As reported by PBS, during the first half of July, the world experienced record-breaking heatwaves, with temperatures soaring to unprecedented heights. Simultaneously, CNN reported on the impact of uncontrollable Canadian wildfires and how they extended far beyond national borders, releasing a blanket of smoke that compromised air quality, which triggered health advisories in numerous U.S. states.
As a result, a study published in the American Heart Association’s journal Circulation claims that this perilous combination of scorching heat and suffocating fine particulate pollution could double the risk of death from heart attacks.
The study, which examined over 200,000 heart attack fatalities, found that days characterized by extreme heat, extreme cold, or high levels of fine particulate matter (PM2.4) air pollution were significantly linked to an increased risk of death from heart attacks. This risk was particularly pronounced among women and older adults.
Senior author Yuewei Liu, MD, PhD, an associate professor of epidemiology in the School of Public Health at Sun Yat-sen University in Guangzhou, China, said in a press release,
“Our findings provide evidence that reducing exposure to both extreme temperatures and fine particulate pollution may be useful to prevent premature deaths from heart attack, especially for women and older adults.”
Meanwhile, Loren Wold, PhD, a professor in the division of cardiac surgery at The Ohio State University in Columbus and a researcher and expert in external triggers of cardiac disease, especially air pollution said, “This is a robust study with a large number of participants, which allows us to really see the small changes. It highlights the risk that high temperatures and high particulate levels pose to the heart — and the even greater risk when those are combined.” Notably, Dr. Wold was not involved in this research.
High Temperatures and Pollution Linked to Elevated Risk of Sudden Cardiac Events
Dr. Wold continues, “We’ve known for quite some time that extreme temperature events (ETEs) — and that includes both high temperature swings and low temperature swings — is linked with an increased incidence of sudden cardiac events, [meaning] people go into the ER for chest pain, arrhythmias, [and] heart attacks.”
A comprehensive study published in December 2022 in Circulation, which encompassed data from 27 countries, unearthed a strong association between exposure to extreme temperatures, whether hot or cold, and an elevated risk of death from cardiovascular causes, including stroke and heart failure.
“And there’s growing evidence that there’s an increased incidence of cardiac events on days of higher pollution,” Dr. Wold adds, ”like what was going on a couple of weeks ago with the Canadian air coming down.”
In addition, authors of another review on pollution and the heart, which was published November 2021 in The New England Journal of Medicine, noted that air pollution has been “causally linked to multiple risk factors for cardiovascular disease — most notably, hypertension and diabetes.”
“This new study is the most comprehensive and the first study I’ve seen that looks at the potential synergistic or combined effects of extreme temperature events and particulate matter exposure on death from heart attack,” says Dr. Wold.
The Adverse Impact of Wildfire Smoke and Air Pollution on Heart Health
To understand why this deadly association between extreme weather and heart attacks exists, it is vital to comprehend the detrimental effects of fine particulate pollution on the heart.
Particulate pollution, often referred to as PM or PM2.5, comprises solid and liquid particles suspended in the air. This pollution stems from various sources, with one of the most common being combustion-related events, such as wildfires.
During such incidents, the concentration of particulate matter in the air skyrockets to levels that can even be visible to the naked eye, as defined by the Environmental Protection Agency (EPA). Particles with a diameter of 10. Micrometers (µm) or smaller pose the greatest health risks because they can penetrate deep into the lungs and affect blood vessels around the heart. The tiniest particles, less than 2.5 microns in size, can reach even deeper into the lungs, potentially causing irritation and adverse cardiovascular effects.
Combining Heatwaves and High Pollution Could Double Heart Attack Risk in Elderly Individuals
To quantify the impact of extreme temperatures coupled with high levels of fine particulate pollution, researchers scrutinized more than 200,000 heart attack fatalities that occurred in Jiangsu province, China, between 2015 and 2020. This region experiences diverse seasons, a wide temperature range, and varying levels of fine particulate pollution.
The study population primarily consisted of older adults, with an average age of 77.6 years, and a substantial proportion of the deaths occurred in individuals over 80 years of age. It’s noteworthy that a majority of the fatalities were among men.
The researchers took into account particulate exposure on the day of each heart attack fatality and the day prior. Extreme temperatures were determined using the daily heat index, a measure that combines the effects of temperature and humidity. They also considered the duration and intensity of heatwaves and cold snaps.
Their analysis compared the days when heart attacks occurred (referred to as “case days”) with control days on the same day of the week in the same month. The presence of high particulate levels was determined when the average fine particulate matter concentration exceeded 37.5 micrograms per cubic meter, a threshold defined by the World Health Organization (WHO).
The results were striking. During two-day heatwaves with heat indices ranging from 82.6 to 97.9 degrees Fahrenheit, there was an 18 percent higher risk of heart attack death. This risk surged to a 74 percent increase during four-day heatwaves with heat indices between 94.8 to 109.4 degrees Fahrenheit. Most alarmingly, the risk of heart attack death doubled when the most scorching days coincided with high pollution levels.
Cooler Weather Imposes Lower Heart Risk Compared to Heatwaves
Cold days also carried an elevated risk, although it was not as pronounced. A two-day cold snap with temperatures ranging from 33.3 to 40.5 degrees Fahrenheit was associated with a 4 percent higher risk. This risk increased when temperatures dropped lower and persisted for longer durations.
For instance, a three-day cold snap with temperatures between 27.0 to 37.2 degrees Fahrenheit corresponded to a 12-percent higher risk of heart attack death. Interestingly, high levels of fine particulate pollution during cold snaps did not produce a similar increase in the risk of heart attack death.
The impact of these extreme weather conditions was not uniform across all demographic groups. Heatwaves were found to have a more pronounced impact on women compared to men. Additionally, individuals aged 80 and older faced a higher risk of heart attack death in all the studied conditions – heatwaves, cold snaps, or high pollution days.
Dr. Wold says, “I was not totally surprised that there was a synergistic effect between heat waves and high pollution. I was surprised that they did not find that cold exposure coupled with high particulate matter exposure caused a greater incidence of heart attack.”
The researchers estimated that up to 2.8 percent of heart attack deaths may be attributed to the combined influence of extreme temperatures and elevated fine particulate pollution levels.
“That 2.8 in percent increase in heart attack deaths seems like a really low number, but when you’re dealing with millions and millions of people, that is a very, very high number. And I anticipate that it’s actually on the low side of what truly is occurring,” he adds.
Reducing Heart Risk in Extreme Weather: Practical Steps to Follow
To mitigate the risks posed by extreme weather conditions, especially for women and older adults, study senior author Dr. Liu suggests a series of precautionary measures:
- Stay informed about weather forecasts, paying particular attention to the heat index and air quality measurements.
- Seek shelter indoors during extreme temperature conditions. If the air quality is acceptable, consider scheduling outdoor activities or exercise during cooler parts of the day. Wearing a mask when going outside can help reduce exposure to fine particulate pollution.
- Avoid busy highways when walking, and opt for less strenuous outdoor activities on days with high fine particulate pollution levels.
- Use fans and air conditioners during hot weather, and dress appropriately for the weather if outdoor exposure is necessary.
- Stay well-hydrated. Proper hydration is vital not only during exposure to extreme heat but also in the days leading up to and following such exposure.
Following recommendations from the University of Alabama-Birmingham, consuming 1 milliliter of fluids for every calorie consumed can help ensure adequate hydration. Simply put, if you consume 2,000 calories per day, you should drink at least 2,000 mL of fluids per day, equaling around 68 ounces. To better understand this amount, it’s advisable to speak with your health care provider.
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