Heat Wave and High Fine Particulate Pollution Days Double Risk of Fatal Heart Attacks

Research Highlights:

• An analysis of more than 202,000 heart attack deaths between 2015-2020 in a single Chinese province found that days that had extreme heat, extreme cold or high levels of fine particulate matter (PM_2.5) air pollution were significantly associated with the risk of death from a heart attack, especially in women and older adults.
• The greatest increase in the risk of death from heart attack was seen on days that had the combination of extreme heat and high levels of PM_2.5.
• The days with extreme heat were associated with an increased risk of heart attack death in women vs. men, and in older adults than in younger adults. Older adults were also at a greater risk of heart attacks compared to younger adults during days with extreme cold or high levels of PM_2.5.

Newswise — DALLAS, July 24, 2023 —A new study published in the American Heart Association’s journal Circulation suggests that the combination of intense heat and high levels of fine particulate pollution may significantly increase the risk of death from heart attacks. The study, which examined over 202,000 heart attack-related deaths in China, found that extreme temperature events are becoming more frequent and severe, raising concerns about their impact on public health.

The presence of fine particulate matter in the air is a global environmental issue, and when combined with extreme temperatures, it appears to have a synergistic effect on cardiovascular health. The study’s senior author, Dr. Yuewei Liu, an associate professor of epidemiology at Sun Yat-sen University in Guangzhou, China, highlighted the need to understand how these two factors interact and contribute to a higher risk of heart attack deaths. The acute nature of heart attacks and their significant disease burden worldwide make this a pressing public health challenge.

The researchers conducted a study to assess the impact of extreme temperatures in combination with high levels of fine particulate pollution on heart attack deaths. They analyzed data from 202,678 heart attack-related deaths that occurred in Jiangsu province between 2015 and 2020. Jiangsu has distinct seasons and experiences a wide range of temperatures and pollution levels. The study focused on older adults, with an average age of 77.6 years, where 52% were older than 80 years, and 52% were male. The researchers also considered particulate exposure on the day of each death and the day before.

To evaluate extreme temperatures, the researchers used the daily heat index, which takes into account both heat and humidity. They examined the duration and intensity of heatwaves and cold snaps. For analysis, they compared heart attack deaths during these periods, referred to as case days, with control days that were on the same day of the week in the same month. If a death occurred on a Wednesday, all other Wednesdays in the same month served as control days. High particulate levels were defined as days with an average fine particulate matter level above 37.5 micrograms per cubic meter.

The study’s senior author, Liu, emphasized that their findings provide evidence supporting the importance of reducing exposure to extreme temperatures and fine particulate pollution as a preventive measure against premature heart attack deaths, particularly among women and older adults.

In comparison to control days, the study revealed the following levels of increased risk for fatal heart attacks:

• During 2-day heat waves with heat indexes at or above the 90th percentile (ranging from 82.6 to 97.9 degrees Fahrenheit), the risk was 18% higher, and it further increased with temperature and duration. During 4-day heat waves with heat indexes at or above the 97.5th percentile (ranging from 94.8 to 109.4 degrees Fahrenheit), the risk was 74% higher. Approximately 3.2% (6,417) of the 202,678 observed heart attack deaths occurred during heat waves with heat indexes at or above the 95th percentile (ranging from 91.2 to 104.7 degrees Fahrenheit) for three or more days.
• During 2-day cold snaps with temperatures at or below the 10th percentile (ranging from 33.3 to 40.5 degrees Fahrenheit), the risk was 4% higher, and it increased with lower temperatures and duration. During 3-day cold snaps with temperatures at or below the 2.5th percentile (ranging from 27.0 to 37.2 degrees Fahrenheit), the risk was 12% higher. Approximately 3.1% (6,331) of the 202,678 observed heart attack deaths occurred during cold spells with temperatures at or below the 5th percentile (ranging from 30.0 to 38.5 degrees Fahrenheit) for three or more days.
• The risk was twice as high during 4-day heat waves that had fine particulate pollution levels above 37.5 micrograms per cubic meter. However, days with high fine particulate pollution levels during cold snaps did not show an equivalent increase in the risk of heart attack deaths.
• Overall, women experienced a higher risk of heart attack during heat waves compared to men.
• People aged 80 and older had a higher risk of heart attack during heat waves, cold snaps, or days with high levels of fine particulate pollution compared to younger adults.

