UNM researchers link heavy wildfire smoke exposure to poorer mental health measures

Millions of Americans increasingly find themselves living under a blanket of wildfire smoke for days or even weeks on end as climate change drives hotter, drier conditions, fueling conflagrations that can rage across hundreds of square miles.

That smoke is filled with ultra-fine particulate matter (PM)—a mix of solid and liquid particles in the air—measuring 2.5 micrometers or less (PM 2.5). Now, researchers in The University of New Mexico School of Medicine report that acute exposure to these particles for extended periods is associated with poorer outcomes on mental health measures.

In a paper published in the journal Respiratory Research, a team led by epidemiologist Shuguang Leng, MBBS, PhD, associate professor in the School of Medicine's Department of Internal Medicine, mapped wildfire smoke exposure across New Mexico at a 1x1 kilometer resolution, using estimated air quality data combined with satellite imagery.

The study demonstrated that, on days when wildfire smoke plumes hovered over the greater Albuquerque area, ambient PM 2.5 levels increased by an average of 60% (approximately 2.41 micrograms of particles per cubic meter of air). Along with adverse mental health effects, study subjects also experienced respiratory symptoms and breathlessness that limited their physical activity.

It takes a few weeks to get rid of those particles. Especially when you have a consistent exposure to smoke for a few days or a few weeks, it takes even longer.

- Shuguang Leng, MBBS, PhD, Epidemiologist & Associate Professor, Department of Internal Medicine, UNM School of Medicine

“It seems the impact for physical health lasts longer, compared to mental health,” Leng said. “With mental health, most of the significant results occur when you look at exposure one week prior to the questionnaire.”

Prior research has shown that the microscopic particles in wildfire smoke can lodge in tiny air sacs in the lungs called alveoli, Leng said. Immune cells called macrophages treat the particles as invaders and engulf them, releasing inflammatory molecules called cytokines that can travel throughout the body.

“It takes a few weeks to get rid of those particles,” he said. “Especially when you have a consistent exposure to smoke for a few days or a few weeks, it takes even longer. I think that might be the physiological foundation for why we see smoke effects on physical health for a few weeks.”

Leng said further research will be needed to determine why wildfire smoke exposure adversely affects mental health, but noted a study led by Matthew Campen, PhD, MSPH, Regents’ Professor in the UNM College of Pharmacy, that found persistent deficiencies of serotonin, a neurotransmitter important for mood regulation, in the brains of older mice exposed to wildfire smoke.

While the acute health effects of extreme air pollution spikes are well-known, Leng wanted to investigate the relationship between wildfire smoke exposure and health-related quality of life over time. It involved an analysis of data collected starting in 2006 in a long-running study of hundreds of current and former smokers, the majority of whom live in the greater Albuquerque area.

Participants filled out questionnaires that gauged their physical and mental well-being, as well as their social functioning. Wildfire smoke exposures were calculated for seven, 15, 30 and 60 days prior to completion of the questionnaires, using several methods to correlate the participants’ addresses with the intensity of the exposure.

Even in the absence of wildfires there is a “background” level of combustion-related PM 2.5 in the air from sources like auto exhaust and coal-fired power plants (the annual average in New Mexico is about 4-5 micrograms of particles per cubic meter of air). Wintertime use of wood-burning stoves and fireplaces can raise those levels significantly, Leng said, and plumes from wildfires may significantly amplify these effects.

Prior to passage of the Clean Air Act in 1963, many communities in the U.S. were exposed to high levels of PM 2.5. Over time conditions significantly improved, Leng said, but he warns that the growing frequency of severe wildfires threatens to halt that progress.

“In a lot of areas, you could actually see a reversal,” he said. “You get more PM 2.5 because of the wildfire smoke.”