A study has revealed the dual threat posed by air pollution – depression and stress along with cardiovascular disease linked to poor mental health.

Researchers looked at data from more than 3,000 counties in the U.S., encompassing around 315 million residents. Their findings linked air pollution with stress and depression, which puts middle-aged adults at a greater risk of dying from heart disease.

Study lead author Dr Shady Abohashem, from Harvard Medical School, said: “Our study indicates that the air we breathe affects our mental well-being, which in turn impacts heart health.

“Our results reveal a dual threat from air pollution: it not only worsens mental health but also significantly amplifies the risk of heart-related deaths associated with poor mental health.

“Public health strategies are urgently needed to address both air quality and mental wellbeing in order to preserve cardiovascular health.”

The research concentrated on fine particles (PM2.5), which are less than 2.5 micrometres in diameter. These particles, which pose the greatest risk to health, are found in vehicle exhaust fumes, power plant combustion and burning wood.

Exposure to PM2.5 was measured as high or low based on World Health Organization (WHO) standards. The research team also collected data on the extent to which residents experienced mental health problems.

Counties were then categorised into three groups according to the results.

Researchers found that counties with higher levels of fine particles were 10% more likely to report more days of poor mental health, compared to counties with lower levels of fine particles.

This risk was seen most significantly in counties with higher numbers of minority groups, or poverty.

Furthermore, a strong link was seen between poor mental health and early death from cardiovascular disease in counties with high levels of air pollution.

Poor mental health was linked to a three-fold increase in early death from cardiovascular disease in these counties. Researchers found that a third of these pollution-linked cardiovascular deaths were attributed to the burden of poor mental health.

The World Health Organization estimates that air pollution was responsible for around 4.2 million early deaths globally in 2019.

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