Prenatal air pollution exposure linked to higher childhood obesity risk

Exposure to air pollution during pregnancy, specifically to fine particulate matter (PM_2.5), may increase the risk of childhood overweight or obesity. This is the conclusion of a large, pan-European meta-analysis study led by the Barcelona Institute for Global Health (ISGlobal), a center supported by the "la Caixa" Foundation, and recently published in Environment International. The study examined the relationship between exposure to air pollutants during pregnancy and during childhood, and its impact on body mass index (BMI) and the risk of overweight or obesity throughout childhood.

The study is part of the LifeCycle and ATHLETE projects, funded by the European Union, with the aim to evaluate how early life environmental stressors affect health over time. For this research, data were collected from mothers and children from 10 birth cohorts in 8 European countries. In total, 37,111 mother-child pairs participated during the prenatal period and 33,860 during the childhood stage.

The research team calculated pregnancy and annual average concentrations of nitrogen dioxide (NO_₂) and fine particulate matter (PM_2.5) at the family's place of residence using geospatial models. The study covered air pollution exposures from pregnancy until the children reached 12 years of age. Children's height, weight and age were obtained through clinical assessments or parental reports, and used to calculate BMI. Then, cohort-specific associations between air pollution exposure and childhood obesity outcomes were estimated and pooled together in a meta-analysis of all cohorts.

Higher risk of overweight or obesity in childhood

Exposure to higher levels of PM_2.5 during pregnancy was associated with a 23% increased risk of childhood overweight or obesity. This association was strongest in the 9–12 year age group. However, the study did not observe any associations with exposure to PM_2.5 during childhood, nor with NO_₂ exposure during pregnancy or childhood.

Our results indicate that the gestational period may represent a particularly vulnerable window for the risk of childhood obesity. However, further research is needed to precisely identify the critical periods during which exposure to air pollution might influence this risk, and to confirm these findings."

Sarah Warkentin, ISGlobal researcher and first author of the study

"The biological mechanisms that may explain the relationship between exposure to air pollution and weight gain in children are not yet fully understood. In previous studies, exposure to pollution during pregnancy has been linked to reduced fetal growth and low birth weight. This may be due to oxidative stress, inflammation, problems in placental development, or hormonal disruptions. These same processes could also affect growth and increase the risk of obesity during childhood, as shown in animal studies," explains Martine Vrijheid, director of ISGlobal's Environment and Health over the Lifecourse programme and senior author of the study.

Heterogeneity among cohorts

The results showed that the associations between air pollutants and childhood obesity outcomes differed substantially between the different cohorts. For instance, prenatal and postnatal exposure to PM_2.5 was associated with a lower BMI at all ages in UK cohorts, whereas childhood exposure to PM_2.5 and NO_₂ was associated with a higher BMI in a Dutch cohort.

"This heterogeneity could be due to varying levels of air pollution exposure among the cohorts, possible differences in children's lifestyle habits in each country, which could influence their exposure to air pollution and, in turn, their weight, as well as other factors specific to each city's environment," says Martine Vrijheid.