About 15 per cent of deaths worldwide from COVID-19 may be linked to long-term exposure to air pollution, according to a study published on Tuesday.
Researchers, including those from Max Planck Institute for Chemistry, Germany, found that in Europe the proportion of COVID-19 deaths linked to air pollution was about 19 per cent, in North America it was 17 per cent, and in East Asia about 27 per cent.
The study, published in the journal Cardiovascular Research, is the first to estimate the proportion of deaths from the coronavirus that could be attributed to the exacerbating effects of air pollution for every country in the world.
The team noted that these proportions are an estimate of the fraction of COVID-19 deaths that could be avoided if the population were exposed to lower counterfactual air pollution levels without fossil fuel-related and other anthropogenic -- caused by humans -- emissions.
This attributable fraction does not imply a direct cause-effect relationship between air pollution and COVID-19 mortality, the researchers said.
Instead it refers to relationships between two, direct and indirect, i.e. by aggravating co-morbidities, or other health conditions, that could lead to fatal health outcomes of the virus infection, they said.
The researchers used epidemiological data from previous US and Chinese studies of air pollution and COVID-19 and the SARS outbreak in 2003, supported by additional data from Italy.
They combined this with satellite data showing global exposure to polluting fine particles known as 'particulate matter' that are less than or equal to 2.5 microns in diameter (known as PM2.5), information on atmospheric conditions and ground-based pollution monitoring networks.
The researchers created a model to calculate the fraction of coronavirus deaths that could be attributable to long-term exposure to PM2.5.
The results are based on epidemiological data collected up to third week in June 2020 and the researchers say a comprehensive evaluation will need to follow after the pandemic has subsided.
Estimates for individual countries show, for example, that air pollution contributed to 29 per cent of coronavirus deaths in the Czech Republic, 27 per cent in China, 26 per cent in Germany, 22 per cent in Switzerland, and 21 per cent in Belgium.
"Since the numbers of deaths from COVID-19 are increasing all the time, it's not possible to give exact or final numbers of COVID-19 deaths per country that can be attributed to air pollution," said Professor Jos Lelieveld from Max Planck Institute for Chemistry.
"However, as an example, in the UK there have been over 44,000 coronavirus deaths and we estimate that the fraction attributable to air pollution is 14 per cent, meaning that more than 6,100 deaths could be attributed to air pollution," Lelieveld said.
"In the US, more than 220,000 COVID deaths with a fraction of 18 per cent yields about 40,000 deaths attributable to air pollution," he said.
Professor Thomas Munzel from the Johannes Gutenberg University in Germany noted that when people inhale polluted air, the very small polluting particles, the PM2.5, migrate from the lungs to the blood and blood vessels, causing inflammation and severe oxidative stress, which is an imbalance between free radicals and oxidants in the body that normally repair damage to cells.
"This causes damage to the inner lining of arteries, the endothelium, and leads to the narrowing and stiffening of the arteries. The COVID-19 virus also enters the body via the lungs, causing similar damage to blood vessels, and it is now considered to be an endothelial disease," Munzel said.
"If both long-term exposure to air pollution and infection with the COVID-19 virus come together then we have an additive adverse effect on health, particularly with respect to the heart and blood vessels, which leads to greater vulnerability and less resilience to COVID-19," he said.