There may be a link between particulate air pollution and anxiety, warn researchers from the Johns Hopkins University in Baltimore.
Postdoctoral fellow Melinda C. Power, Ph.D., and her colleagues explain that anxiety disorders are characterized by disruptive fear, worry, and related behavioral problems such as avoidance. About 16 percent of the population will be diagnosed with an anxiety disorder in their lifetime, and the condition is linked to a raised risk of suicide.
“Remission is not always possible,” they state in the British Medical Journal. So “it is imperative to identify modifiable risk factors for anxiety disorders and symptoms.”
One possible environmental exposure that may be related to anxiety is air pollution, specifically exposure to fine particulate matter air pollution. This “may induce or exacerbate anxiety through increased oxidative stress and systemic inflammation or through promotion or aggravation of chronic disease,” say the experts.
The team examined this potential link using figures from 71,271 women aged 57 to 85 years taking part in a long term U.S. study called the Nurses’ Health Study. All filled in the Crown-Crisp Experiential Index (CCEI) of anxiety (previously known as the Middlesex Hospital Questionnaire).
It included eight questions on symptoms including fearfulness, desire for avoidance, and tendency to worry. Factors including socioeconomic status, education, age, and marital status were also taken into account.
About 15 percent of the women had high anxiety symptoms, that is, a score of six or more points on the phobic anxiety subscale of the CCEI.
Their exposure to particulate air pollution was measured in the one month, three months, six months, one year, and 15 years prior to assessment of anxiety symptoms, and residential distance to the nearest major road two years prior to assessment.
High anxiety symptoms were significantly linked with higher exposure to particulate air pollution at both one month and 12 months before anxiety was measured. Living nearer a major road was not related to anxiety symptoms.
They conclude that further research is warranted on the effect of reductions in exposure to particulate air pollution on anxiety.
“The most biologically relevant period of exposure is currently unknown,” writes the team. They point out that if particulate matter triggers anxiety via chronic oxidative stress, inflammation, or induction of chronic disease, then long-term exposure is most likely to blame.
But if it causes anxiety by aggravating chronic disease or short-term changes in oxidative stress or inflammation, then exposure closer to assessment of anxiety will be more relevant.
In this study, the link between fine particulate matter and anxiety appeared to be primarily driven by shorter-term exposure.
One potential limitation of the study is that the participants were relatively old, so the authors warn, “It is possible that our results would not generalize to younger age groups.”
Having said that, the findings are consistent with two previous studies of other air pollutants and anxiety, as well as research suggesting links between air pollution and other mental health outcomes including depression, acute psychiatric incidents, and suicide.
In a linked editorial, Professor Michael Brauer of the University of British Columbia in Canada, states that this study confirms “the urgent need to manage air pollution globally as a cause of ill health.”
He adds that reducing air pollution could be a cost-effective way to reduce the large burden of disease from both stroke and poor mental health.
“The effects of air pollution on the lungs and heart are now widely appreciated, with expanding evidence for an important role in cardiac disease,” he writes.
“The Global Burden of Disease Study identified fine particulate matter (PM2.5) in outdoor air and household air pollution from use of solid fuels as the ninth and fourth leading risk factors, respectively, for disease worldwide, and the World Health Organization attributes one in every eight deaths to air pollution.”
“Further, an important point in the context of air pollution, is that even small relative risks may translate into large population attributable risks given the near-ubiquitous exposure to air pollution,” Brauer writes.
“This contrasts with other factors which may have much larger relative risks for stroke, for example cocaine use, but for which there is much lower exposure prevalence leading to a lower population attributable risk in comparison with air pollution.”
Power, M. C. et al. The relation between exposure to fine particulate air pollution and anxiety: a cohort study. BMJ 2015;350:h1111
Brauer, M. Air pollution, stroke, and anxiety. BMJ 2015;350:h1510