Prenatal Ambient Ultrafine Particle Exposure Tied To Early Childhood Asthma

In utero exposure to ultrafine particles is associated with an increased risk of asthma early in childhood, independent of temperature and exposure to ambient nitrogen dioxide, a study of mothers and children in Boston suggests.

Researchers examined data on 376 mother-child dyads, most of whom were Black (37.8%) or Hispanic (52.9%) and had no more than a high school education (52.9%). By age 3.6 years, 18.4% of the children had asthma based on maternal reports during interviews done every four months from birth to approximately 30 months, then annually.

Based on geocoded data on ambient air pollution exposure at residential addresses, researchers determined that each doubling of the exposure to ultrafine particles (less than 0.1 micrometer) during pregnancy was associated with a significantly higher cumulative asthma risk (odds ratio 4.28).

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"This work should highlight for physicians to take into account environmental factors that can increase risk for the development of asthma starting in pregnancy," said lead study author Dr. Rosalind Wright a professor of pediatrics at the Icahn School of Medicine at Mount Sinai in New York City.

"Thus, obstetricians who care for pregnant women need to be made more aware of factors such as air pollution that can have effects on both moms and their developing baby," Dr. Wright said by email.

While other pollutants in the air have been previously linked to childhood asthma, the current study offers fresh evidence that ambient ultrafine particles may be even more toxic to developing respiratory systems, the study team writes in the American Journal of Respiratory and Critical Care Medicine.

It's possible that enhanced oxidative capacity and the ability to translocate systemically help make ultrafine particles more toxic, but more research is still needed to understand the underlying mechanisms, the researchers note.

Median prenatal ultrafine particle exposure was 27,842 counts/cm2, while median nitrogen dioxide exposure was 31.3 ppb and median temperatures were 11.5 degrees Celsius.

Overall, prenatal exposure to ultrafine particles was more strongly linked to asthma in the first trimester (OR 1.12) and third trimester (OR 1.85) than in the second trimester (OR 1.01).

There were some differences by sex, however. In females, risk of asthma associated with ultrafine particle increased only with exposure in the third trimester (OR 2.71). In males, the risk increase was similar across the first (OR 1.16), second trimester (OR 1.44), and third (OR 1.29) or trimesters.

It's possible that the elevated risk for females late in pregnancy might be due to the endocrine-disrupting effect of ultrafine particle exposure, but more research is needed to confirm this mechanism, the study team notes.

One limitation of the study is the potential for recall bias in maternal-reported asthma, researchers point out. Another limitation is the lack of information on indoor exposure to ultrafine particles, which might influence the outcomes for childhood asthma.

Even so, ultrafine particles have a toxicological profile that indicates this particle size fraction has the potential to have substantial adverse effects in exposed humans, said Dr. Frank Gilliland, a professor at the University of California Keck School of Medicine in Los Angeles, who wasn't involved in the study.

"Because the in utero period is a sensitive developmental period for the immune and respiratory system, maternal exposure to higher levels of ultrafine particles could increase the incidence of childhood asthma," Dr. Gilliland said by email. "Findings from other childhood asthma studies linking asthma occurrence with close residential proximity to busy roads where concentrations are markedly elevated support the conclusion of the current study."

—Lisa Rapaport

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