Breathing polluted air can make you depressed, study finds

Air pollution affects the physical health of millions of people around the world. It could also play a major role in the increase in mental disorders, particularly depression, according to this new study.

The study recently published in the journal Environmental Science and Ecotechnology confirms a worrying link. Indeed, prolonged exposure to air pollution would be directly linked to the risk of develop depressive symptoms. These results appear in a context where pollution levels continue to be well above the thresholds recommended by the World Health Organization (WHO).

A step forward in understanding the effects of air pollution

The research was carried out by theHarbin Medical University and Cranfield University. For the study, scientists analyzed data from more than 12 000 participants of the investigation China Health and Retirement Longitudinal Study (Charles).

This is how they were able to identify several air pollutants. They demonstrated a correlation between breathing sulfur dioxide (SO₂), fine particles (PM2.5) and carbon monoxide (CO) and a significant risk of developing depression.

The most dangerous pollutants in the air: SO₂, PM2.5 and CO

The new study has the merit of providing a ranking of the most dangerous pollutants contained in the air.

1 – Sulfur dioxide (SO₂)

Among the pollutants studied, sulfur dioxide (SO₂) appeared to be the most significant in the development of depressive symptoms. Note that SO₂ is a gas present in the air mainly due to industry, vehicles and the burning of fossil fuels. Therefore, its presence in the atmosphere is of particular concern in urban and industrial areas.

2 – Fine particles (PM2.5)

Fine particulate matter (PM2.5), which are tiny particles suspended in the air, have also been identified as risk factors. These particles come from various sources such as car traffic, industries, power plants and even forest fires. They penetrate deep into the lungs and can travel to the bloodstream, affecting vital organs and potentially the brain.

3 – Carbon monoxide (CO)

Finally, carbon monoxide (CO) is an odorless and invisible gas. It is mainly generated by incomplete combustion of fuels. And it would also be linked to a high risk of depressive symptoms. Although less publicized than other pollutants, CO in fact plays an underestimated role in mental disorders, particularly in urban environments.

The study also reveals that the impact of pollutants on mental health is amplified when several types of pollution are present simultaneously. Concretely, the researchers discovered that together, these pollutants affect not only physical but also cognitive functions. Thus, prolonged exposure to these agents could lead to alterations in certain regions of the brain, particularly those that regulate emotions.

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An impact on the emotional development of children

Recent research has also shown that long-term exposure to fine particles (PM2.5) and nitrogen dioxide (NO2) could affect the emotional and behavioral development of young people.

Indeed, we now know that children living in heavily polluted areas are more likely to present symptoms of anxiety, depression and aggressive behavior. In addition, they would be more vulnerable to attention disorders, such as ADHD (attention deficit disorder with or without hyperactivity). The fact is that young brains, still developing, seem particularly sensitive to environmental influences.

How can we explain the biological mechanisms behind this link?

The biological mechanisms explaining the link between air pollution and depression are still being studied. However, several hypotheses have been put forward. One of the major explanations lies in systemic inflammation. Indeed, exposure to air pollution induces inflammation which can affect the brain. This inflammation can notably alter brain structures involved in the regulation of emotions, such as the amygdala and the prefrontal cortex.

Fine particles, in particular, can enter the blood system and reach the brain, where they can cause chronic inflammation. This inflammation can damage neural circuitsthus affecting cognitive and emotional processes. Furthermore, we know that air pollution could disrupt the levels of neurotransmitters, such as serotonin. However, we know that the latter play a key role in regulation of mood and mental well-being.

Cognitive degradation progressive due to air pollution

The effects of air pollution are not limited to the impact on immediate mental health. Indeed, prolonged exposure to high levels of pollution may contribute to cognitive decline and neurodegenerative conditions. In the list there is Alzheimer's disease and Parkinson's disease.

These diseases, which mainly affect the elderly, are increasingly linked to environmental factors. In fact, exposure to pollutants in the air could accelerate the deterioration of brain functions.

What implications for public health and environmental policies?

The results of this study highlight the importance of concerted action to reduce air pollution. Air pollution undeniably represents a major threat to public health. And its impact on depression could result in considerable long-term social and economic costs.

Researchers are therefore calling for stricter air quality management policies. Also, measures such as promoting clean energy, strengthening vehicle emission standards and improving energy efficiency in industrial sectors could thus mitigate these harmful effects on mental health.