A new study links levels of air pollution with episodes of high anxiety in women.
Researchers from Harvard and Johns Hopkins reported in March that they have shown a clear and significant association between levels of fine particulate matter in the air with episodes of high anxiety. This is anything but good news.
The researchers led by Melinda Power of the Harvard School of Public Health conducted an observational cohort study to determine whether higher past exposure to particulate air pollution could be associated with high symptoms of anxiety.
They looked to the Nurses Health Study (NHS) for data. The NHS is a prospective cohort study of women started in 1976 with a total of 121,701 nurses originally enrolled. From this massive group 71,271 women were selected who lived in the contiguous United States and for whom valid data for particulate matter exposure were available during the time periods of interest. Ages of the women ranged between 57 and 85 years (mean of 70 years).
The researchers compared two things, exposure to particulate matter in the air where these women lived with the results of an anxiety survey. To determine particulate exposure, the researchers used the women’s home addresses, which are updated every two years as part of the study, and using latitude and longitude data estimated particulate air pollution exposure (PM); this exposure was characterized by standard size categories (PM2.5 or PM2.5-10) during the one-month, three-months, six-months, one year and 15 year time periods prior to an assessment for anxiety symptoms. Distance of residence from major roads two years prior to anxiety assessment was also determined. Anxiety levels were assessed using the Crown-Crisp phobic anxiety scale as part of the NHS protocol.
Being exposed to higher levels of the small, PM2.5, particulate matter increased the odds a woman would have high anxiety symptoms when tested.
For example, for every per 10 µg/m(3) increase in the prior one month average of PM2.5 exposure a study participant’s odds of having high level anxiety increased by 12%. This same size increase in exposure to PM2.5 during the prior 12 months increased odds of high anxiety by 15%. Thus it seems that short-term exposure, in the month before, appeared more relevant than long-term exposure. Neither the larger particulate sizes (PM2.5-10), nor living close to major roads, seemed to be associated with anxiety, at least in this study. 
The results of this study caught me by surprise. To this point we have associated high levels of particulate matter mainly with cardiovascular (CVD) and respiratory diseases not with mood disorders.
Particulate matter is well associated with negative health effects. In an article
Walter Crinnion ND is writing for an upcoming special issue of NMJ on environmental medicine, he writes that particulate matter,
“… causes significant oxidative damage in the tissues and organs that they are distributed to [2-4] and have been associated with increased mortality primarily from cardiovascular [5,6], respiratory  and neoplastic diseases  . PM of all size act as a carrier for a number of other potent air pollutant chemicals including polycyclic aromatic hydrocarbons and volatile organic compounds, which may account for some of their toxic health effects  .”
The idea that PM pollutants might also impact mood is still relatively new. The majority of such papers have focused on depressive symptoms. In a 2012 paper on women in rural India, Bannerjee et al reported a strong correlation between cooking on biomass with depression. (Biomass is a euphemism for animal fecal material I think) The explanation offered to explain this association was the high PM levels in their homes, the result of their cooking method .
A 2014 paper Cho reported a significant association between air pollutant levels in Korea with the number of emergency room visits for depressive complaints .
In a January 2105 review, Tzvian et al reported on 15 articles identified related to the long-term effects of air pollution and also 8 on ambient noise levels. “Both exposures were separately shown to be associated with one or several measures of global cognitive function, verbal and nonverbal learning and memory, activities of daily living, depressive symptoms, elevated anxiety, and nuisance.” Unfortunately no study examined both exposures at the same time and it is often hard to separate the two factors. For example, an April 2015 study tells us that traffic wardens in Pakistan have above average levels of depression, stress, public conflict, irritation, behavioral affects, speech interference, hypertension, loss of concentration, hearing impairment, headache and CVD. The authors of this study blamed high noise levels for these cognitive effects though they did not report particulate matter exposure levels. One would suspect such exposure was high.
A March 2014 study that sought an association between particulate matter levels and depression in Boston was unable to prove one . This paper was immediately criticized for methodology .
The small airborne particles (PM2.5 or smaller) that were associated with increased anxiety in this paper by Power et al, are small enough to cross from lungs to blood and then across the blood brain barrier to reach the brain. This is probably why air pollution is associated with stroke and depression in adults and why children
“…. show significant systemic inflammation, immunodysregulation at systemic, intratechal and brain levels, neuroinflammation and brain oxidative stress, along with the main hallmarks of Alzheimer and Parkinson’s diseases…..”[`5].
This current report of a significant association with PM and anxiety should not come as a surprise. The only surprise is that we hadn’t considered this possibility until now. These results certainly have a clear clinical implication. We should consider the potential impact of air quality on any patient with anxiety symptoms.
Potential improvement in anxiety symptoms might be achieved simply by using an air filter at home. Few medical interventions will come with a lower risk profile than this, a consideration often important for anxious patients. The potential side effects of using an air filter are all desirable, particularly reduced CVD risk and according to a March 2015 paper, reduced risk of stroke .
This is one of those things that fit clearly under the heading, “might help; won’t hurt, worth a try.”
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