CVD Effects of Wildfire-Related Air Pollution Differ by Event

Air pollution caused by wildfires can raise the risks of cardiovascular events and death, but the impact is inconsistent, according to new data from two major California wildfires.  

Increased risks of both CVD events and all-cause mortality were observed after the Mendocino Complex fire, which burned for 2 months during the summer of 2018, but not after the Camp fire that burned in November of that year, despite the latter being associated with substantially worse air pollution.

The differences between the individual fires surprised researchers.

“Previous studies have shown that the high concentrations of pollution we saw during the Camp fire were not safe,” lead author Stacey E. Alexeeff, PhD (Kaiser Permanente Northern California, Pleasanton), told TCTMD in an email. “And, like the Mendocino Complex fire, the Camp fire spread smoke across the region and led to levels of air quality that were above the daily limit set by the Environmental Protection Agency to protect public health. On one day, the Camp fire was responsible for the worst air pollution in the world.”

The new data have broader public health implications, but they should also be heeded by clinicians, according to senior author Jamal S. Rana, MD, PhD (Kaiser Permanente Oakland Medical Center, Oakland, CA).

“It’s important that clinicians recognize that pollution due to wildfires can increase risk of heart disease,” he told TCTMD in an email. “They can remind patients that it’s important to be aware of air quality and how to find information about air quality in their area online.”

Additionally, Rana said that clinicians can provide education on how masks can offer protection during a fire and remind patients about maintaining prescribed medical therapy.

“When people are facing huge losses or stresses, they may not stick to their daily medication routine,” Rana added. “It’s important to make sure patients are vigilant about taking their medications during these times.”

Mendocino Complex and Camp Fires

The negative cardiovascular effects of air pollution in general—and from wildfires specifically—have been documented. Although researchers are only beginning to understand the specifics with how different particulate matter might trigger adverse outcomes, they have sounded alarms for more awareness and action. With large-scale events like last month’s Los Angeles wildfire storm, the topic has only become more relevant.

“Like so many others living in California, I’ve seen more large wildfires in recent years, bringing smoke and air pollution into the area,” said Alexeeff. “I saw firsthand the choices people had to make about whether to go outside or let their children go outside. Even though we’ve studied air pollution health effects for decades, these new challenges with large wildfires bring a need for new research.”

For the study, published online last week in the Journal of the American Heart Association, the researchers analyzed data from 3.2 million adults (52.2% female; mean age 47 years) within the Kaiser Permanente Northern California healthcare system. The data represented 587.9 million person-days between July and December 2018 following the Mendocino Complex wildfire (July-August) and the Camp wildfire (November).

High particulate matter (> 35 μg/m³) was reported for 4.7 and 35.9 million person-days, respectively, following the Mendocino Complex and Camp fires. The air pollution was significantly associated with risks of acute MI, heart failure, stroke, and CV death (RR 1.23; 95% CI 1.04-1.46) and all-cause death (RR 1.36; 95% CI 1.13-1.64) following the Mendocino Complex fire when compared with study days logged at better levels of particulate matter (< 12 μg/m³).

Researchers did not find similar associations for either CVD events (RR 0.97; 95% CI 0.89-1.04) or all-cause death (RR 0.99; 95% CI 0.90-1.07) following the Camp fire.

In sensitivity analyses, there were strong associations between CVD events and air pollution exposure on the same day as well as 4 days later during the Mendocino Complex fire.

‘Every Wildfire Is Different’

While the study can’t explain why the health effects of the fires differed, Alexeeff suspects “that the people who were most susceptible to wildfire pollution had cardiovascular events triggered by the Mendocino Complex fires, which occurred before the Camp fire. It’s also possible there were different types of materials burning in each fire.”

Also, public awareness of the harmful effects of wildfires increased throughout the year, so people may have been better prepared with masks and other protective measures, she said.

It’s important to make sure patients are vigilant about taking their medications during these times. Jamal S. Rana

“Every wildfire event is different,” said Mark Miller, PhD (University of Edinburgh, Scotland), who commented on the results for TCTMD. The Mendocino Complex fire burned longer, but the Camp fire resulted in more pollution, he noted.

“The air pollution affects different areas, which means that different people are being exposed,” said Miller. “It may be the case that that people in one region are people who have more health conditions, so they’re more vulnerable to air pollution. Sometimes the material burning—it’s not just wood, it’s different materials including people’s homes and things—and that means that the mixture of air pollutants and the type of air pollutants in them are all very different.”

It’s very likely that increasing awareness played into the findings as well, Miller added. “Probably as soon as people got the alert that [the Camp] wildfire [was] in their area, they wore the face masks or they got out of the area quickly.”

Given the “strong science now linking air pollution to cardiovascular health,” Miller said wildfire as a CVD threat needs to be taken seriously. He noted that pollution caused by wildfires affects populations hundreds of miles away from the original event, so he advises clinicians to ask vulnerable patients to consistently check air quality and take precautions when necessary.

Future research, he added, should be aimed at understanding how pollution from wildfires differs from other pollutants and how long the deleterious effects last.

For Alexeeff, “it will be important for us to learn more about how what is burning—whether it’s, say, trees, buildings, plastics, or some combination—affects our health,” she said, adding that looking at the effect of public health measures would also be fruitful. “It would be important to know what actions people took to protect themselves, and how many lives were potentially saved because of public health warnings.”