The average age of all individuals who died from a heart attack in Jiangsu between 2015 and 2020, including during non-extreme temperature events, was 77.6 years old. Among them, 52.1% were over 80 years old.

 The researchers found that the combination of extreme temperatures and high levels of fine particulate pollution (> 37.5 micrograms per cubic meter), according to WHO targets, may be responsible for up to 2.8% of heart attack deaths.

To mitigate the negative health effects of extreme temperatures, Liu suggested several strategies for individuals, including monitoring weather forecasts, staying indoors during extreme temperatures, utilizing fans and air conditioners in hot weather, dressing appropriately for the weather, and maintaining proper hydration. Installing window blinds to reduce indoor temperatures can also be beneficial.

To minimize exposure to air pollution on days with high levels of fine particulate pollution, using air purifiers indoors, wearing masks while outdoors, avoiding busy highways when walking, and opting for less-strenuous outdoor activities are recommended.

In the interest of public health, Liu emphasized the importance of considering fine particulate pollution when issuing extreme temperature warnings to the public. By incorporating such measures, it is possible to improve public health outcomes and reduce the impact of extreme temperature and pollution on heart health.

The American Heart Association has issued both a scientific statement and a policy statement in 2020, providing comprehensive insights into air pollution exposure and outlining various individual, industrial, and policy measures to mitigate the detrimental effects of poor air quality on cardiovascular health. Reducing air pollution exposure and addressing its adverse impact on heart health, including heart disease and stroke, are crucial steps toward reducing health disparities in historically marginalized and under-resourced communities, particularly in Black and Hispanic populations and those with the highest levels of air pollution exposure.

The researchers emphasized the need for further investigation into the potential interactive effects of extreme weather events and fine particulate pollution on heart attack deaths in regions with varying temperature and pollution ranges to validate their findings. Notably, the study did not consider adjustments for adaptive behaviors adopted by individuals, such as using air conditioning and staying indoors during extreme temperatures or high pollution levels. This oversight may lead to misclassifying individuals’ exposure to weather conditions and could alter their risk patterns.

It is also essential to recognize that the study’s results may not be directly applicable to other regions in China or other countries due to potential differences in adaptive capacity and temperature distributions in various locations. This highlights the importance of considering regional variations and local contexts when applying the study’s findings to other areas.

Background:

Fine particulates, which are particles with a size of less than 2.5 microns, have the potential to be inhaled deep into the lungs, causing irritation to the lungs and blood vessels around the heart. They are commonly associated with fuel combustion, such as emissions from vehicles, factories, or wildfires. Previous research has established a clear link between exposure to particulate matter, including fine particulates, and various health issues, including heart disease, stroke, and other respiratory problems.

To provide context, the World Health Organization sets target levels for average annual exposure to fine particulate pollution, aiming for no more than 5 micrograms per cubic meter. Additionally, the target allows for no more than 15 micrograms per cubic meter on more than 3-4 days per year.

In the study, heat waves were defined based on the daily heat indexes (ranging from 82.6 to 109.4 degrees Fahrenheit) across Jiangsu province, China, and were categorized as periods at or above the 90th, 92.5th, 95th, and 97.5th percentiles, lasting for at least 2, 3, or 4 consecutive days.

On the other hand, cold spells were defined as periods at or below the 10th, 7.5th, 5th, and 2.5th percentiles of daily heat indexes (ranging from 27 to 40.5 degrees Fahrenheit), lasting for at least 2, 3, or 4 consecutive days.

Co-authors and authors’ disclosures are listed in the manuscript. This study was funded by China’s Ministry of Science and Technology.

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