Long-term exposure appears to increase the chances of developing these mental disorders, according to a large UK population-based study.
Long-term exposure to air pollution increases the risks of depression and anxiety, according to a major population-based UK cohort study.
Nearly 400,000 participants with no prior history of anxiety or depression were tracked for more than a decade to understand their level of exposure to common air pollutants such as nitrogen dioxide, nitric oxide and particulate matter.
Over the course of the study, more than 13,000 participants were diagnosed with depression and almost 16,000 were diagnosed with anxiety.
The authors found that people with the highest estimated exposure to multiple air pollutants were significantly more likely to develop one of these mental health conditions over the course of the study.
The quarter of participants with the highest exposure to these pollutants were 16% more likely to develop depression and 11% more likely to develop anxiety than the quarter with the lowest exposure.
While previous studies have studied the link between short-term exposure and hospitalisations or healthcare visits, few studies have investigated the long-term consequences of air pollution on mental health.
This study found that the risks rose most steeply in the lower exposure groups, but plateaued at higher exposures.
“Increased associated risk for both depression and anxiety was observed even at concentration levels below the annual values in UK air quality standards,” the authors wrote in JAMA Psychiatry.
“Thus, the findings suggest that stricter standards or regulations for air pollution control are essential, and reductions in exposure to multiple air pollutants may alleviate the disease burden of depression and anxiety.”
The mechanisms which contribute to this association are not fully understood, but researchers posited that olfactory receptor neurons exposed to air pollution may trigger a central nervous system response. Systemic circulation and the trigeminal nerve may also contribute to the inflammatory and oxidative stress response, and air particulates may induce the release of proinflammatory mediators, activate the hypothalamic pituitary adrenal axis and damage the blood-brain barrier.
One strength of the study was that researchers were able to adjust for household income to control for socioeconomic status, as well as confounders such as age, sex and other demographic factors.
Annual mean air pollution was estimated using concentration of air particulates, nitric oxide and nitrogen dioxide at participants’ residential addresses. Particulate matter was separated into two groups – PM2.5 were particulates with an aerodynamic diameter of 2.5?m or less, and PM2.5-10 had an aerodynamic diameter of 2.5-10 micrometres.
Researchers described the current global ambient air pollution as an urgent public health priority and a major worldwide health issue.
“The non-linear association may have important implications for policy making in air pollution control,” they wrote. “Reductions in joint exposure to multiple air pollutants may alleviate the disease burden of depression and anxiety”.
