In a time-stratified, case-crossover study, exposure to both large and small particulate matter, as well as to nitrogen dioxide, was significantly associated with increased odds of death from myocardial infarction (MI).
Investigators found “consistent evidence” that short-term exposure to particulate matter with an aerodynamic diameter of 2.5 μm or smaller (PM2.5), particulate matter with an aerodynamic diameter less than 10 μm (PM10), and nitrogen dioxide (NO2) was associated with increased risk for mortality from MI, they write.
The study was published in the January 26 issue of the Journal of the American College of Cardiology.
“These findings add to the understanding of acute adverse effects of air pollution on cardiovascular mortality and highlight the needs for either general population or policy practitioners to take effective measures in reducing air pollution exposures, especially for older adults and those with higher risk of MI occurrence,” write Yuewei Liu, MD, PhD, Sun Yat-sen University, Guangzhou, China, and colleagues.
Short-term exposure to ambient air pollution has previously been linked to MI occurrence, but only a limited number of studies have investigated its association with death from MI, and the results remain inconsistent, the researchers write.
To explore this end point further, the researchers looked at 151,608 deaths from MI that occurred in Hubei Province from 2013 to 2018.
They assessed exposure to PM2.5, PM10, sulfur dioxide (SO2), NO2, carbon monoxide, and ozone on the day before the MI (control day) and the day of the MI (case day).
Assessments of air pollutant exposure were based on the address of each patient who died from MI death, and were weighted according to how close the patient lived to the air pollution monitor.
Of the MI deaths that occurred from 2013 to 2018, 98.2% were from acute MI, 54.0% were male, 41.0% were younger than 75 years of age, and 55.8% died in the winter.
Overall, the mean daily exposure to PM2.5 was 63.4 μg/m3.
The study showed that exposure to PM2.5, PM10, and NO2 (mean exposure on the same day of death and on the previous day) was significantly associated with increased odds of MI mortality. This increased as exposure increased, until the pollution level reached a breakpoint of 33.3 μg/m3.
Each 10 μg/m3 increase in exposure to PM2.5 (<33.3 μg/m3), PM10 (<57.3 μg/m3), and NO2 was significantly associated with a 4.14% (95% CI, 1.25% – 7.12%), 2.67% (95% CI, 0.80% – 4.57%), and 1.46% (95% CI, 0.76% – 2.17%) increase in odds of MI mortality, respectively.
The association between NO2 exposure and MI mortality was significantly stronger in older adults (75 years and older) than in younger adults (70 years and younger).
No consistent association between sulphur dioxide, carbon monoxide, or ozone and MI was seen in this study, the researchers note.
Air Pollution Revolution
The results from this study “from Hubei Province (capital city Wuhan), a region with the twin notoriety of originating COVID-19 but also perennially exposed to high levels of air pollution, provides a clear relationship” between high levels of air pollution and CV mortality, write Sanjay Rajagopalan, MD; Herman K. Hellerstein, MD, professor of cardiovascular research, Department of Internal Medicine and Radiology, Case Western Reserve University, Cleveland; and Jagat Narula, MD, associate dean for global affairs and Philip J. and Harriet L. Goodhart Professor of Medicine, Mount Sinai Hospital, New York City, in an accompanying editorial.
The strengths of this study include the relatively large number of cardiovascular deaths, multipollutant sensitivity analyses, and its case-crossover design, the authors note.
“This design offers the advantage of controlling for confounding from fixed or slowly varying individual-level characteristics through time-stratified referent selection (i.e., the day before or after the event).”
China is well placed to do such air pollution studies, Rajagopalan told theheart.org | Medscape Cardiology. About 8 years ago, the country faced a severe crisis, where air pollution from burning coal caused a huge number of deaths.
“In China, there has been a revolution, since 2011/12, when they had such bad air pollution epidemics that they went into ‘warp speed’ in terms of cleaning up air pollution. They installed monitors to measure air pollutant concentrations in cities. This has been happening over the last 8 years, and now it’s even more dramatic. In this particular study, they placed 109 monitoring stations within a 100 kilometer barrier, which is roughly one monitor over a 1 square kilometer area, which is pretty good,” he said.
It turns out people die of air pollution, not because of lung disease or other respiratory illness, but because of heart attacks.
“It turns out people die of air pollution, not because of lung disease or other respiratory illness, but because of heart attacks. More than 58% of lives lost every year because of air pollution, and every year, there are probably more than 9 million deaths attributable to air pollution globally. So if you combine air pollution, both indoor and outdoor, it’s probably one of the top four causes of global mortality, so it has a very big impact worldwide because everybody’s exposed; nobody is spared,” Rajagopalan said.
The results of this study also highlight the “important influence” of vehicular emissions in the form of NO2 play in cardiovascular mortality, he said.
“These gases are important because they are emitted principally by traffic emissions. Sulphur dioxide is an indication of coal. I live in Ohio and I see a lot of illness from the coal mining going on in West Virginia. It’s silly to be doing coal mining and burning coal in 2021. Hopefully, that practice is going out and there’s clean energy coming,” he said.
If there is one bright note to take from the pandemic, it’s that NO2 and other air pollutant emissions have dropped. Less air travel, less traffic, fewer people commuting to work have all contributed to lessen emissions.
“One silver lining in the dark cloud of COVID-19 has been the singular impact of the pandemic on global air pollution emissions. Early in the pandemic, when there was a complete shut down of road traffic and air travel in many parts of the world, there was a dramatic impact on air pollution levels,” Rajagopalan said. “PM2.5 plummeted across the globe, resulting in ‘blue sky days,’ allowing anyone to ponder a future free from air pollution.”
People are starting to become more conscious of air pollution and ways to prevent it, he said.
“What is nice is a lot of people are beginning to understand our relationship between Earth and the environment,” he added. “We have to do all we can. We are at a critical stage in our planet’s trajectory with global warming, so anything you can do to reduce your own footprint, every small step, helps.”
The study was supported by the Hubei Provincial Health Commission in China, the Fundamental Research Funds for the Central Universities, the National Natural Science Foundation of China, and the Jiangsu Social Development Project. Rajagopalan and Narula have reported that they have no relationships relevant to their comments.