Urban Heat and Air Pollution May Harm Developing Brains in the Womb, Study Suggests

During a typical summer day in New York City, residents and visitors alike face an onslaught of blistering heat and air pollution, each responsible for a host of health problems—from heat stroke to lung cancer. 

Now, in a first-of-its-kind longitudinal study, researchers at Queens College, Mount Sinai Hospital and the City University of New York’s Graduate Center say that list should include harms to the brains of unborn children.

The researchers tracked the progression of 256 New York City children from the womb through adolescence. The findings suggested that pregnant women exposed to a combination of high temperatures and polluted air during their second and third trimesters experienced a drop in progesterone, one of pregnancy’s vital hormones. 

“There’s a suite of hormones interacting between the pregnant person and fetus. Heat and air pollution may influence these, at least in part, through inflammatory pathways, affecting fetal brain development and programming for later life,” says Perry Sheffield, associate professor of pediatrics at Icahn School of Medicine at Mount Sinai and a co-author of the study. 

While women naturally experience some fluctuations in progesterone, the researchers found that prolonged heat and air pollution can cause progesterone to hit abnormally low levels. When that happens at key points of pregnancy, the study suggests, it contributes to later behavioral challenges in the exposed children, such as anxiety, depression, social withdrawal, impulsivity, aggression and hyperactivity.

Pregnant women living in some of New York City’s poorest areas are a part of the most vulnerable group, the study found, with their children facing greater risks as a result of prolonged heat and air pollution exposure. 

Scientists believe that these risks are compounded by what climate scientists refer to as the “urban heat island effect.” Fewer trees and green spaces make cities warmer than outlying areas, and the least-green parts of cities tend to be the hottest of all. 

Many lower-income housing facilities in New York City are old, lacking proper air conditioning and ventilation. Higher electricity costs are another challenge: Rates in the New York metro area were more than 50 percent above the national average as of the end of last year, according to federal figures. 

Yoko Nomura, the study’s principal investigator, says that for too many people, these inequalities make it impossible to dodge the sweltering heat and suffocating air even indoors. 

“This urban heat island effect makes exposure to high temperatures and pollution worse, especially in areas without greenery. Policymakers need to understand that,” Nomura said in an interview. 

To combat both heat and air pollution, the city of New York operates cooling centers, enforces regulatory air policy and helps lower-income residents purchase air conditioning units. However, a 2022 report from the city comptroller found that cooling efforts weren’t distributed equitably throughout New York City. Among the comptroller’s recommendations: Create more green spaces in heat-stressed areas. 

“The challenge is aligning urban design with environmental performance, and doing it equitably,” said James Voogt, professor of geography at Western University in Ontario, who was not involved in the longitudinal study. “For example, planting more trees might be a solution. But if the property values go up and people are forced out, it doesn’t necessarily solve the problem.”

City residents working on these issues say they’re fed up. 

“Harlem residents have been disproportionately impacted by climate change due to extreme heat. It’s rooted in environmental racism and practices like redlining,” said Caleb Smith, resiliency coordinator at the Harlem-based group WE ACT for Environmental Justice. “It doesn’t even take what the National Weather Service calls an ‘extreme heat emergency’ for heat to start having serious impacts on health.”

Last summer, 21 city council members sponsored a bill that would require building owners to install cooling systems in tenant-occupied buildings. A committee hearing in late 2024 was the last action taken on it. 

Smith, who has struggled to afford running their air conditioning, said that the city must elect a mayor who will address the impacts of climate change on New York City.

“The next mayor must recognize that climate change doesn’t exist in a vacuum,” Smith said. “It’s directly tied to cost-of-living issues and equity.”

Nomura agrees, saying that her team’s research serves as a call to action for the health care system to adopt public health strategies that are more inclusive and responsive. 

“Climate change isn’t fully recognized in healthcare yet. Vulnerable populations can’t escape the heat, unlike people with resources who can leave,” she said. “Our goal is to provide systematic data so public resources can reach those who truly need help.”