Air Pollution, Whether Outdoor or Indoor, Ups Death Risk

Breathing in pollution, whether outdoors in the open air or indoors thanks to fuel use in a poorly ventilated home, increases the risks of all-cause and cardiovascular death over a 10-year period, according to an observational study of more than 50,000 adults living in Iran.

Findings from the Spatial Assessment of Cardiovascular Events (SPACE) study, published online recently in PLOS ONE, “demonstrate that the burden of disease attributable to the environment may be as large as traditional cardiovascular risk factors,” the researchers say. The issue, they add, “thus represents a critical opportunity for targeted policies and programs.”

What inspired SPACE, said senior author Rajesh Vedanthan, MD, MPH (NYU Langone Health, New York, NY), is the ever-growing body of literature that shows environmental factors—not only air pollution but also things like traffic noise, population density, exposure to artificial light at night, proximity to healthcare facilities, and access to green space—can impact cardiovascular health.

However, he told TCTMD, most prior studies “have looked at these factors in isolation, not in a combined format, and many of the studies have been done in high-income countries.” Here they sought to better understand how spatial environmental factors—capturing the essence of a geographic place—impact people with a low income living in a middle-income country.

Worldwide, the paper notes, environmental factors led to around 11 million deaths in 2019. Five million of those were due to cardiovascular disease. As reported by TCTMD, the climate crisis is set to upend cardiology by worsening the environment in countless ways.

Vedanthan said the model they used to do their calculations allowed them to tease out how much the various factors independently contribute to the overall risk.

For instance, when earlier analyses looked at nighttime light pollution on its own, they found an increase in cardiovascular mortality with exposure to brighter nights. But “when you put it in the combined model, it actually did not end up being significant,” he explained. “That’s probably because folks who are in situations with high nighttime light, let’s say in big cities, are also probably exposed to traffic, air pollution, and other things. Once you take those other factors into account, the independent effect of nighttime light is less strong.”

SPACE Study

Led by Michael B. Hadley, MD, MScPH (Icahn School of Medicine at Mount Sinai, New York, NY), Vedanthan and colleagues analyzed data from a cohort of 50,045 people (58% women) living in Iran’s Golestan province. All were enrolled in the Golestan Cohort Study from 2004 to 2008, and they ranged in age from 40 to 75 years. Around 80% resided in rural villages, while the rest lived in a city with approximately 130,000 residents. Most were married (88%) and illiterate (70%). Just 7% had diabetes, 6% had a history of ischemic heart disease or stroke, and 20% had hypertension. Around one in five used tobacco (22%) and opium (17%), while 3% reported drinking alcohol.

Over a 10-year follow-up period, 5,996 of the study participants died, with 2,733 of those deaths being cardiovascular.

The researchers considered eight environmental risk factors: ambient fine particulate matter (PM_2.5) air pollution (which averaged 33.5 μg/m³ each year), household fuel use and ventilation (71% used kerosene, 12% used gas, 9% used mixed fuels, and 7% used biomass like wood or dung), proximity to traffic (34% lived close to major highways), distance to PCI center (which averaged 92.2 km), neighborhood socioeconomic status, population density (which averaged 1,732 people per km²), local land use (57% of households were amid cropland and 25% were in urban settings), and nighttime light exposure.

They adjusted for sex, age, person-level socioeconomic status, obesity, diabetes, hypertension, physical inactivity, CVD history, and substance abuse. After adjustment, several of the environmental risk factors were independently associated with both all-cause and cardiovascular death, though not all of the associations reached statistical significance.

Independent Risk Factors Linked to Mortality: Adjusted HR (95% CI)

Proximity to traffic was linked to all-cause death (HR 1.13; 95% CI 1.01-1.27) but not cardiovascular death. Neighborhood socioeconomic status, local population density, nighttime light, and land use were not associated with mortality.

Other factors that independently predicted higher risk of both all-cause and cardiovascular mortality were older age, male gender, being unmarried, having lower socioeconomic status, illiteracy, higher waist and lower hip circumference, physical inactivity, tobacco and opium use, and histories of hypertension, diabetes, ischemic heart disease, and stroke.

Vedanthan said that although certain environmental risk factors, like the use of biomass fuel, may be more prominent in particular regions like Iran, there are parallel examples elsewhere. In New York, gas-burning stoves are a common source of unsafe air, he noted. Late last year the city banned the installation of gas in new buildings being constructed.

“Thinking about these spatial environmental factors, whether they be outdoor or indoor air pollution, whether they be the broader socioeconomic environment, that definitely has relevance around the world,” he commented.

And while there are things that individual people can do, much needs to be tackled “collectively as a society,” Vedanthan said. Policy makers should “put into place the kinds of codes, regulations, standards, etc, that will keep our environments as healthy as possible.”

Hadley, in a press release, offered suggestions on how their findings, culled from publicly available data, might be applied: in the creation of “risk maps” for communities. “Eventually, we expect health systems to use similar approaches to create environmental risk maps for the communities they serve,” he says, adding, “The data can empower physicians to estimate environmental risks posed to their patients and offer individualized recommendations to mitigate risk.”