Air Pollution Linked to Increased Risk of Anxiety
Following a somewhat unconventional line of thought, the Johns Hopkins/Harvard researchers were curious to find out if exposure to physical irritants might foster or exacerbate anxiety. And sure enough, the data they uncovered provided evidence affirming their intuition.
Anxiety Is in the Air
To complete their analysis, the research team used information acquired from the database of the ongoing U.S. Nurses’ Health Study. Statisticians working on this decades-old project have collected detailed data on the lives and medical histories of tens of thousands of practicing nurses, providing medical researchers with a treasure trove of data relating to women’s health.
For the purposes of the Johns Hopkins/Harvard project, 70,000 women between the ages of 57 and 85 were selected for further health review. Following evaluation for anxiety, they were graded on a continuum in order to facilitate the search for links between air pollution exposure and an increased incidence of anxiety disorder.
After mapping home addresses for study subjects, the researchers were able to measure likely exposure to air pollution by calculating their residential proximity to heavily traveled roadways and known industrial emitters, with adjustments made for climate and geography. To make their comparisons even more precise, they divided their subjects into smaller groups based on age, marital status, education level and socioeconomic or class status. The scientists correlating the data used intervals of 15 years, one year, six months, three months and one month to measure cumulative exposure within defined time periods.
Among women with varying levels of exposure to air pollution, differences in the manifestation of anxiety were not detectable over longer periods of time. Women with limited exposure were just as likely to test positive for debilitating anxiety over a 15-year period, or even a one-year period, as women with high exposure.
But when the time period measured was just a month, the picture changed. Using this interval for comparison, women with the greatest exposure to one particular type of air pollution (fine particulate, meaning particles 2.5 micrometers or smaller) were 12 percent more likely to experience symptoms consistent with an anxiety disorder than those with the least exposure. Large particulate exposure was not a predictor for anxiety over any length of time, but freshly inhaled fine particulates did appear to create a statistically significant increase in the incidence of high anxiety.
A Solution in the Pollution?
The counterintuitive nature of this finding—what could air pollution possibly have to do with anxiety, anyway?—has not been lost on the Johns Hopkins/Harvard research team. They freely admit there could be other anxiety-causing factors at work that might be common in the lives of people who live in close proximity to pollution sources.
The researchers did make adjustments for some demographic characteristics—like poverty, for example—that might have tended to skew study results (presumably those living close to factories, major highways or large agricultural operations would choose to reside elsewhere if they could afford it, and their life situations are likely anxiety-inducing in general). But there could be other factors at work that are more difficult to quantify, such as high levels of noise pollution, for example, which is more common near highways and factories and might be stimulating people’s nervous systems in subtle but important ways.
The researchers have suggested inflammation in the body might cause a chain reaction of troubling effects that could lead to greater levels of anxiety (inflammation is caused by exposure to toxins). Inflammation is known to cause a number of physical ailments, and mind-body factors could cause those effects to resonate through the nervous system. But connecting inflammation to anxiety is strictly theoretical at this stage and can only be viewed as one possibility.
Air pollution may or may not be a real cause of anxiety disorders. But whether it is or isn’t, the continuing search for answers this new study will spur should help mental health experts gain a greater understanding of conditions that adversely affect the lives of tens of millions of Americans.