City parks and green spaces help counter the heat, boost biodiversity, and instill a sense of calm in the urban jungle.

They also help slow biological aging, with people who have access to green spaces found to be on average 2.5 years biologically younger than those who do not, according to a new study published Wednesday in Science Advances.

"Living near more greenness can help you be younger than your actual age," Kyeezu Kim, the study's lead author and a postdoctoral scholar at Northwestern University's Feinberg School of Medicine, told AFP.

"We believe our findings have significant implications for urban planning in terms of expanding green infrastructure to promote public health and reduce health disparities."

Exposure to green spaces has previously been linked with better cardiovascular health and lower rates of mortality.

It's thought that more physical activity and social interactions are at play, but whether parks actually slowed down aging on a cellular level has been unclear.

To investigate, the team behind the study examined DNA chemical modifications known as "methylation."

Prior work has shown that so-called "epigenetic clocks" based on DNA methylation can be a good predictor of health conditions such as cardiovascular disease, cancer, cognitive function, and a more accurate way of measuring age than calendar years.

Kim and colleagues followed more than 900 white and Black people from four American cities — Birmingham, Chicago, Minneapolis, and Oakland — over a period of 20 years, from 1986-2006.

Using satellite imaging, the team assessed how close the participants' residential addresses were to surrounding vegetation and parks, and paired this data with blood samples taken in years 15 and years 20 of the study, to determine their biological age.

The team constructed statistical models to evaluate the results, and control for other variables, such as education, income, and behavioral factors like smoking, that might have affected the results.