Air Pollution Cutoff Could Help Shape Preventive CVD Policies

A newly identified threshold for exposure to particulate matter could help public health officials base air-quality warnings on the cardiovascular health risks associated with short-term exposure to poor-quality air.

In a systematic review and meta-analysis of 100 epidemiologic studies from 28 countries, Chinese investigators isolated an optimal alert value of 136 µg/m³—a global average—which they say could prevent 73.2% of cardiovascular deaths attributable to short-term exposure to air pollution. They say about 60,000 deaths in 2023 were related to CV events caused by short-term daily exposures to PM_2.5 pollution at 75 µg/m³ greater.

Study investigator Tao Xue, PhD (Peking University Health Science Centre, Beijing, China), told TCTMD that the findings, published last week in JACC, provide a data-driven analytical framework for policymakers to potentially conduct similar analyses tailored to their country and to air pollution-sensitive diseases.

Xue and colleagues believe the information is applicable to clinical practice.

“Our study identified a supralinear exposure-response relationship, revealing a critical ‘tipping point’ at approximately 150 µg/m³. While the optimal alert value of 136 µg/m³ we calculated is primarily a population-level assessment designed for public health efficiency, the 150 µg/m³ threshold holds significant clinical relevance,” Xue noted in an email. “When daily concentrations exceed this level, the risk for acute CVD events accelerates sharply.

“Clinicians can use this specific threshold to personalize recommendations, prioritizing targeted prevention and proactive communication for their high-risk patients during severe pollution spikes,” he suggested.

In their paper, the researchers say the supralinear pattern “implies that the cardiovascular risk per unit of pollution is not static.” Rather, it “suggests heightened population vulnerability at lower concentrations and an accelerating, severe impact during extreme pollution events,” they explain.

In an accompanying editorial, María Neira, MD, MPH (World Health Organization, Geneva, Switzerland), agrees that an important contribution of the research is the understanding that the harm associated with pollution is not linear.

“Most air-quality alert systems still use broad categories, often derived from legacy standards or political negotiations, rather than from updated epidemiologic evidence,” Neira writes. “This is where the study’s policy implications become particularly relevant.”

The findings can be useful in strengthening alert systems by setting one threshold for the general population and a more protective one for vulnerable groups, she says. Air pollution forecasting should be integrated into care management for high-risk patients, she adds, with physicians encouraging patients to use “personal protective measures (eg, reducing outdoor exertion, air purification, medication management) during forecasted peaks.”

Air pollution is, Neira says, “in many ways, the new tobacco: a massive, preventable cardiovascular risk.”

Considerations in Practice

Over the last decade, evidence has been growing around the contribution of long-term exposure to fine particulate matter (PM_2.5) to CVD morbidity and mortality, with recent research suggesting that the problem needs to be better recognized and addressed by the cardiology community. Much less is known about the risks associated with short-term exposures.

Led by Yongkang Yang, MPH (Peking University Health Science Centre), and colleagues, the researchers note that while high pollution days are infrequent, “they contribute a stable approximately 20% of the total burden of PM_2.5-attributed cardiovascular mortality.”

Between 2000 and 2023, they found that the global burden of CV death attributable to short-term PM_2.5 exposure, beyond what the World Health Organization says is acceptable, nearly tripled from 184,757 to 345,164. Additionally, two major hot spots were identified in the analysis as being outliers in PM_2.5 attributable burden: the North China Plain in East Asia and the IndoGangetic Plain in South Asia. The authors say this “reflects the compounded impacts of extreme air pollution and high population density.”

Even during periods when formal air-quality alerts are not issued, the researchers say they urge clinicians to consider whether short-term spikes in PM_2.5 greater than 100 to 150 µg/m³ justify proactive communication with their high-risk patients.

It’s really all a trade-off of how many alerts can we do and how effective are the alerts. Sadeer Al-Kindi

Commenting for TCTMD, Sadeer Al-Kindi, MD (Houston Methodist DeBakey Heart & Vascular Center, TX), said having a threshold that can be optimized and used on a daily scale is an important first step, with some caveats.

With about half of the studies in the analysis being from China, the threshold does need to be heavily considered in the context of the local area where it is employed.

“I think it’s a reasonable first step, evidence-based approach to understanding the cutoff globally,” Al-Kindi noted. “But the other thing which is important is that this is a continuous risk. There’s no specific safe threshold. So, it’s really all a trade-off of how many alerts can we do and how effective are the alerts. Without  knowing [that] we can’t really decide on a specific threshold, in my opinion, because if you go lower you’ll capture more, but maybe people will get alert fatigue and they just don’t follow the alerts.”

He added that it also bears considering whether the threshold for risk of exposure differs by the source of the air pollution, such as smog and industrial pollutants versus wildfire smoke.

While pollution is becoming more of a talking point in cardiology circles, lack of education on the subject in medical schools and residency limits that knowledge unless people get proactive about it.

That deficit is compounded by US-based policy initiatives, including a decision last week by the Environmental Protection Agency to loosen restrictions on coal-burning power plants that release heavy metals into the air and further limit the scope of the Clean Air Act.

But Al-Kindi said despite all this, cardiologists can help educate patients about the connection between air pollution and CVD. They also can empower them to make their own decisions about exposures and personal protection while the evidence base continues to grow, hopefully in a way that provides practical public health protections for those at greatest risk.

“Are we there yet? No. But are we heading there? Yes,” he added. “I think this is one of the studies that will help us create evidence-based alerts that also take into account patient preferences, cultural practices, and needs while improving cardiovascular health.”