adhd risk, air pollution

Study finds that children with high exposures to air pollution, and lower exposure to green spaces have an increased risk of developing ADHD

Taking data from 37,000 children from Vancouver, researchers find that higher air pollution – due to PM2.5 particles and very low levels of green space – can increase childhood ADHD risk by up 62%.

In contrast, children living in greener and less polluted areas have a 50% lower risk of developing the mental disorder.

Estimating the possible effects of air pollution exposures in relation to ADHD, and the possible associations between exposure to greenness, and noise in early life, researchers calculate incidence of ADHD with these variables.

ADHD is one of the most prevalent neurodevelopmental disorders. Affecting up to 5-10% of children, it can be bought on by exposure to environmental toxins like lead, maternal drug use, alcohol use or smoking during pregnancy – and now, air pollution.

Positive environment exposures – like green spaces – can benefit mental health

Published in Environment International, the researchers took administrative data of births in Metro Vancouver, Canada, between 2000 to 2001 – salvaging data on ADHD cases from hospital records, physician visits and prescriptions, looking at severity and environmental exposures.

To calculate the amount of green space in neighbourhoods where the participants were from, researchers estimated with a satellite metric, while the residential levels of two air pollutants: NO2 and PM2.5, as well as noise levels were estimated using available exposure models.

From this, they found around 1,217 cases of ADHD, which is equivalent to 4.2% of the total study population.

When analysing green spaces, the research exposed that participants who were living in areas with a higher percentage of vegetation had a lower risk of ADHD – displaying that a 12% increase in vegetation percentage was associated with a 10% reduction in ADHD risk.

Conversely, when estimating effects of air pollution, an opposite association was noted with PM2.5where participants with a higher exposure to fine particles had higher ADHD risk (every 2.1 µg increase in the levels of PM2.5 translated into an 11% increase in the risk of ADHD).

However, no relations were found for the rest of environmental exposures assessed: NO2 and noise.

Noise and nitrogen had minimal effect on ADHD development

Associations between green space and air pollution with ADHD were reflective of former studies on ADHD. However, most of the other research had focused on the evaluation of single exposures and rarely calculated joint effects of multiple environmental exposures, such as green spaces and noise.

Lead author Matilda van den Bosch said: “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.”

Weiran Yuchi, researcher at the University of British Columbia, and first author of the study, added: “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 neutralized each other.”


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