Air pollution ups stress hormones, alters metabolism
By Anne Harding
NEW YORK (Reuters Health) - Breathing dirty air causes stress hormones to spike, new research suggests, which could help explain why long-term exposure to pollution is associated with heart disease, stroke, diabetes, and a shorter life span.
Dr. Haidong Kan of Fudan University in Shanghai, China, and colleagues looked specifically at the health effects of particulate matter (PM), small particles <2.5 mm in diameter, from industrial sources, that can be inhaled and become lodged in the lungs. While PM 2.5 levels have gone down in North America in recent years, they are on the rise worldwide.
“This research adds new evidence on how exposure to PM could affect our bodies, which may (ultimately) lead to higher cardiovascular risk,” Dr. Kan told Reuters Health in an email interview. “Our result may indicate that particulate matter could affect the human body in more ways than we currently know. Thus, it is increasingly necessary for people to understand the importance of reducing their PM exposure.”
The new study, published online Auhust 14 in Circulation, included 55 healthy college students in Shanghai, a city with pollution levels in the middle range compared to other Chinese cities, according to Dr. Kan.
He and his colleagues put working or non-working air purifiers in each student’s dorm, and left them in place for nine days. After a 12-day “washout” period, the researchers swapped out the filters and left them for another nine days. At the end of each nine-day period, the researchers tested levels of a wide range of small molecules in students’ blood and urine.
Ninety-seven metabolites were associated with short-term PM exposure, the researchers found. Levels of cortisol, cortisone, epinephrine and norepinephrine rose with dirtier air. The researchers also found differences in individual participants' blood sugar, amino acids, fatty acids and lipids between the real air purification and sham air purification phases. Higher exposure to PM 2.5 was also associated with higher blood pressure, a worse response to insulin, and markers of oxidative stress and inflammation.
Air purification cut the amount of PM students were exposed to in half, from 53 mcg/m3 to 24.3 mcg/m3 – but that was still well above the World Health Organization’s Air Quality Guideline of 10 mcg/m3.
The changes observed with higher PM levels suggest that breathing polluted air activates two key mechanisms involved in the stress response, the hypothalamus-pituitary-adrenal and sympathetic-adrenal-medullary axes, Dr. Kan said. “Our results may provide potential therapy targets for clinical practitioners in preventing PM-related cardiovascular events,” he added. “On the other hand, this randomized, double-blind, crossover trial of air purification demonstrates that the use self-protection devices such as air purifiers could be one of the effective ways to mitigate potential health risks in smoggy or heavily polluted days, especially for vulnerable populations.”
Dr. Robert D. Brook of the University of Michigan in Ann Arbor, who coauthored an editorial accompanying the study, told Reuters Health by email that based on this study, “the overall extent and vast array of maladaptive stress responses triggered by PM 2.5 are larger and more varied than previously known.”
He added: “Simple actions taken at a personal level, including usage of air purifiers with HEPA filers, can substantively reduce exposures and help lessen the harmful heath effects of (PM) over a few days.”
Moving forward, he said, the findings “help set the stage for what we believe is urgently needed now - clinical trial evidence that personal-level actions (air purifiers, N95 respirators) can actually reduce hard cardiovascular events and mortality among high risk patients living in heavily polluted countries.”
“This evidence-based proof is needed to help provide clinical recommendations for the millions of people with heart diseases living in regions where the poor air quality is not likely to significantly improve over the upcoming decades,” Brook said.
“Air pollution is a global threat to the health of all humans living everywhere,” he added. “We are all at risk to the hazards of air pollution and are all at least partially responsible. It is time to move forward with cleaner ‘green’ sources of energy and transportation - for our own good and for the benefit of everyone else on the planet.”
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