Kids who grow up around more green space have lower risk of ADHD, study suggests

A study by researchers from the University of British Columbia suggests that children who grow up around more green space are less likely to develop attention deficit hyperactivity disorder (ADHD).

ADHD occurs in five to nine per cent of children worldwide, according to the Centre for ADHD Awareness (CADDAC).

It is a chronic condition and can lead to an inability to properly regulate attention and emotions, and is the most common neurodevelopmental disorder among children.

However, it is still unknown what exactly causes the condition. The two main causes are thought to be genetics and environmental risk factors such as air pollution.

"We know [air pollution] can create a lot of inflammation in the body that could actually affect features of the brain," said Dr. Michael Brauer from the UBC School of Population and Public Health and one of the authors of the recent paper, published in the journal Environment International.

"So we thought, here's a condition [ADHD] … that has certainly been linked to brain development. If air pollution also affects brain development, is there a link here?"

The paper looked at more than 37,000 children born in Metro Vancouver in the year 2000, and tracked their developmental progress through hospital records and physician visits until they were 10 years old.

This data was then analyzed through various metrics: the green space surrounding their home postal codes, exposure to fine particulate matter and nitrogen dioxide, as well as noise.

Subsequently, scientists discovered that children who grew up around more green space, and were exposed to less particulate matter, had a lower likelihood of developing ADHD.

"If you compared [children who grew up around] the least air pollution and the highest amount of vegetation, to the [ones who grew up around] most air pollution and lowest amount of vegetation … there was about a twofold difference in the risk of developing ADHD," Brauer said.

Advocate asks for more research

Heidi Bernhardt, director of education and advocacy at CADDAC, said the study was "interesting," but would likely not be groundbreaking in the field of ADHD research.

Bernhardt says the fact the study did not analyze whether parents had ADHD themselves was concerning, given how heritable ADHD is.

She says another limitation with the study was a lack of controlling for individual socioeconomic factors among parents.

The study attempted to control for the socioeconomic status of the children as they grew up, although it notes that the analysis was based on the average income in the neighbourhood where the children lived — not on their individual families' wealth.

"We have to be very careful that we don't report these things [association with green space] as a cause," she said.

"We have to do far more studies before there's any conclusions drawn — studies that actually take out all of these other things that could be factors."

Green space mediates effect of pollution

The paper found that green space — parks, natural canopy, and trees — helped reduce the effects of air pollution, even if there were high amounts of particulate matter in a given neighbourhood.

"This sort of access to nature, exposure, and vegetation could be really important," Brauer said. 

"We are sort of evolutionarily programmed to be living in a natural setting, so the urban areas that we live in now are not really what we're designed to live in."

Brauer says that even the act of crossing the street can be more stressful than the relatively calming effect of being in nature.

Bernhardt says it would "stand to reason" that children with ADHD would be calmer and less stressed in nature than if they were in a classroom environment, and that green space could indeed be a mitigating factor for their symptoms.

Brauer says the research could have important implications for city planning going forward, as part of a body of research showing the positive effects of green space on children.

"We're not planting trees, you know, thinking that we may reduce the likelihood of ADHD," Brauer said. "But we may actually see these benefits.

"We can actually correct some other problems using climate change and the need to respond to that as a kind of driver."