I like greenery. I like the idea of cities that are covered in plant life, for a whole host of reasons, many of which I’ve gone into before. It’s fair to say that I’m already pretty convinced that this is a good idea, but now another piece of evidence has come along:

Published in the journal JAMA Network Open, the study found that exposure to greenspace around one’s home and surrounding neighborhood could improve processing speed and attention, as well as boost overall cognitive function. The results also showed that lowered depression may help explain the association between greenspace and cognition, bolstering previous research that has linked exposure to parks, community gardens, and other greenery with improved mental health.

“Some of the primary ways that nature may improve health is by helping people recover from psychological stress and by encouraging people to be outside socializing with friends, both of which boost mental health,” says study lead author Marcia Pescador Jimenez, an assistant professor of epidemiology. “This study is among the few to provide evidence that greenspace may benefit cognitive function in older ages. Our findings suggest that greenspace should be investigated as a potential population-level approach to improve cognitive function.”

For the study, Pescador Jimenez and colleagues from SPH, Harvard T.H. Chan School of Public Health, Brigham and Women’s Hospital, Harvard Medical School, and Rush Medical College estimated residential greenspace with a satellite image-based metric called the Normalized Difference Vegetation Index (NDVI). They measured psychomotor speed, attention, learning, and working memory among 13,594 women aged 61 on average and primarily White, from 2014 to 2016. The women were participants in the Nurses’ Health Study II, the second of three studies that are among the largest investigations into the risk factors for chronic diseases among US women.

Adjusting for age, race, and individual and neighborhood socioeconomic status, the researchers found that greenspace exposure was associated with psychomotor speed and attention, but not learning or working memory.

In addition to depression, the researchers also examined the potential roles of air pollution and physical activity in explaining the association between greenspace and cognitive function, and they were surprised to only find evidence of depression as a mediating factor.

“We theorize that depression might be an important mechanism through which green space may slow down cognitive decline, particularly among women, but our research is ongoing to better understand these mechanisms,” Pescador Jimenez says. “Based on these results, clinicians and public health authorities should consider green space exposure as a potential factor to reduce depression, and thus, boost cognition. Policymakers and urban planners should focus on adding more green space in everyday life to improve cognitive function.”

While the study shows evidence of this association, the greenspace metric that the researchers used to measure greenspace exposure does not differentiate between specific types of vegetation. In a new project funded by The National Institute on Aging, Pescador Jimenez will apply deep learning algorithms to Google Street View images to better understand which specific elements of greenery, such as trees or grass, could be the driving factors for health.

The researchers also hope that their study is replicated among other racial/ethnic populations and assesses associations with cognitive decline over longer periods of time.

“The distribution of green spaces in cities is not uniform,” says Pescador Jimenez. “Increasing everyday access to vegetation across vulnerable groups in urban cities is a crucial next step to achieve health equity.”

That last point is key. Not only is distribution of green spaces not uniform, but there’s also almost always a strong racial element in determining the healthiness of one’s surroundings. If you want more on that, Mano Singham did a good writeup to go with John Oliver’s video on environmental racism in the United States. Unfortunately the racial and economic microcosms we often see in my home country are often replicated at a global scale. This is part of why I focus so much on politics – if we can’t change how humanity is run, then even if we manage to survive climate change, we’re going to keep running ourselves into crisis after needless crisis. Among other things, I think that means improving the quality of life of those at the bottom, and uplifting the rest of us as they catch up, and resources allow. Improving where people live should be a big part of that.