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  • Jo Waters — United Kingdom

At the heart of air pollution

Air pollution is an invisible threat to human health as well as the planet—and not only because of its connection with respiratory diseases. Research shows air pollution is associated with cardiovascular disease and causes a staggering one in five heart attacks. How can we clean up the air we breathe to save more lives?

When most of us think about the risk factors for a heart attack, it’s probably smoking, high blood pressure and being overweight that first spring to mind. But there’s another hidden and universal threat to our cardiovascular health: the polluted air that nine out of 10 people in the world are currently breathing. Air pollution is estimated to kill seven million people each year, affecting every organ of the body. The risk of respiratory diseases is well understood, but the connection between heart disease and exposure to air pollution has gained traction only recently even though it’s believed to cause 3.5 million deaths globally every year.

Newly updated World Health Organization (WHO) Global Air Quality Guidelines published in September 2021 provide mounting evidence of the damage air pollution inflicts on human health and set ambitious new targets for reducing levels of key air pollutants like particulate matter (PM), ozone, nitrogen dioxide, sulphur dioxide and carbon monoxide. PM is of particular concern for heart health and is generated from fuel combustion from traffic, energy, households, industry and agriculture. Fine concentrations of PM2.5 and PM10 are especially hazardous, with PM2.5 capable of entering the bloodstream and affecting the cardiovascular and respiratory systems.

The growth of urbanisation and more mega cities—with large amounts of traffic and industrial pollution alongside densely populated areas—is accelerating the problem of air pollution. India is home to 35 of the world’s most polluted cities with the highest levels of PM2.5, and the others are found in China, Bangladesh and Pakistan. “Air pollution is a threat to health in all countries but hits people in low- and middle-income countries (LMICs) the hardest,” says WHO Director-General, Dr Tedros Adhanom Ghebreyesus.

Dr Sophie Gumy, team lead on ambient air pollution at the WHO, says air pollution is now considered the largest environmental threat to health—and a significant risk to heart health. “Air pollution from particulate matter affects almost every organ in the body, but mostly respiratory and cardiovascular systems.”

Caused by air pollution

A recent World Heart Federation (WHF) report reveals that more than 20% of all cardiovascular disease (CVD) deaths worldwide are caused by air pollution. Of the seven million deaths worldwide from indoor and outdoor air pollution, 34% are from ischaemic heart disease (heart problems caused by narrowed arteries that supply blood to the heart muscle) and 20% from stroke. The report says the evidence for impact on cardiovascular disease is most consistent for PM, particularly PM2.5 and PM10, although nitrogen dioxide is also believed to play a role. Yet the authors highlighted that there is “still limited understanding among specialist physicians and cardiologists of the importance of air pollution contributing to premature cardiovascular death.”

Professor Michael Brauer, chair of the WHF Air Pollution Expert Group from the University of British Columbia in Canada and the Institute for Health Metrics and Evaluation in the US, and one of the report’s authors, says outdoor air pollution is responsible for eight per cent of all deaths globally. “While it’s quite well recognised that air pollution causes lung disease, it’s not so well recognised that it also causes heart disease, even among many cardiologists,” says Professor Brauer.

Dr David Carbalho, a cardiologist at University Hospital of Geneva and spokesperson for the European Society of Cardiology, agrees with the report’s authors: “Knowledge of the impact of air pollution on cardiovascular health, although scientifically established, remains certainly underestimated by a significant proportion of general and specialised physicians as well as by other healthcare professionals.”

Brauer warns that if we’re to reduce cardiovascular disease deaths around the world, we need to consider pollution. If it’s ignored, many of the advances we’ve made in prevention and treatment of CVD are in danger of being eroded. “Unlike a lot of approaches to diseases—[as] we know how to solve this one—we’re not looking for a miracle cure. We have examples from many countries in the world now where air quality has been improved and mortality reduced,” says Brauer.

We’re not looking for a miracle cure. We have examples from many countries in the world now where air quality has been improved and mortality reduced

Spreading to the heart

PM2.5 poses the biggest danger to the cardiovascular and circulatory system. “There are several mechanisms involved,” says Brauer. “One of those is that PM2.5 causes inflammation in the lungs and this spreads into the bloodstream causing systemic inflammation that affects the heart and arteries and other organs.” Ozone also has an indirect effect on CVD. “[It’s] is a very powerful reactive pollutant and essentially it destroys lung tissue,” says Brauer. “If your lungs are compromised, you’re not able to move as much oxygen into the body, [which] puts a strain on the heart.” Plus, nitrogen dioxide is thought to affect the body’s immune responses to respiratory infection—which is particularly relevant to covid-19—and “can put a strain on the whole body including the heart”.

Dr Mark Miller, a senior research scientist at the British Heart Foundation Centre of Cardiovascular Sciences at the University of Edinburgh, was a member of a team of scientists who discovered how inhaled particles pass from the lungs and into the bloodstream in a key 2017 breakthrough. “PM damages blood vessels, causes irregular heart rhythms and increases the risk of blood clots,” says Miller. “These actions would increase the chances of someone developing heart or circulatory disease. “Our team were the first to establish that tiny particles the size of diesel exhaust particles can be inhaled and cross over from the lungs into the bloodstream. The particles then build up in fatty plaques in the arteries, where they could possibly trigger a heart attack or stroke.”

