children.
• In Southwestern Ontario, overall rates of new childhood asthma diagnosis have been reducing over time along with decreases in the levels of air pollution.

It’s known that cities in Southwestern Ontario have varied levels of air pollution because of differences in industry and traffic. For example, Sarnia is home to the ‘Chemical Valley’ where numerous chemical plants and oil refineries are clustered.

Dr Dhenuka Radhakrishnan, Adjunct ICES Scientist and Pediatric Respirologist, Children’s Hospital of Eastern Ontario

“We wanted to see if children born in three cities—London, Windsor and Sarnia—had a different risk of developing asthma due to the differing air pollution levels in the three regions, even though the people living in these cities are otherwise comparable in many ways,” added Dr Radhakrishnan.

Dr Radhakrishnan was formerly working out of ICES Western in London.

The team tracked 114,427 children who were born in these cities between 1993 and 2009 for 10 years and discovered that those in Sarnia were at a greater risk of developing asthma. They identified that by the age of 10, almost 24% of children in Sarnia were diagnosed with asthma, when compared to 17% in London and 21% in Windsor.

Moreover, the variations were present after accounting for several risk factors related to asthma, like sex, urban versus rural setting, and socioeconomic status. The study results were most obvious in the first two years of life, but steady over the age of six.

“Reassuringly, we found the asthma risk for children has reduced in more recent years as pollution levels have also decreased,” added Dr Radhakrishnan.

Asthma is the most general chronic disease found in Canadian children and has a considerable effect on the quality of life. Asthma is the chief cause for people making emergency department visits and hospital admissions in this age group.

It’s important to find strategies to prevent asthma development and this study suggests that reducing air pollution exposure, including environmental causes, might reduce the number of children who suffer from asthma.

Dr Salimah Shariff, Associate Scientist, Lawson Health Research Institute

Shariff is also an adjunct professor at Western and a scientist at ICES Western.

Moreover, there is increasing proof that exposure at the time of pregnancy can impact the development of asthma in children.

We need to carefully examine how reducing air pollution exposures within a geographic area translates to reductions in asthma development. Understanding the amount of air pollution that a mother and infant are exposed to, and how this impacts their personal risk, could enable regions to target safer levels for their residents.

Dr Salimah Shariff, Associate Scientist, Lawson Health Research Institute

Video Credit: Lawson Health Research Institute.

Journal Reference:

Radhakrishnan, D., et al. (2021) Comparison of childhood asthma incidence in 3 neighboring cities in southwestern Ontario: a 25-year longitudinal cohort study. CMAJ Open. doi.org/10.9778/cmajo.20200130.