Air Pollution Exposure Linked to Increased Risk of Hospitalization for Seniors

Yaguang Wei, PhD

Credit: Harvard University

Older adults with chronic exposure to fine particulate air matter with an aerodynamic diameter of ≤ 2.5 (PM_2.5)—a major element of air pollution—may have an increased risk for cardiovascular hospitalization, a new study found.¹

The Environmental Protection Agency (EPA) announced its updated National Ambient Air Quality Standards on February 7th, lowering the country’s acceptable mean annual PM_2.5 level from 12 μg/m³ to 9 μg/m³.

“The timing of our study couldn’t be more critical, and its implications are profound,” said lead investigator Yaguang Wei, PhD, research associate in the Department of Environmental Health at Harvard, in a press release.² “Our findings quantify the benefits of implementing stricter air pollution control policies—even stricter than the Environmental Protection Agency’s new standards, which are considerably higher than the 5 micrograms per cubic meter standard set by the World Health Organization.”

When the tiny particles are inhaled by the lungs, they can enter the bloodstream and cause an array of problems from systematic inflammation to cardiac electrical changes.¹ Investigators conducted a population-based study to assess the association between chronic exposure to fine PM_2.5 and the risks of hospitalization for major onset cardiovascular disease subtypes.

The study included 59,761,494 Medicare fee-for-service beneficiaries aged ≥ 65 years during the years 2000 – 2016. Wei and colleagues assessed the risk of first hospital admission during follow-up for ischemic heart disease, cerebrovascular disease, heart failure, cardiomyopathy, valvular heart disease, thoracic and abdominal aortic aneurysms, or a compilation of several of these cardiovascular disease subtypes.

Most of the sample were White (84.3%), female (55%), and aged 65 – 74 years at baseline (75.1%). A total of 17.6% of the participants enrolled in Medicaid at some point during the study.

The team linked adjusted predicted PM_2.5 levels with participants’ zip codes to estimate the exposure of individuals to PM_2.5 levels at each participant’s residence as a substitute for actual exposure measurements. Due to estimations, investigators used a casual framework against confounding bias and bias due to exposure measurement errors.

In total, hospital admissions of the beneficiates were related to composite CVD (21.8%), ischemic heart disease (8.8%), cerebrovascular disease (7.7%), heart failure (6.6%), and arrhythmia (6.5%).

Participants exposed to mean PM_2.5 exposure were linked to increased relative risks in hospitalizations for ischemic heart disease, cerebrovascular disease, heart failure, cardiomyopathy, arrhythmia, and thoracic and abdominal aortic aneurysms.

The exposure-response curve for compositive CVD showed a “monotonically increased risk” linked to PM_2.5. For compositive CVD, the relative risk at exposures between 9 and 10 µg/m³ was 1.29 (95% confidence interval [CI], 1.28 – 1.30). In comparison, the mean US national exposure was 9.7 µg/m³ during the study period; the World Health Organization air quality guideline recommended an exposure of ≤ 5 µg/m³.

“For the composite CVD outcome, the exposure-response curve monotonically increased, suggesting that no safe threshold exists for overall cardiovascular health,” investigators wrote.

Ischemic heart disease, cerebrovascular disease, heart failure, and cardiomyopathy also monotonically increased, with the heart failure curve having the steepest slope. The relative risk of hospitalization for heart failure was associated with a calibrated lag 0-2PM2.5 concentration ranging from 1.19 (95% CI, CI, 1.17 – 1.22) to 2.31 (95% CI, 2.28 – 2.35).

Using an absolute scale, composite CVD’s hospitalization risk increased from 2.59% with exposures ≤ 5 µg/m³ to 3.35% at exposures between 9 and 10 µg/m³. The risks lasted ≥ 3 years after PM_^2.5 exposure.

The study found age, education, access to healthcare, and neighborhood deprivation level affected exposure levels of PM_2.5. For instance, older adults from socioeconomically deprived neighborhoods had an increased risk for hospitalizations after PM_2.5 exposure.

“At the neighborhood level, we found a higher risk of hospital admission associated with PM_2.5 for beneficiaries living in zip codes with lower rates of high school completion, longer distance to the nearest hospital, or greater neighborhood deprivation,” investigators wrote.

The team highlighted several limitations, including limited available data sources—such as data on potential risk factors such as body mass index or smoking—and the framework not accounting for unobserved confounders. Additionally, they wrote how exposure assessment could have measurement error, and the study cannot be generalized due to the sample only coming from the Medicare population from 2000 – 2016.

“Stronger efforts are urgently needed to improve air quality and thereby alleviate the burden of cardiovascular disease—a leading cause of death and a major contributor to health care costs,” said investigator Joel Schwartz, professor of environmental epidemiology.² “Our findings indicate that the EPA’s newly updated PM_2.5 standard is clearly insufficient for the protection of public health.”

^References

1. ^{Wei Y, Feng Y, Danesh Yazdi M, et al. Exposure-response associations between chronic exposure to fine particulate matter and risks of hospital admission for major cardiovascular diseases: population based cohort study. BMJ. 2024;384:e076939. Published 2024 Feb 21. doi:10.1136/bmj-2023-076939}
2. ^{Chronic Exposure to Air Pollution May Increase Risk of Cardiovascular Hospitalization Among Seniors. EurekAlert! February 21, 2024. https://www.eurekalert.org/news-releases/1034800. Accessed February 27, 2024.}