A great deal of data is available on the link between air pollution and people’s respiratory and cardiovascular health. Evidence exists for different compounds, whether short term or long term. In a more original way, data now also exist on the link between atmospheric pollution and cognitive functions. How do atmospheric pollutants access the central nervous system despite the blood-brain barrier? What are their effects on the brain?
What is air pollution? The atmospheric pollution is characterized by the presence in theair that we breathe in compounds that are toxic to humans or to the environment. For some compounds, the toxicity is dose-dependent; for others it is not. In addition, certain pollutants react with each other to form a new compound, which is also toxic. L’World Health Organization established thresholds not to be exceeded for six major pollutants including fine particles (<2.5 μm) and carbon dioxidenitrogen. In France, since the 2000s, the concentration of these compounds has been constantly decreasing. Nevertheless, the population remains exposed to levels that can be harmful to health.
How does polluted air affect cognitive functions?
On the one hand, there is a distance effect. The pollutants are deposited in the respiratory system triggering an inflammatory reaction with the production of cytokines. These cytokines spill into the general circulation, pass the blood-brain barrier (BHE) and end up in the brain. On the other hand, there is a direct effect. The finest particles could access the brain via nasal passage through nerve olfactory. However, the mechanisms themselves have not yet been elucidated.
What are the effects of air pollutants on the brain?
Prolonged exposure to fine particles accelerates cognitive decline and dementia. On the other hand, a direct link could not be established between exposure to nitrogen dioxide and cognitive aging.
A recent french study was conducted and included 9,294 participants over the age of 65, 61% of whom were women. The subjects underwent a cognitive examination 2, 4, 7, 10 and 12 years after inclusion. Exposure to three pollutants (fine particles, carbon soot and nitrogen dioxide) was assessed using statistical models from satellite data. Exposure to fine particles increased the dementia risk while no statistical link could be demonstrated with nitrogen dioxide and carbon soot.
These initial results deserve to be confirmed by larger trials. In addition, it is necessary to develop more effective measurement methods in order to be able to precisely quantify the exposure to atmospheric pollutants of subjects according to their mode of transport, their place of work, their way of life, etc.
Interested in what you just read?