A new study finds that long-term exposure to air pollution — even at low levels — may result in brain damage leading to cognitive impairment and other serious neurological conditions.
The research, led by Dr. Elissa H. Wilker, of the Cardiovascular Epidemiology Research Unit at Beth Israel Deaconess Medical Center and the Harvard T.H. Chan School of Public Health in Boston, MA, is published online ahead of print in the journal Stroke.
The health risks of exposure to air pollution are well documented. Besides the direct physical effects of breathing in harmful air — which include asthma, cardiovascular disease and even cancer — studies also show that exposure to air pollution increases the risk for a host of mental health problems ranging from suicide and schizophrenia to ADHD and autism.
Of particular concern is fine particle air pollution, which is implicated as the causal agent in many of these adverse health conditions. Found in smoke and haze from car exhausts, burning wood and power plants, fine particle air pollution is defined as particulate matter that is 2.5 micrometers or less in diameter (PM2.5).
This form of air pollution is a major health concern, as small particles can easily pass through the throat and nose and get deep into the lungs, causing major health problems.
Long-term PM2.5 exposure particularly harmful to older people
For the new study, Dr. Wilker’s team set out to assess the effects of long-term exposure to PM2.5 on brain structure. Using magnetic resonance imaging (MRI), the researchers analyzed the brains of 943 healthy adults free of stroke and dementia who were enrolled in the Framingham Offspring Study.
All participants lived in greater Boston, New England or New York — areas where pollution levels are low compared with other parts of the U.S. — and the MRI scans were conducted between 1995 and 2005.
The researchers found that an increase in PM2.5 of 2 micrograms per cubic meter of air (μg/m3) — a pollution range common across metropolitan regions — was linked to a 0.32 percent reduction in total cerebral brain volume, as well as a 46 percent increased risk of a type of silent stroke known as covert brain infarcts.
“Long-term exposure to air pollution showed harmful effects on the brain in this study, even at low levels, particularly with older people and even those who are relatively healthy,” explains Dr. Wilker.
The reduction in brain volume observed in the participants is comparable to around 1 year of brain aging, the researchers said, and changes in brain structure and a reduction in its volume are indicators of age-related brain atrophy. The covert brain infarcts, which Dr. Wilker says normally occur in regions deep in the brain, have been linked to poorer cognitive function, dementia and other neurological problems, and are believed to be associated with small vessel disease.
“These results are an important step in helping us learn what is going on in the brain,” Dr. Wilker says. “The mechanisms through which air pollution may affect brain aging remain unclear, but systemic inflammation resulting from the deposit of fine particles in the lungs is likely important.”
The new findings support previous studies that have linked long-term exposure to air pollution and residing close to busy roads with reduced cognitive function in seniors and first-time stroke. Alarmingly, similar brain changes have also been observed in children with prolonged exposure to air pollution.
While avoiding all air pollution is not realistic, experts say the public should understand that there are health risks to living in polluted environments, particularly for older adults, and we should all be more aware of issues related to air quality.
The good news is that, unlike other factors that may be involved in the development of dementia and age-related cognitive decline, such as diet and physical activity, air pollution is something we can intervene on as a society at large through policy, regulation and technology. Efforts focused on air pollution reduction may be a promising means for reducing the future population burden of age-related cognitive decline, and eventually, dementia.