Exposure to Air Pollution in China Tied to Increase in Coronary Calcium

People who live in areas with higher levels of air pollution appear to have a heavier burden of coronary artery calcification (CAC), a cross-sectional study out of China indicates.

Increases in exposure to multiple pollutants, especially fine particulate matter and nitrogen dioxide, were related to higher CAC scores and greater likelihoods of having any calcium or severe CAC (Agatston score > 400).

“Given that CAC is strongly associated with total [coronary heart disease (CHD)] events, coupled with the recently reported finding that higher long-term PM_2.5 exposure was associated with a higher risk of CHD mortality in China, this study may provide evidence suggesting that coronary atherosclerosis is a pathological pathway through which air pollution exposure potentially increases mortality associated with CHD,” lead author Meng Wang, PhD (University at Buffalo, NY), and colleagues write in their paper published online June 28, 2019, in JAMA Network Open.

Co-author Matthew Budoff, MD (Harbor UCLA Medical Center, Torrance, CA), noted that prospective US data—from the MESA Air study—have also shown relationships between air pollution and CAC, albeit of somewhat weaker magnitudes.

Obviously we need to do more to deal with the air pollution issue. Matthew Budoff

That this look at China, which has much higher levels of air pollution compared with the United States, reveals stronger-than-expected associations “speaks to the gravity of the problem, especially as more cities are having increasing levels of air pollution,” Budoff told TCTMD. “We really need to think about that as a direct cause. We always think about asthma and lung cancer, other health problems, but I think we have to think of heart health as well.”

A growing amount of data supports that link between exposure to air pollution and cardiovascular disease risks, although the mechanisms are not entirely clear. Wang et al say that an effect on atherosclerosis is a likely pathway. “If an association between air pollution and subclinical atherosclerosis were established, it could provide an opportunity to intervene before disease is manifested clinically by way of community-level efforts to control pollution exposures,” they write.

Data on Nearly 9,000 People

To explore that concept, the investigators examined baseline data from the prospective CREATION cohort in China, a country with high levels of air pollution. The analysis included 8,867 consecutive patients (mean age 57 years; 54% men) who underwent calcium scans for suspected CHD at Fuwai Hospital in Beijing. Mean CAC score was 91.4 Agatston units.

The researchers took advantage of a network of more than 1,400 monitoring stations set up in China in response to growing concerns about air pollution to estimate annual means of the following types of exposures at participants’ residences: fine particulate matter with an aerodynamic diameter of less than 2.5 µm ( PM_2.5), nitrogen dioxide, and ozone. They also determined traffic exposure by calculating proximity to nearby roadways.

All exposures were associated with CAC burden, although the relationships were strongest for PM_2.5 and nitrogen dioxide. CAC scores increased by 27.2% for every 30-µg/m3 increase in PM_2.5 and by 24.5% for every 20-µg/m3 increase in nitrogen dioxide. Moreover, greater exposure to air pollution was associated with increased likelihoods of any CAC and severe CAC.

In general, the observed associations were stronger in men, people older than 60, and those with diabetes.

Budoff said he and the other researchers were surprised by the strengths of the relationships, which, as they explain in their paper, “were likely more apparent than those in prior studies owing to the very broad range of ambient air pollution concentrations we observed. In addition, this is a population at risk for coronary atherosclerosis.”

The link between levels of air pollution and subclinical atherosclerosis is likely causal, Budoff suggested, pointing to the supportive prospective US data. Several potential mechanisms are being explored, including effects on lipids, direct toxicity to cell walls, and inflammation.

Nonetheless, “obviously we need to do more to deal with the air pollution issue,” Budoff said, noting that it is a growing problem in some parts of the US. “There are many cities in the US that are seeing a pretty dramatic rise, and I think if it impacts both the number one cause of death, which is heart disease, and the number two cause of death, which is lung cancer, then we have double the motivation to address this problem.”