Almost 70% of the 4.2 million deaths attributed to ambient (outdoor) air pollution in 2019 were caused by cardiovascular diseases, notably ischaemic heart disease (1.9 million deaths) and stroke (900,000 deaths), according to a new report by the World Heart Federation (WHF).

The report highlights the outsized impacts air pollution is having on the worldwide epidemic of cardiovascular diseases (CVDs).

Meanwhile, air pollution has become the leading risk factor for global disease burden, overcoming even hypertension, according to a recently published Lancet study, in a ranking of 88 environmental and health risk factors across 204 countries and territories. The analysis was a part of the Global Burden of Disease (GBD) study 2021, conducted by the Seattle-based Institute of Health Metrics and Evaluation (IHME).

The GBD study is published once every two years but publication of the 2021 data was delayed until now, due to the pandemic. It considered risk factors ranging from environmental and occupational hazards, such as air pollution, to behavioural factors such as tobacco use, physical inactivity, unsafe sex and poor nutrition.

Air pollution was also one of the leading risk factors in the last GBD study published in 2020, but as the disease burden was calculated separately for ambient and household pollution, which have overlapping mortality, it did not rank as the highest.

But in the 2021 Lancet report, malnutrition risk factors, largely related to low birth weight, child growth failure and suboptimal breastfeeding were ranked separately. If those were ranked together, then malnutrition [primarily neonatal, newborn and early childhood] becomes the Number 1 risk, with air pollution, second and hypertension third, said Michael Brauer, lead author of the study for the Institute for Health Metrics and Evaluation (IHME), in a comment to Health Policy Watch.

Cardiovascular – not lung disease – associated with the lion’s share of air pollution-related deaths

However, among the diseases most closely associated with ambient (outdoor) air pollution-related exposures, cardiovascular disease is responsible for the lion’s share according to the new WHF report. And that is a striking new finding.

“Most people, when they think of air pollution they think of someone coughing, they think of lung conditions like asthma and pulmonary disease. But actually, it is the cardiovascular conditions which are probably the most concerning,” Dr Mark Miller of the University of Edinburgh, and the WHF’s Chair of the Air Pollution and Climate Change Expert Group told Health Policy Watch.

“This report essentially is like a reappraisal of the most recent World Health Organization (WHO) data to emphasize how bad the cardiovascular effects of air pollution are,” he said.

The report titled ‘Clearing the Air to Address Pollution’s Cardiovascular Health Crisis’ was launched during the World Heart Summit underway this weekend in Geneva, Switzerland. It represents one of the most sweeping reports, to date, by the global federation on a risk factor that many cardiologists have failed to fully acknowledge.

In terms of household air pollution – the link to CVD is also clear – if not quite as pronounced.

Amongst the 3.2 million deaths attributed to household air pollution in 2019, 53% was attributable to CVDs – including one million deaths from ischaemic heart disease and 700,000 from stroke.

Seen from the disease perspective, some 37% of all CVD deaths globally were attributable to air pollution in 2019, including 22% of deaths from ischaemic heart disease and 15% from stroke, according to the report.

Air pollution – the greatest single environmental health risk

The report calls air pollution “the greatest single environmental health risk.” In some regions air pollution is over ten times the recommended limit by the WHO, the report noted.

Cardiovascular disease kills more than 20 million people every year globally. Air pollution has the most impact on people with pre-existing cardiovascular conditions, the report said.

The report warned that without adequate policies in place, deaths and disability from cardiovascular conditions caused or worsened by air pollution is set to increase further.

“These two reports highlight how critical it is for governments to prioritise measures to rapidly improve air quality, to save lives and reduce the toll and cost of cardiovascular disease – the world’s biggest killer,” said Nina Renshaw, Head of Health at the Clean Air Fund. “The fact that air pollution is the number one risk factor driving the global burden of disease requires attention from health donors too. Efforts to tackle air pollution remain chronically underfunded, receiving only 1% of global development funding in recent years. Air pollution must quickly become a higher priority in global health.”

Why air pollution is such a CVD killer

In fact, while not intuitive, there are clear physiological reasons why air pollution, and particular fine particulates are so closely associated with heart disease and stroke.

Air pollution particles are absorbed in tissue deep in the lungs where they can cause inflammation setting the stage for chronic lung disease and cancers. But the finest particles, of PM2.5 or smaller in diameter, penetrate the lung walls and enter the bloodstream. Circulating in arteries and veins of the body and the brain, these fine particles exacerbate the build-up of plaque over time, as well as contributing to the constriction of the arteries, setting up a perfect storm of conditions for heart disease and stroke.

Air pollution-related CVD deaths increasing sharply in Southeast Asia and the Eastern Mediterranean 

The report also finds that the number of deaths from heart disease attributable to air pollution has increased in some regions by as much as 27% over the past decade.

A key reason for this is the rising air pollution levels in some countries of Southeast Asia and the Eastern Mediterranean, where average air pollution concentrations are nearly ten times the WHO – recommended levels, experts say.

