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Cherry blossoms in Toronto's High Park could increase your life expectancy. (Kimberly Gale/CBC)

Most people expect that getting married or a promotion will make them happier. But how many realize that living near a park can do the same thing?

A recent study of major U.K. cities showed that when communities are surrounded by more green space, life expectancy increases significantly.

The world is currently on track for an estimated 1.3 billion people to become city dwellers between now and 2030, said Alan Logan, co-author of Your Brain on Nature.

With denser cities increasing pressure on green space, negative consequences for human health may be the result. Access to green space is clearly a public health issue, said Logan.

Logan will be speaking about his work at the The Organic Vision conference in Toronto on Saturday, Feb. 22.

Nature exposure influences the natural killer cells that defend us against the common cold, influenza and cancer, he said.

In a Japanese study, a group spending three days in a forest setting produced significantly more natural killer cells in their bodies than a group that spent three days sightseeing in the city, said Logan. The positive results persisted for at least a month.

It’s not known exactly what causes this effect but phytoncides may be partly responsible. These are chemicals secreted into the air from trees, especially evergreens. They have been shown in the lab to stimulate the production of killer cells. They hover in greatest concentrations in natural settings, such as forests, about four feet off the ground.

Nature’s positive effect on mental health is another important recent discovery.

"Access to green space is clearly a public health issue," says researcher Alan Logan.

Mental health and well-being is a critical modern public health issue, according to the World Health Organization, and depression is now the leading cause of disability in middle to high income countries. Increasing urbanization may be partly to blame because they tend to detach people from the natural environments they evolved in.

People moving to towns with more parks and gardens not only report greater well being than those without access to those amenities, but their improved mental health lasts for at least three years after their move, according to results of a study published in the journal Environmental Science and Technology by Ian Alcock of the University of Exeter Medical School.

These findings raise the possibility of improving public health through urban design, said Alcock. Providing more urban green space could help better public health at relatively little cost and in a drug-free way, he said. 

But to harness the benefits of nature, designers must to go beyond providing low-maintenance landscapes as are often found in privately-owned public spaces popping up around new condominium developments. "Just putting in pavement and benches doesn’t add anything that has restorative qualities for people," said Elizabeth Nisbet of the psychology department of Trent University.

A rolling topography, rather than a flat landscape, can make for a successful urban park, said Julia Africa of the Centre for Health and the Global Environment at the Harvard School of Public Health. Paths that wind, allowing the viewer to be drawn into the landscape, to be intrigued by the structure of trees, or small niches where there are certain types of blooming flowers, are some other features of the best urban parks.

Manicured, astroturfed landscapes do not produce the same health benefits, said Nisbet. Triggering fascination and curiosity in the world around us is critical. “When there’s no diversity, there’s no interest.”

When you have something to look at that’s natural, a few trees or shrubs, it actually restores your attention, by allowing your brain to actually pause and rest, she said.

But while nature’s health effects have been documented, what we don’t know is the dose, said Africa. “Is it one tree or a whole forest?”

All the research points to more nature needed in more cities. Just how to incorporate it into already-established urban areas is the challenge.

One strategy is to take nature higher, said Africa, citing the successful High Line elevated park in New York City. Another is to simply add nature wherever possible. Street trees are an example.

Where urban planners fail to bring sufficient nature to the city, there’s no stopping urbanites from travelling to whatever park is closest at hand, said Alcock.

Alan Logan will be speaking about his work at the The Organic Vision conference in Toronto on Saturday February 22.