Air pollution has been linked to an increased risk of dementia with Lewy bodies and Parkinson's disease dementia.

This large Danish case-control study, based on national registries, examined whether long-term exposure to fine particulate matter (less than 2.5 micrometers in diameter) and nitrogen dioxide was associated with the risk of two neurodegenerative conditions: dementia with Lewy bodies and dementia associated with Parkinson's disease.

The main result: higher 10-year exposure to both pollutants was associated with an increased risk of both types of dementia. The association was particularly strong for Lewy body dementia: each 5 micrograms per cubic meter increase in fine particulate matter was associated with a nearly fourfold increase in risk in the fully adjusted model.

However, the study does not prove that air pollution per se directly causes these diseases. These are observational data: the authors controlled for age, gender, calendar period, socioeconomic factors, and medical and psychiatric comorbidity, but residual confounding is still possible.

Parameter	Data
Magazine	JAMA Network Open
Date of publication	May 14, 2026
DOI	10.1001/jamanetworkopen.2026.12601
Type of study	Population-based nested case-control study
Country	Denmark
Age of participants	65-95 years old
Diagnostic period	2001-2021
Major pollutants	Fine suspended particles with a diameter of less than 2.5 micrometers and nitrogen dioxide
The main conclusion	Higher long-term exposure was associated with an increased risk of dementia with Lewy bodies and Parkinson's disease dementia

What happened?

Researchers used Danish national registries to trace the link between air pollution and rare but severe forms of dementia known as alpha-synucleinopathies. Alpha-synucleinopathies are a group of diseases in which the abnormal protein alpha-synuclein accumulates in the nervous system; they include Parkinson's disease, dementia with Lewy bodies, and Parkinson's disease dementia.

The analysis included data from 2,184,847 Danish residents aged 65 to 95. Among them, the researchers identified 3,024 individuals with Lewy body dementia and 3,808 individuals with Parkinson's disease-associated dementia; each case was matched with 10 controls of the same gender and similar age.

The authors assessed not a single air pollution exposure, but a 10-year weighted average exposure prior to diagnosis. For this, they used residential address histories and air pollution models for all of Denmark, including the Danish Eulerian Hemispheric Model and the Urban Background Model.

This approach is important because neurodegenerative diseases develop over years. If air pollution does affect the brain, it's logical to expect not an immediate effect, but rather the effects of cumulative, long-term exposure.

What was studied?	How was it assessed?
Dementia with Lewy bodies	First registered diagnosis in hospital or specialized registers
Dementia in Parkinson's disease	First registered diagnosis in national registries
Control group	10 people per case, matched by age, gender and time
Fine suspended particles	10-year average exposure by residential address
Nitrogen dioxide	10-year average exposure by residential address
Basic statistical method	Conditional logistic regression

Why is this topic important?

Dementia with Lewy bodies and Parkinson's disease dementia are disorders associated with dysfunction of the protein alpha-synuclein. These conditions can be accompanied not only by memory impairment but also by visual hallucinations, fluctuations in attention, motor symptoms, sleep disturbances, and significant loss of independence.

The authors of the article emphasize that the incidence and prevalence of alpha-synucleinopathies are increasing, and Parkinson's disease is considered one of the fastest-growing neurodegenerative diseases worldwide. As the population ages, the number of people with Parkinson's-related dementia is also growing.

Previously, data had emerged linking air pollution to Parkinson's disease, Alzheimer's disease, and hospitalizations for dementia with Lewy bodies or dementia associated with Parkinson's disease. The new study adds an important element: it separately evaluates not only fine particulate matter but also nitrogen dioxide as a potential risk factor.

It's especially important that we're talking about air pollution as a potentially modifiable factor. Individuals can't fully control air quality in a city, but public measures—transport policy, emissions control, reducing fossil fuel combustion, and urban planning—can alter the risk level at the population level.

Why the result is significant	Explanation
Serious diseases	They impair memory, movement, behavior and independence.
The population is aging	The number of people with dementia and Parkinson's disease will increase
Potentially changeable factor	Air pollution can be reduced through public measures
Two pollutants were studied	Fine particles and nitrogen dioxide
National registers were used	Large sample and almost complete coverage of the Danish population

Key results

In fully adjusted models, each 5-microgram per cubic meter increase in fine particulate matter (particulate matter) with a diameter of less than 2.5 micrometers was associated with a 3.70-fold increased risk of Lewy body dementia. For Parkinson's disease-associated dementia, the risk was 2.41-fold higher.

