A recent international study published in The Lancet Planetary Health showed that long-term exposure to fine particulate outdoor air pollution is a key contributor to cardiovascular disease and death throughout the world, regardless of the income bracket of the various countries.1

Furthermore, the study showed that even small reductions in the level of air pollution could result in reduced mortality. Previously, most air pollution studies looked at the impact on the health of people in high-income countries, where generally lower concentrations of air pollution have been documented.1

The study was also able to demonstrate that it is not necessary to completely eradicate all outdoor air pollution in order to see improved effects on people’s health, said study lead author Perry Hystad, an environmental epidemiologist in Oregon State University's College of Public Health and Human Sciences, in a press release.2

"If you reduce the concentration of outdoor air pollution, you're going to see benefits for cardiovascular disease," Hystad said in a press release. "Before this study, we were not sure if this was the case. Some studies suggested that at high concentration, as seen in many developing countries, levels would have to be reduced by very large amounts before health benefits would occur."2

Using data gathered from the Prospective Urban Rural Epidemiology (PURE) study, the researchers analyzed 157,436 adults between the ages of 35 and 70 years in 21 countries from 2003 to 2018.1

The study authors focused on fine particles called PM2.5 due to their small size at under 2.5 microns, which allows them to penetrate deep into the lungs and cause chronic inflammation, Hystad explained. These particles are released into the air by different combustion sources, including car engines, fireplaces, and coal-fired power plants, according to the study.2

In total, the researchers observed a 5% increase in cardiovascular events for every 10 microgram-per-cubic-meter increase in concentration of PM2.5. Since there have been immense concentrations of PM2.5 recorded across the world, the researchers were able to assess that 14% of all cardiovascular events observed in patients in the PURE study can be attributed to PM2.5 exposure.1

"That's a big number," Hystad said in a press release. "That's a substantial portion of the cardiovascular disease burden."2

The PURE study had chosen countries from low-, middle-, and high-income brackets to address the current gap in research regarding middle and low-income countries. The researchers found that the income bracket of the country did not affect the statistical impact of air pollution on citizens’ health.1

To analyze the data from the PURE study, cardiovascular disease risk factors were assessed in patients, such as smoking status, eating habits, and pre-existing cardiovascular disease. Researchers also considered other factors, including household wealth and use of dirty fuels for indoor cooking, since prior research demonstrated that solid fuel and kerosene use were linked to cardiovascular disease. Other references the researchers considered included whether patients were living in a rural or urban area, as well as their general access to their country’s health care.1

The study was conducted over a 15-year period, with the participants followed over a period of approximately 9 years. In total, 9152 participants had cardiovascular disease events, including 4083 heart attacks and 4139 strokes. Ultimately, the researchers found 3219 deaths that were attributable to cardiovascular disease.1

The results showed that of the cardiovascular disease events observed, strokes had the strongest association with air pollution exposure. According to Hystad, an increasing number of studies have been able to a show a connection between the risk of stroke and exposure to PM2.5, especially at high concentrations.2

Although the researchers saw that some countries were able to improve the levels of pollution over the 15-year period, they also found that other countries’ levels worsened, according to the study. Hystad explained that in the United States, for example, air pollution was very different in the 1970s compared with now, in part due to the Clean Air Act of 1963.2

"What I hope—and this is actually what is happening—is that developing countries can take these lessons and apply them and reduce the time it takes to achieve some of these air pollution reduction successes," Hystad said in a press release. "Maybe instead of 30 years, you can do it in 10 years.”2

REFERENCES
  1. Hystad P, Larkin A, Rangarajan S, et al. Associations of outdoor fine particulate air pollution and cardiovascular disease in 157 436 individuals from 21 high-income, middle-income, and low-income countries (PURE): a prospective cohort study. The Lancet Planetary Health. 2020;4(6):e235. doi: 10.1016/S2542-5196(20)30103-0.
  2. Air pollution major risk for cardiovascular disease regardless of country income [news release]. Oregon State University; June 23, 2020. sciencedaily.com/releases/2020/06/200623145400.htm. Accessed June 29, 2020.