Heat and pollution: a deadly combination that triggers the risk of heart attack

Although there are various factors that can double the risk of heart attack, there is a combination that is especially deadly: heat and high levels of pollution by fine particles, two elements that trigger the risk of death, especially in the elderly and women.

This is the main conclusion of a study published this Monday in Circulation – the journal of the American Heart Association – based on the analysis of more than 202,000 deaths from myocardial infarction between 2015-2020 in the Chinese province of Jiangsu, a region with four distinct seasons and a wide range of temperatures and levels of pollution by fine particles.

Fine particles less than 2.5 microns in size come from car exhaust, factories or fires, and inhalation causes heart disease and stroke among other problems.

These particles “can interact synergistically with temperature extremes and adversely affect cardiovascular health,” said lead author Yuewei Liu, a researcher at Sun Yat-sen University's School of Public Health in Guangzhou, China.

To find out if joint exposure to extreme temperatures and pollution affects health, the team analyzed 202,678 heart attack deaths between 2015-2020 recorded in Jiangsu.. The study confirmed that the days that combined extreme heat and high levels of air pollution by fine particles increased the risk of death by heart attack, more in women than in men and in older adults more than in young people.

Specifically, the deaths occurred among adults with a mean age of 77.6 years, 52% were over 80 years of age and 52% were men.

Temperature extremes were measured based on an area's daily heat index that includes the combined effect of heat and humidity.. And both the duration and intensity of heat waves and cold waves were assessed.

Myocardial infarction deaths, or 'case-days', during these periods were compared to control dates on the same weekday of the same month, i.e. if a death occurred on a Wednesday, all other Wednesdays of the same month would be considered control days.

Increased risk of fatal heart attack in heat waves lasting several days

Particle levels were considered high on any day with a mean level of fine particles greater than 37.5 micrograms per cubic meter. Compared with control days, the risk of fatal heart attack increased by 18% in 2-day heat waves with heat indices at or above the 90th percentile (28.1 to 36.6 degrees Celsius), and up to 74% more in 4-day heat waves with heat indices at or above the 97.5th percentile (34.8 to 43 degrees C).

Cold-related infarcts were 4% more frequent during 2-day cold waves with temperatures at or below the 10th percentile (between 0.7 and 4.7 degrees Celsius), and 12% more frequent during 3-day cold waves with temperatures at or below the 2.5th percentile (between -2.7 and 2.7 degrees Celsius).

However, with contamination greater than 37.5 micrograms per cubic meter, deaths increased in 4-day heat waves but not in cold ones.

By sex and age, more deaths were detected among women than among men during heat waves and among people aged 80 and over. The median age of all individuals who died of a heart attack in Jiangsu between 2015 and 2020, even during non-extreme temperature events, was 77.6 years; 52.1% of these individuals were over 80 years of age.

“Our findings demonstrate that reducing exposure to both extreme temperatures and fine particle pollution may be helpful in preventing premature death from heart attack, especially for women and older adults,” Liu said.