Air pollution exposure during pregnancy linked with asthma risk

"Our study results highlight the danger of exposure to pollution while babies are still in the womb," said lead author Hind Sbihi, research associate in UBC's School of Population and Public Health. "Air pollution from traffic sources increased the risk of developing asthma during early years before children reach school age, even in an urban area like Vancouver with relatively low levels of air pollution."

Over 65,000 children in Metro Vancouver were included in the study, one of the largest of its kind, and followed from birth until age 10. Researchers monitored physician-diagnosed asthma cases and also assessed the mother's exposure to air pollutants during pregnancy. The measurements focused mainly on traffic-related pollutants, including black carbon, fine particulate matter, nitrogen dioxide, and nitric oxide.

The findings revealed that children whose mothers lived close to highways during pregnancy had a 25 per cent increased relative risk of developing asthma before the age of five.

The risk of developing asthma was associated with increases in the levels of nitrogen dioxide and carbon monoxide found in traffic-related air pollution. Other factors such as low birth weight at term, gestational period, breastfeeding, and socio-economic factors had been controlled for. In addition, they found that children born at low birth weight were more susceptible to the respiratory effects of air pollution.

"We also found that children born to older mothers were at higher risk of being impacted by air pollution exposure. This is particularly relevant in British Columbia, as the province has the highest proportion of mothers giving birth over the age of 35 years old in Canada," said Sbihi.