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BOSTON — People living near busy roadways are much more likely to develop dementia, a recent study warns. Researchers from Harvard T.H. Chan School of Public Health say even exposure to small amounts of air pollution below current safety limits fuels cognitive decline.

The findings add to evidence that regulatory standards are not sufficiently protective and need further tightening. The results come from an analysis of more than 16 million adults, one of the biggest of its kind.

“This is a big step in providing actionable data for regulatory agencies and clinicians in terms of making sense of the state of the literature on this hugely important health topic. The results can be used by organizations like the Environmental Protection Agency, which is currently considering strengthening limits on PM2.5 exposure,” says lead author Marc Weisskopf, Cecil K. and Philip Drinker Professor of Environmental Epidemiology and Physiology, in a university release. “Our findings support the public health importance of such a measure.”

The tiny toxic particles (fine particulate matter) are the leading environmental risk factor for disease. Less than a fiftieth the width of a human hair, they get into the blood through the lungs, making it more sticky and triggering inflammation.

Sources of fine particulate matter exposure include diesel fumes, wood smoke, brake pads, tires, and road dust. The EPA’s current annual regulatory standard is 12 micrograms per cubic meter (µg/m3). However, results suggest an alarming 42-percent greater risk of dementia for every two µg/m3 increase in average concentrations.

Traffic in New York City
(Photo by Carlos Felipe Ramírez Mesa on Unsplash)

Other roadway gases can damage the brain too

Results also identified a smaller link with exposure to nitrogen dioxide and nitrogen oxide gases, also emitted by traffic and industry. More than 57 million people worldwide are living with dementia.

“Given the massive numbers of dementia cases, identifying actionable modifiable risk factors to reduce the burden of disease would have tremendous personal and societal impact,” Weisskopf adds. “Exposure to PM2.5 and other air pollutants is modifiable to some extent by personal behaviors—but more importantly through regulation.”

The study is the first to screen entire populations followed by personal evaluations for dementia among individuals who were healthy at the outset.

Professor Andrew Sommerlad, a psychiatrist at University College London, who did not take part in the project, is calling for global legislation.

“Around 40 percent of countries still have no published standards for air pollution, supporting the need for the World Health Organisation’s global air quality guidelines that proposed increasingly strict targets, ultimately aiming for average annual PM2.5 concentration of less than 5 μg/m3,” Prof. Sommerlad says, according to a statement from SWNS.

“Reductions in air pollution are theoretically achievable through global environmental policy programs that focus on transition to clean and renewable energy sources,
reduced energy consumption and changes in agriculture,” the psychiatrist continues.

“Any positive effect on dementia and general health would be accompanied by an important impact on climate change and biodiversity, therefore, reducing air pollution should be a global health and humanitarian priority.”

Air pollution has also been linked to other major life-threatening illnesses, including cardiovascular disease, cancer, and diabetes.

The findings appear in The BMJ.

South West News Service writer Mark Waghorn contributed to this report.

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