The study included data on the prevalence of 24 different health conditions treated over the course of a year among about 350,000 patients seen at 96 practices.
For 15 of the 24 conditions, the annual prevalence was lower among patients living in the greenest areas, even after the researchers controlled for factors known to influence health.
Among the other major findings:
The impact was greatest for mental health conditions. Compared to people living in areas with the least green spaces, those living in areas with the most were a third less likely to have anxiety disorders that required treatment and roughly one-fifth less likely to receive treatment for depression.
Among the physical health conditions, the apparent protective benefits of living in greener areas appeared strongest for respiratory diseases such as asthma, COPD, and upper respiratory infections.
A much weaker association was seen for other common health conditions, including cardiovascular disease, diabetes, and cancer.
Surprisingly, greater access to green spaces appeared to have no impact on health of people living in the most urban neighborhoods included in the study.
The researchers speculate that this might be because green spaces in poor, highly urban areas may not be used as much because they are perceived as unsafe.