A major study that scanned the brains of more than 4,000 people in Maastricht, Netherlands shows that exposure to higher levels of air pollution is associated with having a smaller brain. A researcher says that the study could not find any association between air pollution and cognitive functioning, but a study in a city with more air pollution might find such an association.
Air pollution has many adverse consequences. It increases the risk of developing lung disease and cardiovascular disease, and now a new study shows that it is associated with brain atrophy.
The research contributes to understanding what negatively affects the brain and perhaps increases the risk of developing dementia – and what society can do about this.
“In addition to individual risk factors for developing dementia, there are some common risk factors, such as air pollution, which individuals cannot do anything about but society should strive to reduce,” explains a researcher behind the study, Sebastian Köhler, Professor, Department of Psychiatry and Neuropsychology, Maastricht University, Netherlands.
The research has been published in Environment International.
Indications of the association between air pollution and dementia
Sebastian Köhler’s research group focuses on risk factors for cognitive decline and dementia and how to reduce this risk. The group developed a model for the association between lifestyle and brain integrity that can estimate the degree of cognitive decline and the risk of dementia based on various parameters.
For many years, these researchers have focused on individual risk factors for dementia, such as diet, exercise, smoking and alcohol consumption, but in the new study they aimed to learn more about risk factors that could be more important at the population level than at the individual level.
One of these risk factors could be ambient air pollution.
Previous studies indicated that exposure to higher air pollution may be associated with the risk of cognitive decline and dementia. However, some of these studies originate from large cities such as Mexico City or Rio de Janeiro with extremely high air pollution.
In the new study, the researchers therefore aimed to find whether there were any differences between exposure to high versus low air pollution in Maastricht, which generally has much lower air pollution than in Mexico City or Rio de Janeiro.
“Previous studies have indicated an association, but some studies have suggested the opposite. More research results are therefore needed to elucidate a possible association,” says Sebastian Köhler.
Data on 4,002 people
The study examined data from the Maastricht study, in which 4,002 participants underwent brain scanning and completed a questionnaire to assess their cognitive functioning.
The researchers compared cross-sectional data from the study with national data for air pollution in the areas in which the participants lived.
They thereby determined whether living in areas with higher air pollution was associated with more symptoms of cognitive decline and lower cerebrospinal fluid volume as a sign of brain atrophy and the health of the capillaries in the brain.
The researchers examined air pollution based on particulate matter with an aerodynamic diameter of less than 10 µm (PM10) and less than 2.5 µm (PM2.5), nitrogen dioxide and soot.
“We can easily find a biological explanation for a possible association, since studies have shown that fine particulate matter can penetrate the blood–brain barrier and thereby enter the brain and potentially cause damage. With this study, we aimed to determine whether any association has a negative effect,” explains Sebastian Köhler.
Air pollution associated with brain atrophy
The research revealed that air pollution definitely affects the brain. The brain scans showed that the participants who lived in areas with the most air pollution had more cerebrospinal fluid in their brains.
According to Sebastian Köhler, this shows that their brains have atrophied more than among the participants living in areas with less air pollution, since more cerebrospinal fluid entering the brain indicates atrophy. Otherwise, the brain would rattle around loosely in the skull.
However, cognitive functioning did not differ significantly between participants from areas with high versus low air pollution, and the brain’s vascular integrity was not different.
May be much worse in cities with more pollution
According to Sebastian Köhler, several interesting perspectives arise from the results. First, he finds air pollution appearing to result in brain atrophy to be important.
Although the study did not find any association with cognitive decline, Sebastian Köhler says that a shrinking brain cannot be healthy.
“Our participants were 40–75 years old and still relatively young. This means that the effect of air pollution on cognitive functioning may not have been definitely established. This study is only a snapshot, and it will be interesting to see what happens over the next decade and whether the effects of air pollution on cognition become more apparent,” he says, pointing out that Maastricht is not the world’s most polluted city.
“Carrying out the same study in a more polluted city might show much greater effects on both cerebrospinal fluid and cognition,” notes Sebastian Köhler.
Including air pollution in WHO recommendations on dementia?
Sebastian Köhler says that the study contributes to understanding that promoting brain health is not just an individual matter but should also be a concern of politicians when considering greener areas, less vehicular traffic and healthier air in cities.
In addition to the presumably beneficial effect on the brain, such measures will also affect the risk of developing cardiovascular disease and lung diseases such as chronic obstructive pulmonary disease.
“WHO is preparing recommendations on dementia. I am participating in shaping these recommendations, and we are examining whether air pollution should be included in the recommendations and what countries should do to reduce air pollution,” concludes Sebastian Köhler.
