In-utero exposure to poor air quality a risk factor for childhood ADHD

Children born to mothers who were exposed to polluted air while pregnant are at increased risk of childhood attention-deficit hyperactivity disorder (ADHD), according to a study presented at PAS 2023.

In the Boston Birth Cohort, trimester-specific and whole-pregnancy exposure to fine particulate matter (PM_2.5) had a significant dose-response relationship with the risk of ADHD in offspring (trend p<0.001), reported one of the study investigators Mengmeng Li, senior data analyst of the Global Early Adolescent Health Project at Johns Hopkins Bloomberg School of Public Health, Cheltenham, Pennsylvania, US. 

Furthermore, the risk of childhood ADHD was heightened if mothers with the highest quartile of PM_2.5 exposure also smoked cigarettes (relative risk [RR], 2.16, 95 percent confidence interval [CI], 1.54–3.03) or were highly stressed (RR, 2.03, 95 percent CI, 1.42–2.92), as Li pointed out.

“The population attributable risk estimated a 23-percent reduction in ADHD if whole-pregnancy PM_2.5  exposure were eliminated,” she said.

The Boston Birth Cohort included 2,932 children, of which 445 had ADHD (72 percent boys). Compared to mothers of children without ADHD, mothers of children with ADHD tended to be born in the US (51 percent vs 37 percent), be unmarried (74 percent vs 65 percent), and have smoked cigarettes (35 percent vs 24 percent). [Li M, et al, Pediatric Academic Societies Annual Meeting 2023]

“Our main findings remained robust when further controlled for substance use, diet, placental inflammation, preterm birth, and neighbourhood equity index,” Li noted.

Broad health impact

Poor air quality has long been associated with a wide spectrum of adverse health outcomes, such as incapacitating the pulmonary, cardiovascular, and central nervous systems. [Int J Environ Res Public Health 2022;19:14019; Circulation 2019;139:1766-1775; Hypertension 2018;72:194-201; Environ Res 2022;209:112895]

Researchers think that ambient particulate matter with an aerodynamic diameter ≤2.5 micrometres can penetrate and lodge itself deeply into the lungs and then diffuse into systematic circulation. This can lead to neurodegenerative diseases and increased child morbidities. [Sci Total Environ 2017;592:451-457; Sci Total Environ 2019;655:1240-1248; Am J Epidemiol 2014;180:359-366; JAMA Netw Open 2019;2:e1917643; Diabetologia 2013;56:1696-1704]

“The in-utero period is a critical window for brain development vulnerable to environmental insults,” according to Li. “If further replicated, our study findings have important environmental health and policy implications.”

Li called out the inadequacy of current PM_2.5 standard to protect low-income mother-children pairs residing in urban areas from social-environmental risk factors during the sensitive early-life development stage. Stressing the importance of having adequate protection, Li pointed out that ADHD is a common childhood neurodevelopmental condition, which is highly prevalent among Black (12 percent) and Non-Hispanic White (10 percent) children and adolescents, and can persist into adulthood with potential life course consequences.

“Consideration of short-term and long-term impacts of prenatal exposure in policy update and reinforcement [should be taken into account],” she said.