News Coverage

28 February 2024

HARVARD MAGAZINE: How Air Pollution Affects Our Brains

Category: News Coverage

EMERGING EVIDENCE shows that exposure to air pollution increases the incidence and progression of Alzheimer’s, Parkinson’s, and other neurocognitive diseases, according to Francesca Dominici.

She spoke as part of a panel on how air pollution affects the human brain, held February 27 at the Harvard T. H. Chan School of Public Health (HSPH). Dominici, one of world’s leading data scientists studying the health effects of fine particles, was joined on the panel by Joseph Allen, an expert on indoor air pollution; Maite Arce, president and CEO of the Hispanic Access Foundation; and Marc Weisskopf, who studies the biological mechanisms that make PM 2.5 (particles that are 2.5 microns or smaller in diameter) deadly. The group discussed both outdoor and indoor air pollution, the physiological pathways particles travel within the human body, their mental health effects, the elevated impacts on underprivileged groups in the United States, and the Environmental Protection Agency’s (EPA) new fine particle regulations.

Dominici, the Gamble professor of biostatistics, population, and data science, has been working with HSPH colleagues to analyze the healthcare records of millions of Americans in the Medicare and Medicaid programs, and linking them to each person’s long-term exposure to fine particle pollution. “What we are finding, with enormous statistical power,” she said, “is that long-term exposure to fine particulate matter increased the incidence of hospitalization for Alzheimer’s disease.” It also accelerates the progression of the disease, as well as the rate of hospitalization and mortality from all causes.

Why are fine particles so biologically dangerous? “The exploration of air pollution and the brain is relatively new,” Weisskopf said. The “wealth of data” and research documenting the cardiovascular effects of inhaled fine particles, much of it conducted at HSPH, sparked interest in the possibility that the brain, which is “hugely dependent” on the blood supply, might also be affected, he continued. Particles can generate inflammatory immune responses in the systemic circulation, according to Weisskopf, Drinker professor of environmental epidemiology and physiology, which can then affect the brain. But fine particles may be able to reach the brain directly, he continued: “When you breathe in through your nose, you’re smelling things because you have neurons that are kind of sticking out in the world, exploring it that way. And we now understand that some particles, or aspects of particles, can actually get transported directly back into the brain—skipping the lungs and the cardiovascular system.” The precise biological pathways, he said, are an active area of research.

Air pollution also affects mental health, explained associate professor of exposure assessment science Joseph Allen. An HSPH program studying the research into this link, largely in children, he said, has found that “air pollution is linked to anxiety and suicide ideation, as well as pediatric hospitalizations for pediatric disorders.”

Allen’s own work focuses on indoor air quality. One of his double-blind studies of office workers introduced chemicals off-gassed by dry cleaning and dry-erase markers into environmentally controlled workspace. During such exposure, office workers performed worse on tests of cognitive function, such as seeking and utilizing information, as well as on tests of strategic decision-making, and response to a crisis. A second study that assessed the impact of air pollution penetrating a building from outside and affecting workers at their desks demonstrated similar outcomes. As Allen summarized the research, “In all these dimensions—in office workers, university workers, kids in elementary school, high school students—we see over and over the impacts of air pollution on the whole range of mental health, from anxiety all the way through higher order cognitive function.”

SABRINA SHANKMAN, a Boston Globe reporter who moderated the event, then asked about the disparate impact of air pollution on communities of color. Dominici recalled that in one of her studies of air pollution by U.S. census tract, published three years ago in Nature, she and her colleagues found higher percentages of underrepresented minorities in the most polluted areas. Such pollution has decreased substantially due to the Clean Air Act, she noted—but strikingly, the racial disparities crossed socioeconomic lines. “Very surprising to me,” Dominici said, “was that high socioeconomic status black Americans” were exposed to higher levels of air pollution than the “lowest socioeconomic status white Americans.” She continued, “That tells you a lot about systemic bias and racism.” The reason, she believes, is less pressure from local communities on siting decisions and less attention to enforcement of EPA fine particle regulations. Such disparities are not just artifacts of historic practices such as redlining. “A study that we are conducting right now on exposure to air pollution from cryptocurrency data mining, which is not regulated in the United States,” Dominici said, indicates that the buildings that house these energy-intensive operations tend to be located in lower socioeconomic status and underrepresented minority neighborhoods, where there is less knowledge and pressure from citizens and local governments.

