New research suggests that city-dwellers who live on tree-lined streets are healthier than those who don't see much nature in their day-to-day lives.

In fact, the study went so far as to quantify the benefit of greenery, and found that having 10 more trees on a city block makes people feel as healthy as getting a US$10,200 raise, or being seven years younger. 

This isn't the first study to find a link between nature and wellbeing. Research earlier this year showed that being in nature for just 90 minutes could change a person's neural activity in a way that helps their emotional regulation.

"When compared to rural folk, people living in cities have a 40 percent higher risk of mood disorders and a 20 percent higher risk of anxiety disorders. They're also twice as likely to develop schizophrenia," Peter Dockrill reported for us at the time.

Research has also shown that climbing a tree can help to improve cognitive ability, and getting away from electricity for just one week can reset your body clock.

But the new study from researchers at the University of Chicago in the US takes things a step further. "We have known that the natural environment can improve health, but this study shows for the first time how big that impact can be," said lead researcher Marc Berman in a press release. 

To do this, the researchers took data from the Ontario Health Study, which regularly surveys more than 30,000 people in Toronto, Canada, on their health. They also measured green space around the city using high-resolution satellite images, and existing data on 530,000 trees. 

When they compared the two datasets, and controlled for factors such as income and age, they found that 10 extra public trees on a block made people feel 1 percent healthier - the same increase as earning US$10,200 per year more, moving to a neighbourhood that's US$10,000 wealthier, or being seven years younger.

The researchers didn't just look at self-measured health either, when they reviewed data on cardio-metabolic conditions such as obesity and heart disease, they found that the health benefits of 11 extra trees were equivalent to earning US$20,200 extra a year.

"Although people in more affluent neighbourhoods had better health, people in less advantaged neighbourhoods with plentiful trees reported health that more closely matched the affluent residents," the release explains. "Likewise, affluent people who lived in neighbourhoods without a generous tree canopy, such as new housing developments, had health reports more like those of people in poorer communities."

Of course, Berman is quick to point out that their research has only found a correlation between trees and better wellbeing, and there's no mechanism we know of that makes greenery improve our health. But the size of the study still makes the results pretty interesting. 

"A number of things could account for the difference. Maybe people in communities with trees walk more. The results could also be driven by better air quality," Berman said. Reduced stress could also play a role.

Although we don't have a definitive answer just yet, hopefully studies like this one remind city planners that green space is an important part of the metropolises of the future. And if nothing else, planting more trees is always going to be good for the planet.

The research has been published in Scientific Reports.