Children and poor people suffered disproportionately from lack of green acres, the researchers found.
The study findings were published online Thursday in the Journal of Epidemiology and Community Health.
Any number of factors could account for the benefits of green space, experts said.
More natural sunlight, for instance, has been linked with a lower incidence of Seasonal Affective Disorder (SAD) and other benefits.
"If patients in hospitals have direct exposure to sunlight through a window or natural sunlight, hospital stays are shorter and patients have less complications," Rakel said. "That's been well-established.
More light also means more vitamin D in the skin, which has been found to elevate mood and improve muscle strength, he added.
And fresh air, obviously, has a benefit as well, as do the exercise opportunities that come with more open space.
But much of the relief may come from the simple ability to de-stress.
"If we're in a busy street with more technology and artificial things, we're going to be multi-tasking more, which prevents us from focusing on one thing," Rakel said. "In this day and age, we really need some sort of centering practice. We need to get our mind out of its own stories and focus on something that's pure. Nature is a beautiful example of that -- it's the way things were meant to be."
This study has "implications not only for city planning but also for indoor design and architecture," said Richard Ryan, professor of psychology, psychiatry and education at the University of Rochester Medical Center. But the benefit is proportional to how much people pay attention to nature, he said.
"If they're in th
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