Maite Arce, of the Hispanic Access Foundation, has been trying to change that dynamic in Latino communities through a program called “The Air That We Breathe.” The effort has recruited citizen scientists from 12 communities who are talking about air pollution and learning from experts in air quality. The program is deploying sensors in churches to monitor and report local air quality; the data gathered are then entered into an online map. Because “we’re starting at zero in terms of the knowledge” about PM 2.5, Arce said, local leaders are developing materials tailored to the needs of their primarily Spanish-speaking or immigrant communities. They’re disseminating that information through “sermons…, film screenings, roundtables, community workshops, radio and social media.” And they help residents prepare to react on days of poor air quality through masking or staying indoors. Parents understand that airborne pollution “may increase respiratory infections in children, which can lead to symptoms like asthma, and that can lead to school absences,” she reported. But the understanding that proceeds from this public health education is “eye-opening for them, and makes them feel that urgency to take action,” Arce said, “…to really urge for policy change.”

THE CONVERSATION then turned to the new EPA fine particle regulations, which reduce the standard for U.S. air pollution from 12 micrograms of particles per cubic meter of air to nine. Dominici called this “the biggest public health victory in a long time” and expressed pride in HPSH’s instrumental role in the decision, stretching from the early “Six Cities” study 30 years ago to the most recent research. States will have to develop action plans and examine the inventory of local sources of particle pollutants, from traffic, industry, or power plants, she explained. The result will be “longer life for everybody, so it’s really good, a fantastic victory.”

On the other hand, there is no safe level of particle pollution—the cleaner the air, the healthier are the people who breathe it, the data show—so the standard could have been lower. “One might ask, well, why not zero?” she asked. “But that is nearly impossible because there is always going to be some background fine particulate matter.” Dominici characterized the new standard—nine micrograms per cubic meter—as “a compromise between the science and the political landscape.” Weisskopf, who served on the panel that recommended the new standard, provided some insight into “how the sausage gets made.” Some of the decision-makers on the panel argued for a higher number, while he and other public health advocates pushed for lower exposures. Paradoxically, a lot of the best data showing the health benefits of even lower exposures come from Canada, which has cleaner air than the United States. But the panel favored U.S. evidence, so demonstrating the value of an even better standard was difficult. The World Health Organization, he noted, suggests a target of five micrograms of fine particle pollutants per cubic meter.

Given that context, Allen segued to the “major disconnect” between the legally enforceable limits on particles outdoors, and those applying indoors. The Occupational Safety and Health Administration (OSHA) standard for workplaces, currently 5,000 micrograms per cubic meter, is more than 500 times the outdoor standard. That limit is “grossly out of date,” he said, a fact that OSHA acknowledges. The agency does enforce lower standards for chemicals, silica, asbestos, and other hazardous materials, but lacks the legal authority to set standards outside the workplace. In other words, Allen said, there is no national indoor air quality standard for all the places where OSHA doesn’t have oversight: classrooms, offices, and so on. Nor are there sufficient data about the long-term effects of indoor air pollution—even though that is where most exposures occur, because people spend most of their time indoors. “A loose collection of researchers” is trying to raise funds for such studies, he reported, but with no encompassing regulatory authority to enforce standards it’s unclear how such data might be used.

Well-designed buildings can cut indoor exposure to dangerous levels of outdoor air pollution to well below the EPA standard, as occurred during last summer’s wildfires. Allen said that even retroactively fitted high quality air filters can dramatically improve indoor air in schools, offices, and homes during such events, which are expected to increase in frequency with climate change. Weisskopf added that more research is also needed on the toxicity of various indoor air pollutants; a recent study implicated wildfire smoke, which can penetrate indoors, in dementia. More work needs to be done to assess the toxicity of other types of particles, he emphasized, because their chemical composition varies depending on their source (a gas stove, an oil-filled cooking skillet, a farm engaged in agricultural burning, or something else entirely), as may the physiological effects.

Shankman brought the event to a close with a final question for each of the panelists: “If you could change one thing today to improve air quality what would it be?”

  • “Expand the number of citizen scientists in the most affected communities,” Arce said.
  • “Get the standards changed for how we design and operate buildings,” Allen said.
  • “Shut down all the coal-fired power plants,” Dominici said.
  • “Lower the [EPA] standard further,” Weisskopf said.

And with that, the audience dispersed, trading the well-ventilated environs of HSPH for the ambient air of Huntington Avenue and the nearby Mission Hill neighborhood.

Written by Jonathan Shaw for Harvard Magazine. 


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