Discovering a dual health effect of air pollution on middle-aged adults

A recent study found that air pollution is linked to stress and depression, putting middle-aged adults at increased risk of death from cardiovascular disease.

The study, the results of which were presented at the Preventive Cardiology 2024 Conference of the European Society of Cardiology (ESC), was conducted in more than 3,000 American counties, with a population of 315 million people.

“Our study suggests that the air we breathe affects our mental health, which in turn affects heart health,” said the study’s lead author, Dr. Shadi Abu Hashem, from Harvard Medical School in Boston, US.

According to the World Health Organization, air pollution is estimated to have caused 4.2 million premature deaths worldwide in 2019. Mental illnesses have also been linked to premature death. This study examined whether air pollution and poor mental health are interconnected and have a joint effect on death from cardiovascular disease.

The study focused on particles less than 2.5 micrometers in diameter, also referred to as fine particulate matter or PM2.5. They come from automobile exhaust fumes, power plant combustion, and wood burning, and represent the highest health risks.

To conduct the study, county-level data on annual PM2.5 levels were obtained from the Centers for Disease Control and Prevention (CDC). Exposure to PM2.5 particles was classified as high or low according to World Health Organization standards.

The researchers collected data on the average number of days county residents experienced mental health problems, including stress, depression and emotional problems, from the CDC. Each county was then classified into three groups based on these numbers.

The team also obtained age-adjusted (under 65 years) premature cardiovascular disease death rates for each county from the CDC.

The study included 3,047 US counties, containing more than 315 million residents (with more than 207 million residents aged 20 to 64 years and 50% female) in 2013.

Between 2013 and 2019, about 1,079,656 (0.34%) of participants died from cardiovascular disease before the age of 65 years.

The researchers analyzed the associations between pollution, mental health, and premature cardiovascular disease mortality after adjusting for factors that could influence the relationships.

Counties with polluted air (high PM2.5 concentrations) were 10% more likely to report high levels of “poor mental health” (PMH) days than counties with clean air (low PM2.5 concentrations).

This risk was significantly greater in counties with high rates of minority prevalence or poverty. The association between “poor mental health” and premature deaths from cardiovascular disease was stronger in counties with higher levels (above WHO recommended levels: greater than or equal to 10 micrometres) of air pollution. In these counties, higher levels of “poor mental health” (PMH) were associated with a three-fold increase in premature deaths from cardiovascular disease compared with lower levels of “poor mental health.”

Dr Abu Hashem said: “Our findings reveal a dual threat from air pollution: not only does it worsen mental health, it also exacerbates the risk of heart-related deaths associated with poor mental health. Public health strategies to address both air quality And mental health in order to maintain cardiovascular health.”