Air pollution is the fourth-largest threat to human health, behind high blood pressure, dietary risks and smoking, and it has been linked to mental distress as well.
A study from the University of Washington published in November 2017 found a higher rate of mental distress in high-pollution areas.
The study is the first of its kind to utilize data from the United States to assess the relationship between exposure to air pollution and reports of psychological distress.
"Our study finds that the brain, not just the heart and lungs, may be negatively impacted by exposure to air pollution," said Victoria Sass Ph.D. Student Interface Demography at the University of Washington.
The study suggests that public health efforts to reduce the personal and societal costs of mental illness should consider addressing not only individual characteristics and factors in the social environment, but also facets of the physical environment such as air pollution.
"Our study finds evidence that exposure to higher levels of fine particulate matter is associated with higher levels of psychological distress," Sass said.
Sass thinks the main finding is extremely compelling and warrants further research.
"The literature on the effects of air pollution for respiratory and cardiovascular diseases is pretty well-documented but not a lot has been done on the effects of air pollution directly on the brain," Sass said.
During the research they looked at pollution levels between 1999 and 2011, as well as a population sample’s self-reported “psychological stress” which included their feelings of hopelessness, sadness or nervousness.
Sass and her colleagues found that psychological distress scores in high-pollution areas were 17 percent higher, even after controlling for several behavioral, socioeconomic and health factors.
Sass said understanding the mechanisms by which air pollution impacts psychological distress was beyond the scope of this study, but it does warrant further research.
"It is important to note that the associations we found were not the same for all groups (or pollutants) and thus there is a need for a fuller examination into the direct and indirect ways through which air pollution acts on mental health," Sass said.
The air pollution measured is called “fine particulate matter” which are incredibly tiny chemical particles. If there are enough particles, they can cast a haze over areas experiencing a high output.
Less than 2.5 micrometers in diameter, a single particle of this air pollution is about 1/28 the width of a single strand of hair.
"It may be common to think that clean air and water are a given in the United States, but I think it is becoming clearer that that simply is not the case," Sass said.
This type of pollution that they examined primarily comes from cars, coal or natural gas power plants, factories, construction sites, fires and other sources.
"While the modal trend over the last three decades has been decreasing levels of air pollution due to requirements set by the Clean Air Act and enforced by the EPA, those levels can rise without rigorous enforcement and ongoing research that informs appropriate healthy standards," Sass said.
"Given that air pollution is easily modifiable through policies at every level of government, these negative health outcomes are ones that can be avoided with the political will to make individual and population health a priority," Sass said.