Air pollution linked to increase in hospital admissions for serious heart and lung conditions

Short- and long-term exposure to fine particulate matter (PM_2.5) air pollution is linked to an increased risk of hospitalization for major heart and lung diseases, according to two large American studies published by The BMJ Today.

Together, the findings suggest that there is no safe threshold for heart and lung health.

According to the Global Burden of Disease study, exposure to particulate matter_2.5 accounts for approximately 7.6% of total global mortality and 4.2% 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 air quality guidelines in 2021, recommending that an annual average of PM_2.5 levels should not exceed 5 μg/m³ and average over 24 hours p.m._2.5 levels should not exceed 15 μg/m³ more than 3 to 4 days per year.

In the first study, researchers linked average daily PM_2.5 levels in residential ZIP codes for nearly 60 million U.S. adults (84% white, 55% female) ages 65 and older from 2000 to 2016. They then used Medicare insurance data to track the hospital admissions over an average of eight years.

After taking into account a series of economic, health and social factors, the average particles_2.5 three-year exposure was associated with an increased risk of first hospitalization 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 to exposures of 5 μg/m³ or less (WHO air quality guidelines for annual particulate matter_2.5), exposures between 9 and 10 μg/m³which encompassed the US national average of 9.7 μg/m³ during the study period, were associated with a 29% increased risk of hospitalization for cardiovascular disease.

In absolute scale, the risk of hospitalization for cardiovascular disease increased from 2.59% with exposures to 5 μg/m³ or less than 3.35% at exposures between 9 and 10 μg/m³. “This means that if we managed to reduce annual particulate matter_2.5 below 5 µg/m³“, we could avoid 23% of hospitalizations for cardiovascular diseases,” say the researchers.

These cardiovascular effects persisted for at least three years after exposure to particles._2.5and susceptibility varied by age, education, access to health care services and level of deprivation in the area.

The researchers say their results suggest that there is no safe threshold for the chronic effect of particles._2.5 on overall cardiovascular health and that substantial benefits could be achieved through adherence to WHO air quality guidelines.

“On February 7, 2024, the U.S. Environmental Protection Agency (EPA) updated the National Air Quality Standard for annual particulate matter._2.5 level, setting a stricter limit at no more than 9 µg/m³. This is the first update since 2012. However, it remains significantly higher than 5 µg/m³ set by the WHO. Clearly, the newly published national standard was not sufficient to protect public health,” they add.

In the second study, researchers used daily PM at the county level._2.5 concentrations and medical claims data to track hospital admissions and emergency department visits for natural causes, cardiovascular disease, and respiratory disease for 50 million U.S. adults ages 18 and older from 2010 to 2016.

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

They found that short-term exposure to particles_2.5even at concentrations below the new WHO recommended limit for air quality, was statistically significantly associated with higher rates of hospitalizations for natural causes, cardiovascular and respiratory diseases, as well as emergency room visits for respiratory illnesses.

For example, on days when the daily afternoon_2.5 levels were below the new WHO air quality guidelines limit of 15 μg/m³an increase of 10 μg/m³ in PM_2.5 was associated with 1.87 additional hospitalizations per million adults aged 18 and older per day.

The researchers say their findings are an important contribution to the debate on revising air quality limits, guidelines and standards.

Both research teams acknowledge several limitations, such as possible misclassification of exposure, and point out that other unmeasured factors may have affected their results. Additionally, the results may not apply to people without health insurance, children and adolescents, and those living outside the United States.

However, taken together, these new results provide a valuable benchmark for future national air pollution standards.