I often find that natural spaces and fresh air have a calming, balancing effect, and judging by the cultural association between relaxation and the outdoors, I'm not alone. Now some new research backs up the connection. Yesterday, the British Medical Journal published an article linking air pollution with anxiety, as well as an editorial on air pollution's health effects and another study elaborating on a previously-noted connection between pollution and stroke.
The anxiety study, conducted by researchers at Harvard and Johns Hopkins University, showed a significant connection between exposure to fine particulate pollution and symptoms of anxiety for more than 70,000 older women (mean age of 70 years) in the contiguous United States. Bigger particles appeared to have no effects, interestingly, nor did living close to a major road. The connection was present over a variety of time periods from one month to fifteen years, but was stronger in the short term. This evidence shows a clear need for studies to be done in other demographic groups, and to elaborate on the biological plausibility of the connection.
The stroke article, meanwhile, is a meta-analysis of 103 studies conducted in 28 countries and including 6.2 million events. Researchers found that both gaseous and particulate air pollution had a "marked and close temporal association" with strokes resulting in hospital admissions or death.
As stated in the editorial, particulate air pollution has already been shown to be a contributing factor in a variety of serious health conditions, including a well-supported link to cardiopulmonary diseases, but also diabetes, low birth weight, and pre-term birth. In fact, the World Health Organization estimates that one of every eight deaths is caused by air pollution. The body of research on the topic suggests that pollution may initiate systemic inflammation, thereby affecting multiple organ systems.
With such a broad range of detrimental effects, and because it affects such a significant percentage of the population, air pollution is becoming a top public health concern. As the University of British Columbia's Michael Brauer, ScD, wrote in the editorial:
The findings of these two studies support a sharper focus on air pollution as a leading global health concern... One of the unique features of air pollution as a risk factor for disease is that exposure to air pollution is almost universal. While this is a primary reason for the large disease burden attributable to outdoor air pollution, it also follows that even modest reductions in pollution could have widespread benefits throughout populations. The two linked papers in this issue confirm the urgent need to manage air pollution globally as a cause of ill health and offer the promise that reducing pollution could be a cost effective way to reduce the large burden of disease from both stroke and poor mental health.