It has long been known that children living in congested cities have higher rates of asthma. All those vehicles, all that pollution. A recent study found that prenatal air pollution exposure is also important in asthma development.
Pregnant women exposed to high levels of tiny ultra-fine particles (UFPs, <0.1 µm) in the air were more likely to have children who developed asthma in the preschool years. Both boys and girls were affected, but high levels seemed to be especially harmful for girl babies exposed late in pregnancy.
Many of the women lived near major roadways with high traffic density - exposure to ultra-fine particles is greater there.
Ultra-fine particles are so small (<0.1 µm) that they can be considered nanoparticles. Their small size makes them so harmful - they can enter the lungs easily and from there travel throughout the body (including the organs), where they cause inflammation and other health effects. Unfortunately, ultra-fine particles are not regulated or routinely monitored in the United States.
From Science Daily: In utero exposure to tiny air pollution particles is linked to asthma in preschoolers
Women who were highly exposed to ultra-fine particles in air pollution during their pregnancy were more likely to have children who developed asthma, according to a study published in the American Journal of Respiratory and Critical Care Medicine in May.
Slightly more than 18 percent of the children born to these mothers developed asthma in their preschool years, compared to 7 percent of children overall in the United States identified as having asthma by the Centers for Disease Control and Prevention.
Other types of pollutants are routinely monitored and regulated to reduce potential health effects, such as larger-size particulate pollution and gaseous pollutants such as nitrogen dioxide. These have been associated with asthma risk in children in prior research. This study controlled for exposure to these other types of pollution and exposure to pollutants following birth, and it still found an elevated risk of asthma in children born to mothers with heightened exposure to ultra-fine particles in pregnancy.
Ultra-fine particulate pollution -- particles that are smaller than the width of an average human hair -- can get deeper into our lungs and pass into our circulation to cause various health effects. Because of this, the researchers said their toxic effects may actually be greater.
This study included 376 mothers and their children, most of them Black or Latinx, who live in the Boston metropolitan area and were already being followed to assess their health. Mount Sinai researchers partnered with a group of scientists at Tufts University in the Boston area who had developed a way to provide valid daily estimations of ultra-fine particulate exposure which could be linked to the area of the mothers' and children's homes. Many of these women were more likely to live near major roadways with higher traffic density where exposure to these tiny particles tends to be higher.
The researchers followed up with the mothers to find out whether the children were diagnosed with asthma. Most of the diagnoses of asthma occurred just after three years of age.
Pollution's effect in utero can alter lung development and respiratory health. This can lead to pediatric disorders like asthma. How this happens is not completely understood but pollution can alter certain bodily regulatory systems like neuroendocrine and immune function that have been linked with asthma in other studies.
While both boys and girls were affected by prenatal ultrafine particle exposure, this study found that girl babies were more sensitive to ultra-fine particle pollution's effects on asthma risk when exposed in late pregnancy. The reason for this phenomenon is also unclear, but studies show it is possibly due to endocrine-disrupting effects of the pollution exposure.