A study conducted in China found that when mothers are exposed to fine inhalable particles (PM2.5), in the form of air pollutants, during the first trimester of pregnancy, it is associated with lower intelligence scores in their children at the age of six. This association was more pronounced in boys, in children who engaged in less outdoor physical activity, and in those who were breastfed for a shorter duration. The study was published in Ecotoxicology and Environmental Safety.
PM2.5, or particulate matter with a diameter of 2.5 micrometers or smaller, consists of tiny particles that are suspended in the air and can be inhaled into the respiratory system. These particles originate from various sources, including combustion processes, vehicle emissions, industrial activities, and natural events like wildfires. They constitute a significant component of air pollution. PM2.5 particles are composed of a mixture of over 50 identified chemical components, with the most common being ammonium, sulfate, nitrate, organic carbon, soil dust, and black carbon.
Due to their small size, PM2.5 particles can bypass the body’s natural defenses and penetrate deep into the lungs, potentially causing or exacerbating respiratory and cardiovascular health issues. The adverse health effects of exposure to PM2.5 include respiratory problems, heart disease, aggravated asthma, and other respiratory or cardiovascular conditions. Studies have indicated that prenatal exposure to PM2.5, especially black carbon, can negatively affect the development of a child’s nervous system by increasing oxidative stress and inflammation.
Xiaowei Sun and her colleagues aimed to investigate the relationship between prenatal exposure to PM2.5 particles and their six main components, and the intelligence levels of children at six years of age. They also examined whether this association was influenced by factors such as the child’s sex, duration of breastfeeding, and level of physical activity. Prior studies suggested that higher levels of physical activity and longer periods of breastfeeding have positive effects on the development of the nervous system. Thus, the researchers hypothesized that these factors might modify the impact of PM2.5 exposure.
The participants in this study were part of the Shanghai-Minhang birth cohort, a longitudinal study that collected information on prenatal exposure to PM2.5 and its primary components. The study included 1292 pregnant women who were recruited during their first prenatal examination between the 12th and 16th week of pregnancy at the Minhang Maternal and Child Health Hospital in 2012. The majority of these women lived in the Minhang, Songjiang, and Xuhui Districts, within 20 kilometers of the hospital. They gave birth to 1225 singleton live babies.
The exposure levels of the participants to PM2.5 particles were estimated using statistical modeling based on satellite measurements of aerosol optical depth. These measurements indicate the concentration and distribution of aerosols in the atmosphere. The researchers cross-validated the satellite data with information from 1000 ground measurement stations. However, precise PM2.5 exposure data was only obtainable for the mothers of 512 children, so the final analyses were based on these results.
To gather data on the mothers and their children, the researchers conducted home visits when the children were 6 months old, and then at 1, 4, and 6 years of age. At the age of 6, children underwent an intelligence assessment using the Wechsler Intelligence Scale for Children, Fourth Edition (WISC-IV). This assessment provided indices of perceptual reasoning, verbal comprehension, and an overall intelligence score. Additionally, data was collected on the parents’ medical history, demographic characteristics, lifestyle factors, pregnancy course, levels of outdoor activity after school, and breastfeeding duration.
The results showed that children whose mothers had lower exposure to PM2.5 particles during the first trimester tended to score higher in perceptual reasoning. Higher maternal exposure levels to ammonium and sulfate particles were associated with lower overall intelligence scores in their children. However, exposure to PM2.5 particles during the second and third trimesters of pregnancy did not show a significant association with the children’s intelligence.
An analysis of the results by gender revealed that the negative associations between maternal exposure to PM2.5 particles and children’s intelligence were primarily observed in boys during the first trimester. For girls, the associations were noticeable with overall PM2.5, ammonium, nitrate, organic carbon, and black carbon exposure during the mothers’ third trimester of pregnancy.
“Exposure of PM2.5 and its five constituents in the first trimester were inversely associated with FSIQ [overall intelligence score] and PRI [perceptual reasoning index] in children aged 6 years, and the adverse effects were more pronounced in boys. More physical activity and longer breastfeeding duration may alleviate the detrimental effects of prenatal PM2.5 and several of its main constituents’ exposure. Our results indicated that prenatal exposure to PM2.5 and its main constituents may disrupt cognitive development in children aged 6 years,” the study authors concluded.
The study makes an important contribution to the scientific knowledge about the effects of air pollution on human health. However, it also has limitations that must be considered. Notably, some participants dropped out during the study, resulting in the final sample being somewhat more educated than the initial sample. Furthermore, the assessment of mothers’ exposure to PM2.5 particles was based on concentrations at their residences during pregnancy, not accounting for exposure at other locations.
The paper, “Prenatal exposure to ambient PM2.5 and its chemical constituents and child intelligence quotient at 6 years of age”, was authored by Xiaowei Sun, Cong Liu, Honglei Ji, Weihua Li, Maohua Miao, Wei Yuan, Zhengwei Yuan, Hong Liang, and Haidong Kan.
