Based on the observation that urbanization and increased rates of depression and anxiety disorders were happening simultaneously, researchers in Holland began studying the connection. So did Dr. Mathew White, an environmental psychologist at the University of Exeter.
"In particularly built up urban areas, with very little green space and parks, anxiety and depression rates were higher, even after controlling for things like area level, socioeconomic status and people’s income and that kind of stuff," he explained.
So White and his team followed the data of 12,000 people over 18 years, looking at families representative of the U.K. population.
"We looked at how their own levels of anxiety and depression changed as they moved to more built-up areas or areas with more green space," he said.
"What you find is the years when they’re living in greener areas, they’re showing less signs of depression and greater subjective well-being. Their life satisfaction is higher."
They also discovered that when people moved into areas with more green space, improvements in mental health happened immediately. Those effects also lasted for years as levels of reported well-being remained high.
"People don’t adapt to the more green space," White said. "We thought that people would get used to it but they don’t, which is quite encouraging for policy makers to defend the development of parks."
White was recently in front of the U.K. parliament discussing the outcomes of this study, as the value of green space is being weighed against pressure from developers.
But how much green space is needed to see a measurable, positive effect?
"We’re not entirely sure," White admitted. "We expect there’s some diminishing marginal return. So when you look at rural communities, which are very much green space, we don’t find the same relationship. We are finding it in urban areas, so it seems there is a threshold but we don’t know what it is yet."
The U.K. has a more temperate climate than Canada, with more greenery year-round. But a similar study in Wisconsin replicated White's findings. Studies in Sweden based on 21 years of data have shown antidepressant use goes up during summers with poor weather.
There is certainly more to be studied to get to the bottom of why and how green space is so beneficial to mental health. White and his team are taking what they learned and applying it to other environments, to see if both real and virtual green space in medical facilities can improve patient mood.