A groundbreaking study has potentially uncovered a new cause of ADHD in children, finding that exposure to high levels of air pollution and limited access to green space increases the risk of developing the condition.
Performed by researchers at the Barcelona Institute for Global Health (ISGlobal), the study found that children growing up in areas with higher air pollution due to PM2.5 particles and extremely low levels of green space may have up to a 60% increased chance of developing ADHD. The team identified this novel cause of ADHD through examining data of 37,000 children from Vancouver, Canada, providing unprecedented insights into the condition.
The research, which was supported by the La Caixa Foundation, is published in Environmental International
Identifying a new cause of ADHD
The objective of this study was to explore if exposure to air pollution, greenness, and noise in early life could be a cause of ADHD – one of the most prevalent neurodevelopmental disorders that impact between 5-10% of children and adolescents – later in life. In addition, one of the goals was to analyse possible joint effects of these exposures in relation to ADHD.
For their investigation, the team employed administrative data of births in Metro Vancouver between 2000 and 2001, identifying ADHD cases from hospital cases, physician visits and prescriptions. They estimated the levels of green space in the participants’ neighbourhoods with an accurate satellite metric. Moreover, residential levels of the air pollutants NO2 and PM2.5 and noise levels were determined using available exposure models. Potential associations between the environmental exposures and ADHD were assessed using a statistic model that effectively determines hazard ratios.
From this, the researchers found 1,217 ADHD cases, equating to 4.2% of the total study population. Examining green space illuminated that living in areas with a higher percentage of vegetation had a lower risk of ADHD, finding that a 12% increase in vegetation percentage was associated with a 10% reduction in ADHD risk.
In terms of air pollution, individuals with higher exposure to fine particles had a higher risk of ADHD – every 2.1 µg increase in the levels of PM2.5was linked to an 11% increase in the risk of ADHD. The team found no associations for the rest of the environmental exposures of NO2 and noise.
Joint exposure effects
The team’s research builds on previous findings from studies that identified associations between green space and air pollution. However, the majority of the research conducted until this study focused on the evaluation of single exposures and rarely evaluated joint effects of multiple environmental exposures as a potential cause of ADHD.
Matilda van den Bosch, the leader of the research from ISGlobal, commented: “We observed that children living in greener neighbourhoods with low air pollution had a substantially decreased risk of ADHD. This is an environmental inequality where, in turn, those children living in areas with higher pollution and less greenness face a disproportionally greater risk. These associations are particularly relevant because exposures take place in early life, a crucial period for brain development where children are especially vulnerable. Importantly, these exposures are modifiable, meaning that the findings should be taken into account for healthier urban planning.”
“Our findings also show that the associations between PM2.5 and ADHD were attenuated by residential green space and vice versa as if the beneficial effects of vegetation and the harmful effects of PM2.5 neutralised each other,” said Weiran Yuchi, a researcher at the University of British Columbia (Canada) and first author of the study.