(This version of the story refiles to change millimeters to micrometers in paragraph 2)

A man wearing a respiratory protection mask walks toward an office building during the smog after a red alert was issued for heavy air pollution in Beijing's central business district, China, December 21, 2016. REUTERS/Jason Lee

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 less than 2.5 micrometers in diameter, from industrial sources, that can be inhaled and become lodged in the lungs. While PM 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 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 period during which the filters were removed, the researchers did another nine-day test: the students in the original functioning-filter group got non-working filters, and those in the original nonfunctioning-filter group got filters that worked. At the end of each nine-day period, the researchers tested levels of a wide range of small molecules in students’ blood and urine as indication of their exposure to PM.

Students’ levels of the stress hormones cortisol, cortisone, epinephrine and norepinephrine rose with dirtier air, as did their levels of blood sugar, amino acids, fatty acids and lipids. Higher exposure to PM was also associated with higher blood pressure, a worse response to insulin, and markers of molecular stress on body tissues - all of which can, over time, increase the risk for heart disease, diabetes and other problems.

Air purification cut the amount of PM students were exposed to in half, from 53 micrograms per cubic meter of air to 24.3 micrograms per cubic meter – but that was still well above the World Health Organization’s Air Quality Guideline of 10 micrograms per cubic meter.

Dr. Robert D. Brook of the University of Michigan in Ann Arbor, who co-authored an editorial accompanying the study, told Reuters Health by email that the stress responses triggered by these small pollution particles “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.”

SOURCE: bit.ly/2vIJlJv Circulation, online August 14, 2017.