It turns out COVID-19 isn’t the only reason we should be wearing face masks. People who live in polluted areas should also cover up to prevent them getting dementia, an alarming new study suggests. Researchers warn that just a single microgram per cubic meter of pollution in the air is linked with higher risk of brain disease. Living next to a shopping center compared to a park, for example, is associated with a 16 percent higher incidence of dementia.

Previous studies have shown long term exposure to air pollution can be hazardous to health leading to conditions that affect the lungs and heart. Most research has focused on a component of air pollution known as fine particulate matter or PM 2.5 — tiny particles that are 40 times smaller than the width of a human hair.

In this study, researchers from the University of Washington examined specific addresses in Seattle using data from large projects from the 1970s and 1990s and the link with a greater risk of dementia. Once a patient with dementia was identified, researchers compared the average pollution exposure of each participant leading up to the age at which the dementia patient was diagnosed. For instance, if a person was diagnosed with dementia at 72 years old, the researchers compared the pollution exposure of other participants over the decade prior to when each one reached 72.

In their final analysis, the researchers found that just one microgram per cubic meter difference between residences was associated with 16 percent higher incidence of dementia. A similar association was found for Alzheimer’s-type dementia in particular.

“We know dementia develops over a long period of time,” says lead author Rachel Shaffer, a doctoral student at the University of Washington, in a statement per South West News Service. “It takes years – even decades – for these pathologies to develop in the brain, and so we needed to look at exposures that covered that extended period. We had the ability to estimate exposures for 40 years in this region. That is unprecedented in this research area and a unique aspect of our study. 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.”

The study shows there was approximately a single microgram’s difference in pollution between Seattle’s Pike Street Market, a popular fishing marketplace, and residential areas around Discovery Park.  They believe that people who live in pollution-dense areas should consider continuing to wear masks in order to combat these ill effects.

“There are some things that individuals can do, such as mask-wearing, which is becoming more normalized now because of COVID,” says Shaffer. “But it is not fair to put the burden on individuals alone. These data can support further policy action on the local and national level to control sources of particulate air pollution.”

“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,” adds Lianne Sheppard,  a professor of health sciences and biostatistics.