Excess heart attack mortality occurs during heat waves, days of poor air quality in China

ByScott Buzby

Fact checked byRichard Smith

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Key takeaways:

Nearly 3% of all heart attack deaths during a 5-year period in China could be attributed to extreme temperature exposure and poor air quality.
The odds of MI death during heat wave exposure increased up to 74%.

Researchers in China estimated that nearly 3% of all MI deaths in Jiangsu province during a 5-year period could be attributed to a combination of extreme temperature exposure and poor air quality.

The time-stratified case-crossover study published in Circulation included 202,678 MI deaths from 2015 to 2020. Researchers evaluated the association between exposure to heat waves, cold spells and fine particulate matter (PM_2.5) with MI death.

Air pollution in China — Nearly 3% of all heart attack deaths during a 5-year period in China could be attributed to extreme temperature exposure and poor air quality.
*Image: Adobe Stock*

“Extreme temperature events are becoming more frequent, longer and more intense, and their adverse health effects have drawn growing concern. Another environmental issue worldwide is the presence of fine particulate matter in the air, which may interact synergistically with extreme temperatures to adversely affect cardiovascular health,” Yuewei Liu, MD, PhD, associate professor of epidemiology in the School of Public Health at Sun Yat-sen University in Guangzhou, China, said in a press release. “However, it remains unknown if and how co-exposure to extreme temperatures and fine particulate pollution might interact to trigger a greater risk of death from heart attack, which is an acute response potentially brought on by an acute scenario and a great public health challenge due to its substantial disease burden worldwide.”

Linking mortality and meteorological datasets

For this study, Liu and colleagues linked mortality data from the Jiangsu provincial mortality surveillance system to daily meteorological data from the China Meteorological Administration Land Data Assimilation System and daily ambient air pollution data from the ChinaHighAirPollutants dataset. Community-level climate and pollution data were compared with timing of MI mortality.

Most of Jiangsu has a humid subtropical climate with four distinct seasons, whereas the climate in the northernmost areas transitions to a humid continental climate, the researchers wrote.

The researchers defined heat wave as daily temperature equal to or higher than the 95th percentile of temperature for at least 3 consecutive days and cold spell as daily temperature lower than or equal to the 5th percentile of temperature for at least 3 consecutive days.

Extreme temperature, PM_2.5 and MI death

Liu and colleagues estimated that up to 2.8% of the MI deaths from 2015 to 2020 were attributable to extreme temperature exposure and PM_2.5 at levels exceeding WHO air quality guidelines (37.5 g/m³).

The OR for MI death associated with a heat wave ranged from 1.18 (95% CI, 1.14-1.21) to 1.74 (95% CI, 1.66-1.83) and the OR for MI death associated with a cold spell ranged from 1.04 (95% CI, 1.02-1.06) to 1.12 (95% CI, 1.07-1.18).

After adjustment for extreme temperature exposure, the likelihood of MI death increased monotonically with increasing PM_2.5 exposure and attenuated after an estimated breakpoint of 39.5 g/m³ (P for nonlinearity < .05), according to the study.

The researchers observed a synergistic effect between exposure to heat waves and PM_2.5 and increased odds for MI death; however, no interactive effect was observed between cold spell exposure and PM_2.5 and odds for MI death.

“Strategies for individuals to avoid negative health effects from extreme temperatures include following weather forecasts, staying inside when temperatures are extreme, using fans and air conditioners during hot weather, dressing appropriately for the weather, proper hydration and installing window blinds to reduce indoor temperatures,” Liu said in the release. “Using an air purifier in the house, wearing a mask outdoors, staying clear of busy highways when walking and choosing less-strenuous outdoor activities may also help to reduce exposure to air pollution on days with high levels of fine particulate pollution. To improve public health, it is important to take fine particulate pollution into consideration when providing extreme temperature warnings to the public.”