A small increase in air pollution from small toxic particles could increase the risk of dementia

A small increase in air pollution from tiny, toxic particles increases dementia risk by 16 percent, a new study finds.

Researchers at the University of Washington used decades of data from two long-term projects in the Puget Sound region, one on dementia risk factors and one on air pollution.

In addition to the increased risk of dementia, the researchers found that the same small increase in air pollution increased Alzheimer’s risk by 11 percent.

The study suggests that improving air quality could be an important strategy to reduce dementia, especially in vulnerable neighborhoods.

Long-term exposure to air pollution may increase dementia risk, a new study from the University of Washington suggests. Pictured: The Seattle Space Needle during September 2020 wildfire season

It is well known among environmental researchers that air pollution can lead to respiratory problems ranging from asthma to lung cancer.

A particularly dangerous form of pollution is mentioned fine dust, or PM2.5 — named because the particles are 2.5 micrometers wide, about 30 times smaller than a human hair.

PM2.5 pollution is tied to car exhaust, construction sites, chimneys, fires and other sources.

This pollution has been linked to an increased risk of severe COVID-19.

Recent research has also established links between PM2.5 pollution and dementia, the decline in memory and thinking ability that seniors often experience.

A new study – published Wednesday in the journal Environmental Health Perspectives – provides evidence for this trend.

For those patients with dementia, the UW researchers examined their exposure to air pollution using past PM2.5 measurements.  Seattle's suburbs tend to have less pollution than downtown

For those patients with dementia, the UW researchers examined their exposure to air pollution using past PM2.5 measurements. Seattle’s suburbs tend to have less pollution than downtown

Researchers from the University of Washington (UW) examined decades of data on the development of dementia and air pollution in the Seattle, Washington area.

Most studies on dementia risk examine five years of data or less, making this new study unique in its long run.

The researchers used the Adult Changes in Thought (ACT) Study, a collaboration between UW and Kaiser Permanente Washington Health Research Institute to identify risk factors for dementia.

ACT researchers tracked more than 4,000 Seattle seniors for 25 years. The seniors did not have dementia when the study began, but received cognitive checkups every two years.

Of those 4,000 patients, more than 1,000 were diagnosed with dementia over the course of the study.

For those patients who were diagnosed, the researchers examined their exposure to air pollution using air quality data — measured regularly in Seattle since 1978.

Using detailed data on where the patients lived, the researchers were able to determine how much PM2.5 pollution they had been exposed to — and how that compared to the patients who did not develop dementia.

The finding was striking – a small increase in long-term exposure to pollution posed a significant risk of developing dementia.

“We found that an increase of one microgram per cubic meter of exposure corresponded to a 16 percent greater risk of all-cause dementia,” said Rachel Shaffer, lead author and doctoral student of environmental health at UW.

That amount — one microgram per cubic meter — is equivalent to the pollution difference between downtown Seattle and a remote residential area.

The researchers also found that an increase of one microgram per cubic meter led to an 11 percent higher risk of Alzheimer’s disease.

These comparisons were made over a 10-year period of exposure to pollution.

‘We know that dementia develops over a long period of time. It takes years — even decades — for these pathologies to develop in the brain, so we had to look at exposures that spanned that longer period of time,” Shaffer said.

Shaffer and other study researchers expressed their gratitude for the ACT study. The long-term data collection from this study enabled the investigation of dementia risk.

“With reliable address histories, we can get more accurate estimates of air pollution for study participants,” said Lianne Sheppard, the paper’s lead author and professor of environmental health at the UW.

Patients exposed to more air pollution over a 10-year period were more likely to develop dementia or Alzheimer's disease

Patients exposed to more air pollution over a 10-year period were more likely to develop dementia or Alzheimer’s disease

“These high-quality exposures combined with the regular follow-up of participants in ACT and standardized diagnostic procedures contribute to the potential policy impact of this study.”

This research provides important evidence for the contribution of air pollution to dementia and other neurological disorders.

In another recent study, released at the Alzheimer’s Association International Conference in July, researchers said improving air quality is an important dementia prevention strategy.

When neighborhoods are affected by pollution, the effects are widespread and far-reaching.

‘Across an entire population, a large number of people are exposed. So even a small change in relative risk eventually becomes important at the population scale,” Shaffer said.

“There are some things that individuals can do, such as wearing a mask, which is now becoming more normalized because of COVID. But it is not fair to place the burden only on individuals.

‘These data can support further policy action at local and national level to control sources of particulate matter pollution.’

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