Over the course of 3 years, pregnant women living in Vancouver’s greenest neighborhoods delivered healthier babies than those in less tree-lined communities.
Why are certain neighborhoods healthier than others?
It's a question that's received no small share of academic attention in recent years (CityLab has variously touched upon the topic here, here, and here.) With no definitive single answer, the discussion continues to expand. Is it accessibility to nutrition—living near and being able to afford Whole Foods versus 7-Eleven? Perhaps it's economic segregation, which can starve low-income minority populations "of access to key social goods, such as education, health care, adequate housing, [and] recreational amenities," according to one relevant study by the University of California, San Francisco's Center for Health and Community.
Now we can add the relative presence of trees, leaves, grass, and other greenery to the healthy neighborhood equation. Greener neighborhoods, according to a study recently published in Environmental Health Perspectives, are associated with healthier births for new mothers.
Over the course of three years, the researchers found, pregnant women living in Vancouver’s greenest neighborhoods (see the map below) delivered far healthier babies than those living in less tree-lined communities. These women were more likely to have full pregnancy terms, and their newborns were 12 grams heavier on average than babies born to women residing in areas with limited vegetation. Additionally, pregnant mothers from the leafiest neighborhoods had the fewest recorded “very pre-term births” (a pregnancy lasting less than 30 weeks).
“From a medical standpoint, those are small changes in birth weight,” says Perry Hystad of Oregon State University, the study’s lead author. “[B]ut across a large population, those are substantial differences that would have a significant impact on the health of infants in a community.” In all, the health records of over 64,000 newborn children were examined.
Defining the “greenest neighborhoods” in a given city is a tricky task. San Francisco and Portland, Oregon, for instance, are densely populated, but residents have significant access to parks and outdoor recreation areas. This study used technology to determine the level of greenness in each Vancouver postal code: The city’s topography was rendered by cloud-free images taken via satellite. Each neighborhood’s level of vegetation was then adjusted for seasonal and annual fluctuations. Lastly, Vancouver’s residential areas were adjusted for walkability, as well as for their noise and air pollution levels.
“We determined that increased residential greenness is associated with positive birth outcomes in a population,” the seven-person research team concluded. Interestingly, these health benefits remained even when controlled variables like air pollution and distance from the nearest park were altered. The authors weren't able to pinpoint what precisely makes vegetated neighborhoods healthier environments for pregnant mothers, but “psychosocial and psychological influences,” could be at play, they say.
In past research, greener areas have also been associated with lower blood pressure. Neighborhoods filled with greenery appear to act as stress reducers.
In Vancouver, being born into one of the city's greenest neighborhoods appears to be a luxury of those with relatively high incomes, meaning lower-income residents are often excluded from their benefits.
As the figure above demonstrates, Vancouver’s greenest neighborhoods are largely occupied by the city’s wealthiest residents. A mere 8.3 percent of pregnant women under study who were among Vancouver’s highest earning class lived in the city’s least green areas; more than half of them lived in Vancouver’s two greenest neighborhoods. Pregnant women from the lowest income level, meanwhile, were four times as likely to live in the least green areas, where higher ratios of premature births were recorded.
So does this study just show that wealthier mothers, whom we already know tend to give birth to healthier infants, also tend to live in greener neighborhoods? Hystad says no: even when he and his co-authors controlled for income, the relationship between healthy births and greener neighborhoods was still there. Which means, he argues, that the inaccessibility of green areas by low-income residents raises important public policy questions.
"What you find in this study is that the greenest areas were the most affluent areas," Hystad says. "This could definitely play an important role in trying to address the income injustices that play into our neighborhoods."
How could such disparities be addressed? Prioritizing green space in areas populated by low-income residents may be one way—an unconventional tool urban planners could consider deploying in response to neighborhood-by-neighborhood inequities. As Thomas Laveist, director of the Johns Hopkins Center for Health Disparities Solutions, told CityLab back in 2011.
“Solutions to health disparities are likely to be found in broader societal policy and policy that is not necessarily what we would think of as health policy. It’s housing policy, zoning policy, it’s policy that shapes the characteristics of communities.”
The debate about how to build healthier neighborhoods will go on, but we can and should add making neighborhoods greener to the list of possible approaches.