Exposure to air pollution, especially at school, may be associated with an increased risk of overweight and obesity in childhood, a study by the Institute of Global Health of Barcelona (ISGlobal) suggested. The research included data of 2,660 children between 7 and 10 years old from 39 primary schools in the city of Barcelona.

Previously, some research had already linked exposure to air pollution with an increased risk of childhood overweight and obesity. However, these works are scarce and have focused mainly on exposure to air pollution around the home, without taking into account the school environment.

The study, published in Environment International and carried out in the framework of the BREATHE project, was for the first time to study the risk of obesity and overweight in relation to exposure to air pollution, both at school and in the home, both micro-environments where school children spend more time.

The team collected the weight and height data of the students, calculated their body mass index and the level of overweight or obesity. Then, they measured the contamination of outdoor air in schools. Specifically they measured the levels of nitrogen dioxide (NO2), fine (PM2.5) and ultrafine particles, and elemental carbon (EC). These pollutants were collected with sensors located in the school yards during a week in summer and another in winter. The levels of exposure to NO2, NOx, PM2.5, PM10 and coarse particles (PM-coarse) in the dwellings were also estimated.

We observed that girls and boys exposed to medium or high levels of air pollution –ultrafine particles, NO2, PM2.5 and EC– in schools were more likely to be overweight or obese, compared to those exposed to low levels,” concludes Jeroen de Bont, first author of the study and researcher of ISGlobal and IDIAP Jordi Gol.

At home, exposure to higher levels of PM10 was also associated with more likely to be overweight or obese in childhood, although in this case the analysis was made from estimates of exposure levels.

Limitations of the study

It should be specified that it is a study with limitations, so we must take the results with caution,” explains coordinator of the study Martine Vrijheid, ISGlobal researcher.

Being a cross-sectional research, it only shows data from a specific moment in time, so we do not have enough data to evaluate the nature of the association we have found. In order to draw more solid conclusions, it would be necessary to carry out a new study with a longitudinal approach to follow up on the participants over time,” she adds.

Regarding the mechanism that explains the relationship between air pollution and overweight, some previous studies in animals suggest that “exposure to contamination can induce oxidative stress, insulin resistance and systemic inflammation, factors that are known to contribute to the development of obesity,” de Bont explains.

The majority of children were exposed to levels of air pollution above the World Health Organization (WHO) recommendation, both at home and at school. Specifically, more than 75% were exposed to PM2.5 levels higher than those recommended (10 μg/m3) and more than 50% breathed NO2 levels higher than those considered safe (40μg/m3).