Benefitting from reduced pollution

There is now an extensive evidence base to show that cutting air pollution results in reductions in mortality and a decrease in healthcare costs, says Professor Dean Schraufnagel, a professor of medicine and pathology at the University of Illinois in Chicago, who published a 2019 paper detailing the benefits. “Studies have shown important health improvements came after the Clean Air Act was passed in the United States in 1970,” he says. “The improved air quality tracked with decreases in several diseases and death rates. This occurred in conjunction with an economic growth of 259%, so it’s clear you can decrease air pollution and increase country wealth at the same time.”

Professor Schraufnagel says these health improvements can come quickly too, especially for cardiovascular health. “When Ireland banned smoking in indoor public places, ischaemic heart disease was reduced by 26% within weeks.” Other success stories include a 1990 restriction on the sulphur content of fuel oil used for power plants and motor vehicles in Hong Kong, which led to a 45% drop in ambient sulphur dioxide concentrations. A study found this intervention led to a decline in the annual rates of all-cause mortality (2.1%), respiratory mortality (3.9%) and cardiovascular mortality (2.0%), improving life expectancy by 20 days for women and 41 days for men.

The dramatic impact of covid-19 lockdowns on air pollution and the likely health benefits is another area of interest for future research.

Industrialisation versus health gains

However, Schraufnagel says improving air quality may be harder to achieve in low-income countries (LICs) where industrialisation is seen as key to alleviating poverty. But he says health gains will be even greater in countries with the highest levels of pollution. “The pollution problems of India are daunting, with urban population growth of 31.8% and overall population growth of 17.6% between 2001 and 2011,” he says. “But the national government, as well as several cities, have put into place a broad range of policies to halt pollution and expand green space.”

Some of the interventions include developing and monitoring air pollution standards, emissions testing, travel restrictions, increased taxes on and removal of subsidies from polluting sources, increased use of clean energy, and restriction of burning biomass fuels. Brauer says Mexico City now has far cleaner air than in the 1980s and even China has turned the corner: “Although China still has high levels of pollution, levels have been going down since 2012-13 due to using less coal and using cleaner sources of energy, cleaning up the dirtier sources, more motor vehicle regulation, and banning the burning of coal in and around major cities.”

The impact of air pollution on cardiovascular health remains underestimated by a significant proportion of healthcare professionals

Gumy from the WHO warns the global air pollution situation is grave, but says because the causes are multi-factorial there is no one-size-fits-all quick fix: “There is a need to adapt and change energy policies—towards renewable energies and targeted fossil fuel subsidies—transport policies, the way we envisage mobility, land-use policies, the way cities are built, waste management, agriculture practices and also the way we consume. “The overall message is [to reduce] fossil fuels combustion. Adopting air quality standards and enforcing them is indeed critical to successfully achieve better air quality.”

The scale of the threat to heart health was acknowledged by the European Society of Cardiology in new guidelines in 2019 that ranked air pollution as the second biggest risk factor for a heart attack after smoking—more important than blood pressure, sedentary lifestyle or raised cholesterol. Professor Brauer says awareness of the connection between air pollution and heart health is an ongoing challenge. Indeed, very few people have air pollution written on their death certificate. “It’s very easy for a cardiologist to ask patients about their diet, exercise and smoking, and give advice accordingly, but not so easy to ask about air pollution exposure—that’s a really difficult question to answer,” says Brauer.

But if health professionals and organisations like the WHF can get the message out, the benefits have the potential to be widespread and less dependent on individual lifestyle changes that are typically associated with a reduction in CVD risk. “A lot of preventative health measures such as smoking cessation are at an individual level, but if you improve air quality, everyone benefits without having to actually do anything except carry on breathing,” says Brauer.

HIGHROAD TO CHANGE There is much that can be done at personal, national and global levels to combat air pollution

Future focus

Schraufnagel says there’s more to be done at the personal, national and global levels to combat air pollution. “For instance, there is a group of school-run mothers in London who have been running an anti-idling traffic campaign to encourage parents doing drop-offs and picks-ups to turn off their engines so children are not exposed to car exhaust emissions. What could be simpler than just turning off their ignitions?”

Cooking with an open fire could be replaced with a non-polluting stove, he says. The Clean Cooking Alliance works with a global network of partners to promote clean cooking technologies in LMICs, with the goal of achieving universal access to clean cooking by 2030. Schraufnagel says exercising a few streets back from a main throughfare could significantly reduce exposure to PM, while mask wearing and air purifiers may also be beneficial.

He also recommends national policy makers introduce polices such as air quality monitoring, low emission zones and pedestrianised areas. “The car industry is also switching to electric cars quite rapidly now and coal power plants are moving over to cleaner fuels such as natural gas,” says Schraufnagel. “Tackling air pollution and climate change really go hand in hand.” Above all, says Gumy from the WHO, “advocacy, science-based communication and multisectoral and coordinated action are key.” •


ILLUSTRATION – Luke Best – GRAPHICS – Trine Natskår


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