Studies show no safe air quality threshold exists for heart & lung health

New York: Short and long term exposure to fine particulate matter (PM2.5) air pollution is linked to an increased risk of hospital admission for major heart and lung diseases, find two large US studies, published by The BMJ on Thursday.

Together, the results suggest that no safe threshold exists for heart and lung health, said the team of researchers from Harvard T.H Chan School of Medicine, US.

According to the Global Burden of Disease study, exposure to PM2.5 accounts for an estimated 7.6 per cent of total global mortality and 4.2 per cent of global disability adjusted life years (a measure of years lived in good health).

In light of this extensive evidence, the World Health Organization (WHO) updated the air quality guidelines in 2021, recommending that an annual average PM2.5 levels should not exceed 5 microgram per cubic metre and 24 hour average PM2.5 levels should not exceed 15 microgram per cubic metre on more than 3-4 days each year.

In the first study, researchers linked average daily PM2.5 levels to residential zip codes for nearly 60 million US adults (84 per cent white, 55 per cent women) aged 65 and over from 2000 to 2016.

They then used Medicare insurance data to track hospital admissions over an average of eight years.

After accounting for a range of economic, health and social factors, average PM2.5 exposure over three years was associated with increased risks of first hospital admissions for seven major types of cardiovascular disease -- ischemic heart disease, cerebrovascular disease, heart failure, cardiomyopathy, arrhythmia, valvular heart disease, and thoracic and abdominal aortic aneurysms.

Compared with exposures of 5 microgram per cubic metre or less (the WHO air quality guideline for annual PM2.5), exposures between 9 and 10 microgram per cubic metre, which encompassed the US national average of 9.7 microgram per cubic metre during the study period, were associated with a 29 per cent increased risk of hospital admission for cardiovascular disease.

On an absolute scale, the risk of hospital admission for cardiovascular disease increased from 2.59 per cent with exposures of 5 microgram per cubic metre or less to 3.35 per cent at exposures between 9 and 10 microgram per cubic metre.

“This means that if we were able to manage to reduce annual PM2.5 below 5 microgram per cubic metre, we could avoid 23 per cent in hospital admissions for cardiovascular disease,” said the researchers from the Havard University in the US.

These cardiovascular effects persisted for at least three years after exposure to PM2.5, and susceptibility varied by age, education, access to healthcare services, and area deprivation level.

The researchers said their findings suggest that no safe threshold exists for the chronic effect of PM2.5 on overall cardiovascular health, and that substantial benefits could be attained through adherence to the WHO air quality guideline

In the second study, researchers used county-level daily PM2.5 concentrations and medical claims data to track hospital admissions and emergency department visits for natural causes, cardiovascular disease, and respiratory disease for 50 million US adults aged 18 and over from 2010 to 2016.

During the study period, more than 10 million hospital admissions and 24 million emergency department visits were recorded.

They found that short term exposure to PM2.5, even at concentrations below the new WHO air quality guideline limit, was statistically significantly associated with higher rates of hospital admissions for natural causes, cardiovascular disease and respiratory disease, as well as emergency department visits for respiratory disease.