SHANGHAI, CHINA — Healthy Chinese college students experienced a range of adverse cardiometabolic responses after short-term indoor exposure to high levels of particulate matter (PM) in a small, randomized crossover study[1].
Although levels of outdoor air pollution remained very high throughout, after just 9 days of breathing filtered room air with half the usual levels of small particles, the students had lower levels of stress hormones, blood pressure, and biomarkers of inflammation and oxidative stress, Huichi Li (Fudan University, Shanghai, China) and colleagues report in their article published in the August 15, 2017 issue of Circulation.
The findings suggest that air pollution causes “activations of the hypothalamus-pituitary-adrenal and sympathetic-adrenal-medullary axes [that] may contribute to the cardiovascular metabolic risks,” senior author Dr Haidong Kan (Fudan University) told theheart.org | Medscape Cardiology in an email.
Thus, the use of “air purifiers could be one of the effective ways to mitigate potential health risks on smoggy or heavily polluted days, especially for vulnerable populations” such as patients with cardiovascular disease, he suggested.
More research is needed to “examine whether these health benefits from short-term air purification could be maintained and translated into improved health in the long run,” the authors conclude.
As a next step, there is an “urgent need” for “clinical-trial evidence that taking personal-level actions (using air purifiers, wearing N95 respirators) can actually reduce hard cardiovascular events and decrease mortality in high-risk patients living in heavily polluted countries,” Dr Robert D Brook (University of Michigan, Ann Arbor), who coauthored an accompanying editorial[2] with Dr Sanjay Rajagopalan (University Hospitals, Cleveland, OH), told theheart.org | Medscape Cardiology in an email.
Changes in Air Quality With Filters
Epidemiologic studies have shown that breathing air with a high concentration of fine particles—specifically particulate matter (PM) smaller than 2.5 µm (PM2.5)—is associated with hypertension, coronary heart disease, stroke, and type 2 diabetes, but the mechanism for this is not known, Li and colleagues write.
To investigate this, they recruited healthy college students from 17 nonsmoking dormitories at Fudan University, Shanghai, from November to December 2015.
The PM2.5 level in Shanghai is around four to five times higher than in American cities, largely due to coal combustion, industry, and traffic, Kan said.
The participants were asked to refrain from cooking or housecleaning and stay in their dorms as much as possible during two 9-day study periods, which were separated by a 12-day washout.
During the air-purification treatment, a high-efficiency air purifier was placed in the middle of each dorm, and during the sham treatment the filter was removed.
The researchers determined the levels of PM2.5 for the air inside the dorms and for air in nearby outdoor places.
At the end of the two study periods, the participants provided serum samples that were analyzed for 97 metabolites using gas-chromatography-mass spectrometry and ultra-high-performance liquid-chromatography-mass spectrometry. They also provided blood and urine samples for biomarkers of inflammation and oxidative stress and had their blood pressure measured.
The 55 participants (28 men and 27 women) had a mean age of 20, mean body mass index of 21 kg/m2, and a mean BP of 106/68 mm Hg.
The outdoor air had a mean PM2.5 of 101 µg/m3. The indoor air had a PM2.5 of 46.8 µg/m3 after the sham air purification and dropped to 8.6 µg/m3 after the actual air purification.
Overall, on average the participants were breathing air with 53.1 μg/m3 of fine particles during the sham purification phase and 24.3 μg/m3 of fine particles during the actual purification phase.
This improved level of fine particles in the air “is still two to three times that faced by most Americans,” Brook and Rajagopalan write.
To put this into context, the World Health Organization air-quality guidelines recommend PM2.5 <10 µg/m3, but no threshold has been identified below which no damage to health is observed, they note.
“Peak PM2.5 levels in Chinese cities can reach astounding concentrations above 500 to 1000 µg/m3,” Brook said, and “these extraordinary levels are 10 to 20 times higher than peak pollution events seen in the US during the past few decades.”
Changes in Multiple Metabolites, Biomarkers
The participants had higher levels of serum glucocorticoids (cortisone and cortisol), catecholamine (epinephrine and norepinephrine), and melatonin at the end of the sham period.
They also had significantly higher levels of glucose, 10 amino acids, fatty acids, membrane phospholipids, insulin resistance, and biomarkers of oxidative stress and inflammation, and their blood pressure was 2.6% higher than after the air-purification period.
“This current study has helped to elucidate important ‘mediating’ pathways whereby the inhalation of PM2.5 can prompt adverse responses in cardiovascular tissues remote from the site of inhalation in the lungs,” Brook said.
The findings also add to growing evidence that high-efficiency particulate air (HEPA) filters can help protect against adverse health impacts of air pollution, but more study is needed to see whether these effects last and if filters and masks can reduce cardiovascular morbidity and mortality.
In the meantime, “as healthcare providers, we should be on the vanguard of supporting air-quality regulations in the US, Canada, Europe and across the world order to protect our patients, their families, and global public health,” Brook said.
The study was supported by grants from the National Natural Science Foundation of China; the Public Welfare Research Program of National Health and Family Planning Commission of China; the Shanghai 3-Year Public Health Action Plan; the Cyrus Tang Foundation; and the China Medical Board Collaborating Program. The editorial was supported by grants from the National Institutes of Health and the University of Michigan‒Peking University Joint Institute for Translational and Clinical Research. The authors and have no relevant financial relationships. Brook receives research grant support from RB Inc; Rajagopalan has no relevant financial relationships.
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