Air Pollution with Fine Particulates is Linked to a Higher Risk of Dementia

University of Washington researchers discovered a relationship between air pollution and dementia using data from two big, long-running study projects in the Puget Sound region, one that began monitoring air pollution in the late 1970s and the other on risk factors for dementia that began in 1994.

A slight rise in fine particle pollution levels (PM2.5, or particulate matter 2.5 micrometers or smaller) averaged over a decade at certain locations in the Seattle region was linked to a higher risk of dementia for persons living there, according to the UW-led study.

“We found that an increase of 1 microgram per cubic meter of exposure corresponded to a 16% greater hazard of all-cause dementia. There was a similar association for Alzheimer’s-type dementia,” said lead author Rachel Shaffer, who conducted the research as a doctoral student in the UW Department of Environmental & Occupational Health Sciences.

Having reliable address histories let us obtain more precise air pollution estimates for study participants.

Lianne Sheppard

“The ACT Study is committed to advancing dementia research by sharing its data and resources, and we’re grateful to the ACT volunteers who have devoted years of their lives to supporting our efforts, including their enthusiastic participation in this important research on air pollution,” said Dr. Eric Larson, ACT’s founding principal investigator and a senior investigator at KPWHRI.

Example of air pollution

The Adult Changes in Thought (ACT) Research, administered by Kaiser Permanente Washington Health Research Institute in cooperation with UW, looked at more than 4,000 Seattle-area people participating in the study, which was published Aug. 4 in the journal Environmental Health Perspectives. More than 1,000 inhabitants have been diagnosed with dementia at some time since the ACT Study began in 1994, according to the researchers.

Researchers analyzed the average pollution exposure of each participant leading up to the age at which the dementia patient was diagnosed after a dementia patient was discovered. For example, if a person was diagnosed with dementia at the age of 72, the researchers examined the pollution exposure of other individuals in the decade leading up to 72.

Because air pollution has decreased considerably in the decades since the ACT project began, the researchers had to account for the varied years in which these participants were included in the study.

The researchers discovered that even a 1 microgram per cubic meter difference between households was related with a 16 percent increased prevalence of dementia in their final study. In 2019, the difference in PM2.5 pollution between Pike Street Market in downtown Seattle and the residential districts around Discovery Park was around 1 microgram per cubic meter, according to Shaffer.

“We know dementia develops over a long period of time. It takes years evendecades for these pathologies to develop in the brain, and so we needed to look at exposures that covered that extended period,” Shaffer said. “We have the ability to predict exposures over 40 years in this region because of long-term work by several UW academics and others to establish thorough databases on air pollution in our region. This is a first in this field of research and a distinctive feature of our research.”

Other research strengths included extended address histories and high-quality processes for dementia diagnosis for ACT Study participants, in addition to substantial air pollution and dementia data for the region. Dementia is the sixth biggest cause of mortality globally, as well as one of the primary causes of impairment and reliance among the elderly.

Dementia has medical, psychological, social, and economic consequences for dementia patients, as well as their caregivers, families, and society at large. Dementia is frequently misunderstood and stigmatized, leading in delays in diagnosis and treatment.

“Having reliable address histories let us obtain more precise air pollution estimates for study participants,” said senior author Lianne Sheppard, a UW professor of environmental and occupational health sciences and of biostatistics. “These high-quality exposures combined with ACT’s regular participant follow-up and standardized diagnostic procedures contribute to this study’s potential policy impact.”

While numerous variables, such as food, exercise, and heredity, have been linked to an increased risk of dementia, air pollution is now acknowledged as one of the most important possibly modifiable risk factors. The latest findings from the University of Washington add to the growing body of data showing air pollution has neurodegenerative consequences and that lowering people’s exposure to air pollution might help lessen dementia burden.

“How we’ve understood the role of air pollution exposure on health has evolved from first thinking it was pretty much limited to respiratory problems, then that it also has cardiovascular effects, and now there’s evidence of its effects on the brain,” said Sheppard, who this year was awarded the Rohm & Haas Endowed Professorship of Public Health Sciences.

“Over an entire population, a large number of people are exposed. So, even a small change in relative risk ends up being important on a population scale,” Shaffer said. “Individuals can do some things, such as wear masks, which is becoming increasingly common as a result of COVID. However, putting the burden solely on people is unjust. These findings can be used to inform future policy decisions at the local and national levels aimed at reducing sources of particle air pollution.”

Magali Blanco, Joel Kaufman, Timothy Larson, Marco Carone, Adam Szpiro, and Paul Crane of the University of Washington; Ge Li of the VA Puget Sound Health Care System and UW; Sara Adar of the University of Michigan; and Eric Larson of the University of Washington School of Medicine and Kaiser Permanente Washington Health Research Institute are among the co-authors.

Multiple funds from the National Institute of Environmental Health Sciences, the National Institute on Aging, the UW Retirement Association Aging Fellowship, the Seattle branch of the Achievement Rewards for College Scientists Foundation, and others supported this research.