Prenatal, postnatal exposure to air pollution increases risk for asthma, wheeze

High levels of exposure to fine particulate matter during specific prenatal and postnatal developmental windows may increase the risk for childhood asthma and wheezing, according to a study published in Pediatric Allergy and Immunology.

Targeted measures to reduce exposure to these pollutants are needed to lower these risks, Guimin Chen, of the School of Public Health at Southern Medical University in Guangzhou, China, and colleagues wrote.

The Prospective Birth Cohort Study on Prenatal Environments and Offspring Health recruited pregnant women between January 2016 and December 2017 in Guangzhou, China, who gave birth to 3,725 children.

Between January 2016 and July 2020, 10.52% of these children (mean age, 3.2 years ± 0.8 years) were diagnosed with asthma and wheezing. These children tended to be boys, and their mothers likely had large parity, used artificial feeding and consumed fewer vitamins.

Median concentrations of fine particulate matter at the 2.5 µm scale (PM_2.5) totaled 31.9 µg/m³ during pregnancy and 31.1 µg/m³ during childhood.

Average PM_2.5 concentrations significantly correlated with ozone (O₃, Pearson correlation coefficient [r] = 0.16), sulfur dioxide (SO₂, r = 0.4), nitrous oxide (NO₂, r = 0.66) and carbon dioxide (CO, r = 0.54) during pregnancy. Similarly, average PM_2.5 concentrations correlated with O₃ (r = –0.42), SO₂ (r = 0.81), NO₂ (r = 0.77) and CO (r = 0.66) during childhood.

According to the researchers, there was a 1.44 adjusted HR (95% CI, 1.13-1.85) for asthma and wheezing for each interquartile range (IQR, 4.8 µg/m³) increment in PM_2.5 concentration during the entire pregnancy.

The researchers said they found similar effects from PM_2.5 exposures during the pseudoglandular stage between 5 and 16 gestational weeks (IQR, 4.8 µg/m³; HR = 1.1; 95% CI, 1.02-1.18) and canalicular stage between 16 and 24 gestational weeks (IQR, 4.8 µg/m³; HR = 1.13; 95% CI = 1.03-1.23) on risks for asthma and wheezing.

During childhood, the researchers found adjusted HRs for asthma and wheezing for each IQR increment in PM_2.5 concentrations (IQR, 1.5 µg/m³) of 2.74 (95% CI, 2.59-2.91) in the first year, 1.57 (95% CI, 1.43-1.73) in the second year, 2.37 (95% CI, 2.24-2.51) in the third year and 2.27 (95% CI, 2.18-2.37) in the year before the end of the follow-up.

The researchers suggested that developing lungs may be more susceptible to PM_2.5 exposure during the pseudoglandular and canalicular periods, leading to asthma and wheeze. The tracheobronchus continues to elongate between 5 and 16 gestational weeks, they wrote, while cartilage, smooth muscle and connective tissue differentiate from the stroma. Then, respiratory bronchioles develop after 16 weeks’ gestation.

Also, the researchers found that more than 85% of alveolarization takes place after birth, with the lung developing fastest within the first 3 to 4 years. When the immature immune system, higher ventilation rates and increased lung surface area per kg of body weight also are considered, the researchers found, children at these ages are especially vulnerable to air pollution.

With these findings, clinical workers and pregnant women could better understand the adverse effects of PM_2.5 on the respiratory system and reduce exposure to air pollution during periods of more susceptibility, according to the researchers.

These findings also could be used to inform public policy, the researchers continued, to prevent asthma by improving air quality.