© Shutterstock

Air pollution and dementia -

Can atmospheric pollution trigger dementia? A group of scientists believe it can. In fact, elevated levels of a type of air pollution called PM2.5 have been linked to a higher number of dementia cases developing over time.

© Shutterstock

Dangers of air pollution -

Air pollution has long been identified as a threat to human health. Studies have shown it is involved in causing cancer, heart disease, diabetes, low birth rates, and a raft of other health issues.

© Shutterstock

Different types of air pollution -

Research undertaken by scientists at the University of Michigan in 2023 examined the links between different types of PM2.5 air pollution and dementia.

© Shutterstock

What is PM2.5? -

PM2.5 is the measurement given to fine particulate matter in the air so small that they can travel deeply into the respiratory tract, reaching the lungs, causing short-term health effects such as eye, nose, throat, and lung irritation, coughing, sneezing, runny nose, and shortness of breath.

© Shutterstock

Worrying statistics -

The university's Health and Retirement Study collated data from more than 27,000 adults aged 50 and older. The team found that 4,105 of the people studied—15%—developed dementia during the follow-up period.

© Shutterstock

Those at risk -

Those diagnosed with dementia were more likely to be non-white, to have less formal education, less wealth, and, crucially, to live in places with higher levels of PM2.5.

© Shutterstock

Specific sources of PM2.5 -

As part of the study, researchers also examined in detail nine specific sources of PM2.5.

© Shutterstock

Agriculture -

Smoke from agricultural fires, the deliberate burning of harvest residue by farmers, was identified as a source of PM2.5.

© Shutterstock

Road traffic -

Another source of PM2.5 is road traffic, specifically vehicle exhaust fumes.

© Shutterstock

Nonroad traffic -

Nonroad traffic, for example, industrial and agricultural vehicles and off-highway motorized machines, also serve as a source of PM2.5.

© Shutterstock

Burning coal for energy and industry -

Coal-burning power plants are a major source of fine particulate matter air pollution.

© Shutterstock

Residential wood burning -

Residential wood burning is one of the largest direct sources of PM2.5. In fact, open fireplaces without outdoor air intake emit more PM2.5s than road dust and wildfires.

© Shutterstock

Wildfires -

Smoke from wildfires, however, significantly worsen ambient air quality and constitute another major source of PM2.5 emissions.

© Shutterstock

Windblown dust -

Windblown dust, whether off land or road surfaces, contributes to high PM2.5 concentrations.

© Shutterstock

Pollen dust -

Pollen dust also contributes towards air pollution and is, of course, a familiar allergen.

© Shutterstock

Agriculture and wildfires -

After consideration from all sources, researchers concluded that PM2.5 from agriculture and wildfires were specifically associated with an increased risk of dementia.

© Shutterstock

The world's on fire! -

Exacerbating the problem is the fact that smoke pollution from wildfires may be killing an extra 12,000 people a year, new research suggests. A study, carried out by scientists at Japan's National Institute for Environmental Studies and published in the journal Nature Climate Change, estimated that in the 2010s almost 100,000 people died each year from breathing smoke from fires that contain PM2.5.

© Getty Images

Francis Crick Institute -

In 2024, a similar study to that carried out in Michigan was launched by scientists at the Francis Crick Institute, a world-renowned biomedical research center in London. They asked the same question: does air pollution cause dementia?

© Shutterstock

Examining the processes that lead to dementia -

A research project, titled Rapid, which is being funded by the charity Race Against Dementia in partnership with the Rosetrees Trust, has set out to examine the exact processes by which tiny polluting particles can lead to dementia.

© Shutterstock

Miniscule and sinister -

The minuscule fragments of solids and liquid droplets that constitute PM2.5 are less than 2.5 millionths of a meter in diameter—about 30 times finer than a human hair.

© Shutterstock

How PM2.5 gets into the brain -

Researchers investigating the correlation between air pollution and dementia suggest PM2.5s are inhaled and get into the brain through the olfactory bulb, a rounded mass of tissue that sits above the nasal cavity and plays a key role in processing smell information.

© Getty Images

How PM2.5 affects the brain -

Once in the brain, it is thought PM2.5s hitch a ride with immune cells in the central nervous system and, in their wake, neurodegeneration begins to set in. Exactly how this process unfolds and leads to dementia is not clear. It's one of the many strands of inquiry the Rapid project has set out to determine.

© Getty Images

Promoting Alzheimer's disease -

However, researchers at Crick believe any one of three different mechanisms is responsible for air pollution triggering dementia. Perhaps PM2.5s are speeding up the process by which proteins get clumped together in the brain? This can promote the onset of Alzheimer's.

© Shutterstock

Neurodegenerative consequences -

On the other hand, are PM2.5s  interfering with the body's cell clearance system? This would make it harder to clear other proteins that cause diseases, again including Alzheimer's.

© Shutterstock

Driving the onset of dementia -

A third theory is that PM2.5s are being picked up by the brain's immune cells, called microglia (pictured). This could cause these cells to trigger inflammation, which drives the onset of dementia.

© Shutterstock

A polluted planet -

These mechanisms are currently being studied in greater detail. And while the connection between air pollution and dementia needs to be better understood, there are currently over 55 million people worldwide living with the disease. This number will almost double every 20 years, reaching 78 million in 2030 and 139 million in 2050, according to Alzheimer's Disease International.

© Getty Images

More set to be diagnosed with dementia -

And by 2050, the population of people aged 65 and older—the age group most likely to be stricken by the disease—will double to 2.1 billion, suggests the World Health Organization.

© Shutterstock

Risk factors -

Indeed, the scale of dementia represents a global mental health crisis. In 2020, the peer-reviewed general medical journal The Lancet published a set of 12 "potentially modifiable risk factors" for dementia. Besides age, these are: less education, hypertension, hearing impairment, smoking, obesity, and depression.

© Shutterstock

More risk factors -

The list continues, highlighting physical inactivity, diabetes, low social contact, excessive alcohol consumption, traumatic brain injury, and air pollution.

© Shutterstock

Preventative measures are the way forward -

With regards to air pollution, "taking preventive measures to reduce air pollution and introducing behavioral interventions to reduce people's exposure to pollutants is advisable," recommends a 2024 study published by BioMed Central (BMC). 

Sources: (National Institutes of Health) (The Guardian) (Alzheimer's Society) (News-Medical) (BMC) (Nature Climate Change) (Alzheimer's Disease International) 

See also: 30 of the best ways to improve your mental health. 

© Shutterstock