The Western Pacific region saw the highest number of deaths from heart disease and stroke due to outdoor air pollution with nearly one million deaths in 2019, and the Southeast Asian Region was a close second, with 762,000 deaths.

Countries facing the some of greatest challenges with air pollution include those in the Eastern Mediterranean, with Kuwait, Egypt, and Afghanistan.

Real number of CVD deaths related to air pollution is likely higher

Moreover, the real number of CVD deaths from air pollution is in fact likely to be much higher, as currently, mortality is only assessed for a single air pollutant i.e PM2.5, and only for ischaemic heart disease and stroke, while there are a range of other cardiovascular diseases that may be exacerbated by air pollution.

“The reality is that there is a real lack of reliable and granular data, mostly due to the absence of ground monitoring systems. This is especially true in low-income settings where millions of people live in unmonitored areas,” said Mariachiara Di Cesare from the University of Essex who was involved with the WHF’s report.

“To give an example, IQAir’s 2023 World Air Quality Report provides a comprehensive overview of PM2.5 data across almost 8,000 cities in 134 countries, regions, and territories. When you look at Africa out of 54 African countries, only 24 have the capacity to monitor air quality in some capacity, with most of the existing stations concentrated in the western and southern regions of the continent,” Di Cesare said.

This makes the results of the report an underestimate, Cesare told Health Policy Watch. She said that improved air pollution monitoring in both rural and urban areas will help provide more accurate estimates of air pollution levels and trends.  

WHF study relies upon 2019 data – Lancet updates that air pollution is now the top killer

Significantly, the new WHF report relies upon 2019 data regarding air pollution impacts on cardiovascular health. The latest IHME Global Burden of Disease study, published in The Lancet, provides slightly updated data – linked to 2021. Also, the WHF report focuses its analysis primarily on air pollution related CVD deaths, while the Lancet study looks at both mortality and morbidity. But the overall message regarding the killer impacts of air pollution is the same.

Over 11,000 researchers were part of the IHME GBD study. Following air pollution, high blood pressure and smoking were the second and third-ranking risk factors contributing to excess disease and disability – or Disability Adjusted Life Years (DALYS). However, if all of the dozen or so

“These are groups of risk factors where the exposure to the risk factors is increasing. And then, that is exacerbated by these demographic factors, the growing populations, the aging populations,” said Brauer in a podcast unpacking the findings.

At the same time, if malnutrition risks are aggregated together, then they become the top risk, with air pollution ranking number 2, Brauer said, noting that the original IHME GBD analysis, upon which The Lancet publication was based, considered several “levels” of aggregation of the risks that were analysed. These malnutrition risks are mainly related to poor maternal, neonatal and early childhood nutrition, including infections from parasitic and water-borne diseases, tuberculosis and other respiratory conditions. Risk factors linked to unhealthy diets, including factors like high red meat consumption, low fruit, vegetables, nuts and seeds; and high salt and sugar intake, ranked fifth in the aggregated analysis.

The 2021 Lancet study also looks at how health risks have evolved over the past two decades – comparing the most recent findings with those in 2000. That was the year that GBD study quantifying deaths and disease linked to a set of 25 environmental, occupational and behavioural health risks was published by the WHO. A comparison between the two shows risk factors that stagnated or become more significant, along with those that have moved down the list as conditions improved, notably for safe water, hygiene and sanitation.

Climate change is compounding impacts

Climate change is also turning out to be an additional stressor, compounding air pollution risks, as global temperature rise continues unabated, the WHF experts note.

This year has already seen heatwaves from Mali to India and temperatures have soared. Climate change has increased the frequency and the intensity of heatwaves, according to climate scientists. Heatwaves are also known to exacerbate underlying non-communicable diseases like diabetes and heart ailments as Health Policy Watch has reported earlier.

“That’s the sort of, that’s the sort of main message that the science is telling us now, as we’re starting to see all these environmental stressors compounding each other,” said Miller. “And you would expect that, for example, if you have heat waves that were accompanied by higher air pollution, that would make cardiovascular disease worse.”

Global air pollution-related healthcare costs are already projected to surge from $21 billion in 2015 to USD 176 billion in 2060, with annual lost working days potentially increasing to 3.7 billion by 2060. Any additional stressor will make the costs worse, the WHF report notes.

The key message, however, is that action will make a difference, Miller said. “While highlighting some really terrifying figures here, these huge numbers of deaths worldwide as well…we’re referring to them as preventable deaths, because air pollution is preventable. So, there’s an opportunity here, as well that, you know, if we can tackle these issues, and we know some of the measures to do so then hopefully, we will see improvements in cardiovascular health.”

–Updated to include reference to “malnutrition” risks and their ranking, as relates to air pollution, in the IHME analysis.

Image Credits: Unsplash, IHME, Clearing the Air to Address Pollution’s Cardiovascular Health Crisis report., Clearing the Air to Address Pollution’s Cardiovascular Health Crisis Report, IHME , Global Burden of Disease Study 2021.