Story at a glance
- New research details the association between air pollution and dementia risk.
- Even levels of fine particulate matter below the Environmental Protection Agency’s air pollution standards were linked with a heightened risk of the condition.
- Findings are based on a meta-analysis of 16 studies.
Exposure to air pollution, even at levels below American and European air quality standards, is associated with an increased risk of dementia, new study results show.
Although uncertainties remain, researchers from Harvard University say their findings “suggest consistent evidence of an association between ambient air pollution and clinical dementia.”
Fine particulate matter, or PM 2.5, has been linked with a host of health concerns including heart attacks and lower life expectancy.
The latest research is based on an analysis of 16 studies, most of which were carried out in North America and Europe. Data revealed dementia risk rose by 17 percent for every two micrograms per cubic meter (µg/m3) increase in average annual PM2.5 exposure.
The United States Environmental Protection Agency’s annual standard for PM 2.5 is 12 μg/m3, while the United Kingdom’s standard is set at 20 μg/m3, and the European Union’s at 25 μg/m3.
Limited data also suggests exposure to nitrogen dioxide and nitrogen oxide could be risk factors for dementia, raising the likelihood by 2 percent and 5 percent for every 10 µg/m3 increase in pollutant concentration, respectively. No link was found between ozone pollution and dementia risk.
Although dementia risks associated with air pollution were smaller than those for other risk factors like education and smoking, “given the size of the population that is potentially exposed to air pollutants, the population health implications can be substantial,” researchers wrote.
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Almost 10 percent of older Americans live with dementia and more than 20 percent have mild cognitive impairment. Alzheimer’s disease is the most common cause of dementia. Nearly 13 million Americans are expected to live with Alzheimer’s by 2050.
Of the more than 57 million people around the world who have dementia, up to 40 percent of these cases are thought to be linked with potentially modifiable risk factors, researchers wrote.
The findings mark “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,” said author Marc Weisskopf, professor of environmental epidemiology and physiology at Harvard, in a statement.
“Our findings support the public health importance of such a measure.”
The EPA has proposed tightening its limits from 12 μg/m3 to 9 or 10 micrograms.
The meta-analysis was the first of its kind to use a new tool that addresses bias in environmental studies in more detail than other, previously used approaches. Researchers also included newer studies that incorporated “active case ascertainment,” meaning findings are based on screenings of study populations followed by in-person dementia evaluations.
These studies tended to show a stronger association between dementia risk and air pollution than those that used more passive methods, like assessments of electronic health records.
“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 said.
“Exposure to PM2.5 and other air pollutants is modifiable to some extent by personal behaviors—but more importantly through regulation.”
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