A concerning new study has found compelling evidence that long-term exposure to air pollution significantly increases the risk of developing dementia later in life. The research, which followed over 25,000 female nurses in Denmark for more than two decades, showed that particulate matter, nitrogen dioxide, and black carbon were all associated with higher dementia incidence. The University of Copenhagen study, which is published in the journal Alzheimer’s & Dementia, also suggested that staying physically active might help counteract these harmful effects.
Dementia is a debilitating condition characterized by progressive memory loss and cognitive decline. Common types include Alzheimer’s disease and vascular dementia. While the exact causes remain unclear, scientists believe that deposits of abnormal proteins in the brain, vascular damage, and inflammation all play a role. Recently, environmental factors like air pollution have also been implicated.
Air pollution is a pervasive public health issue, linked to a host of diseases from asthma to heart disease and lung cancer. It’s primarily composed of particulate matter (tiny particles of soot and dust), nitrogen dioxide and ozone (irritant gases), and black carbon (sooty carbon from combustion). These pollutants are so small that they can enter the bloodstream, cross into the brain, and potentially trigger inflammation, oxidative stress and even direct damage to brain cells.
While previous studies have found associations between air pollution and dementia risk, this Danish study is particularly robust due to its large sample size, detailed and historical air pollution data, and comprehensive dementia diagnoses from national health registries. Researchers used state-of-the-art air pollution models to estimate the nurses’ exposure at their exact addresses, going back 14 years before the study even began.
Researchers discovered nurses exposed to higher levels of particulate matter, nitrogen dioxide and black carbon over the course of many years had a significantly higher risk of developing dementia. For particulate matter, each increase of 2.6 μg/m3 was associated with a worrying 35 percent higher risk. Nitrogen dioxide and black carbon showed similar trends. Notably, these associations remained even after accounting for road traffic noise, which has also been hypothesized to influence dementia risk through sleep disturbance and stress. In fact, the link between road noise and dementia largely disappeared after adjusting for air pollution, suggesting that air pollution may be the more important factor.
“This is the first study in Denmark showing a link between air pollution and dementia,” says study author Zorana Jovanovic Andersen, professor at University of Copenhagen’s Section of Environmental Health. “Although air pollution levels in Denmark have been declining and are relatively low, compared of the rest of Europe and world, this study shows that there are still significant and concerning health effects that demand more action and policies towards reduction of air pollution.”
But there was a silver lining: physical activity seemed to modify the relationship between air pollution and dementia. Nurses who reported high levels of physical activity did not have an increased dementia risk associated with air pollution exposure, in contrast to nurses with lower physical activity. This suggests that staying active might offer some protection against the deleterious effects of air pollution on brain health.
Researchers speculate that physical activity may reduce overall inflammation in the body, counteracting the inflammatory effects of inhaled pollutants. Exercise is also known to stimulate the growth of new brain cells and connections, which could increase cognitive reserve and resilience. Of course, more research is needed to confirm these findings and tease out the potential mechanisms.
Air pollution poses a serious threat to brain health, and stricter regulations on emissions are needed to protect public health. However, we can’t always control the air we breathe, especially if we live in urban areas. This is where the physical activity findings offer a glimmer of hope — by staying active, we may be able to bolster our brain’s defenses against environmental toxins.
“As we are going to live longer, and more and more people will be diagnosed with dementia, this finding is important as it offer an opportunity to prevent new dementia cases, and ensure more healthy aging, by cleaning up the air we breathe,” concludes Andersen.
