Smog getting you down? New study shows PM2.5’s impact on human stress levels

PM2.5 is often associated with respiratory diseases, cardiovascular risks, and premature mortality. However, the full nature and extent of what happens when these particles enter our system is still being explored. A group of researchers based in Shanghai recently published a study unveiling some lesser-known impacts of PM2.5 on the human body.1

Dr. Haidong Kan, along with ten colleagues of Fudan University, Shanghai, decided to dig deeper into the effects of PM2.5 on healthy adults. According to the researchers, PM2.5 is known for adverse health effects, but “potential mechanisms are largely unknown”. Dr. Haidong Kan mentions that it is “increasingly necessary for people to understand the importance of reducing their PM exposure”. Among the study’s findings, a notable discovery is that exposure to higher levels of PM appears to trigger a spike in stress hormones.

To carefully analyze the effects of PM2.5 on the level of metabolism, two tests were conducted for nine days. Fifty-five healthy college students in Shanghai were randomly selected and assigned to stay at their dormitory as much as possible, aside from classes, inside which were placed either working or non-working (sham) air purifiers. Then, after a 12-day intermission, the working and non-working air purifiers were swapped. At the end of both nine-day periods, tests were made using the students’ blood and urine to observe their contained level of certain molecules. During the test time, the students stayed in non-smoking dormitories and were asked to refrain from cooking or cleaning to reduce the risk of additional external sources of PM2.5.

An typical college dormitory. Photo courtesy of

Overall, the functional air purifiers reduced the average PM2.5 exposure of the students by half, from 53.1 μg/m3 to 24.3 μg/m3. As Dr. Robert D. Brook of the University of Michigan observes, “Simple actions taken at a personal level, including usage of air purifiers with HEPA filters, can substantively reduce exposures and help lessen the harmful health effects of (PM).”2 From wearing protective respiratory masks to using air purifiers, reducing exposure can “actually reduce hard cardiovascular events and mortality among high risk patients living in heavily polluted countries."

Smog in Beijing. Photo courtesy of Business Insider.

The first of its kind, the study reveals the direct influence of PM2.5 on the human body’s central nervous system, impacting hormone levels and metabolic mechanisms.

The results of the tests on the students showed that PM2.5 interacted with many hormones and metabolic mechanisms. Exposure to PM2.5 significantly increased levels of stress hormones, like cortisol, cortisone, epinephrine, and norepinephrine. Higher blood pressure, inflammation, and insulin resistance were also observed for the students exposed to higher levels of PM2.5. Interestingly, these high levels of stress hormones were reduced in the short-term after indoor air purification – thereby demonstrating the necessity of using an air purifier to clean indoor air.

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