Nitrogen dioxide was also associated with an increased risk, but the effect was weaker. Each 10 micrograms per cubic meter increase in nitrogen dioxide was associated with a 95% increased risk of Lewy body dementia and a 14% increased risk of Parkinson's disease dementia.

When pollutants were analyzed by quintiles, that is, groups with different levels of exposure were compared, the pattern remained the same. The highest group with exposure to fine particulate matter had a more than twofold risk of Lewy body dementia and a roughly twofold risk of Parkinson's disease dementia compared to the lowest group.

When both pollutants were included in a single model, both fine particulate matter and nitrogen dioxide remained associated with the risk of Lewy body dementia. For Parkinson's disease-associated dementia, only fine particulate matter remained consistently associated, but the authors caution that the independence of these effects should be interpreted with caution, as the levels of the two pollutants were highly correlated.

pollutant	Exodus	Result in the fully adjusted model
Fine suspended particles, +5 micrograms per cubic meter	Dementia with Lewy bodies	Adjusted odds ratio 3.70
Fine suspended particles, +5 micrograms per cubic meter	Dementia in Parkinson's disease	Adjusted odds ratio 2.41
Nitrogen dioxide, +10 micrograms per cubic meter	Dementia with Lewy bodies	Adjusted odds ratio 1.95
Nitrogen dioxide, +10 micrograms per cubic meter	Dementia in Parkinson's disease	Adjusted odds ratio 1.14
Highest vs. lowest quintile of fine particles	Dementia with Lewy bodies	Adjusted odds ratio 2.31
Highest vs. lowest quintile of fine particles	Dementia in Parkinson's disease	Adjusted odds ratio 2.02

What are fine suspended particles and nitrogen dioxide?

Fine particulate matter (particulate matter) with a diameter of less than 2.5 micrometers is a very small airborne particle that can penetrate deep into the respiratory tract. In the study, it included various components: dust, soot, organic aerosols, sea salt, secondary inorganic aerosols, and other fractions calculated using an air pollution modeling system.

Nitrogen dioxide is primarily associated with fossil fuel combustion, including transportation and other urban sources. The authors emphasize that nitrogen dioxide has already been linked to the risk of Parkinson's disease and Alzheimer's disease, but its role in dementia with Lewy bodies and dementia associated with Parkinson's disease has been less well studied.

These two pollutants often coexist: in areas with higher traffic congestion and urban density, both fine particulate matter and nitrogen dioxide can increase simultaneously. In this study, their levels were indeed significantly correlated, making it difficult to separate the effects of each pollutant separately.

Therefore, the results should not be interpreted as a simple "one pollutant is to blame, another is not." A more precise interpretation is that long-term exposure to higher air pollution was associated with a higher risk of both types of dementia, and the contribution of specific pollution components requires further clarification.

pollutant	A simple explanation	Why is it important?
Fine suspended particles	Very small particles that can penetrate deep into the respiratory tract	Linked to inflammation, oxidative stress and risk of neurodegeneration
Nitrogen dioxide	Gas often associated with transportation and fuel combustion	May reflect urban and road pollution
Joint exhibition	Both pollutants are often elevated in the same places.	It is difficult to completely separate the contribution of each
10-year exposition	Average level over a long period before diagnosis	Better reflects the cumulative impact

Possible Mechanisms: How Air Pollution May Affect the Brain

The authors discuss several possible pathways. One is neuroinflammation: air pollutants can activate immune cells in the brain, including microglia, and sustain the chronic release of inflammatory molecules. Such prolonged inflammatory activity could theoretically contribute to neuronal damage.

The second possible pathway is related to oxidative stress. Pollutants can trigger the formation of reactive oxygen species, damaging cells and amplifying inflammatory cascades. This is especially important for neurodegenerative diseases, where brain cells are already vulnerable to accumulated stress.

A third possible pathway is the olfactory system. The authors note that air pollution has been linked to olfactory impairment, and olfactory dysfunction is associated with alpha-synucleinopathies. Therefore, the nasal and olfactory systems may be one of the "entrances" through which toxic exposures reach the brain.

The mechanism remains hypothetical. The study demonstrates an epidemiological link, but did not directly measure alpha-synuclein accumulation, microglial inflammation, olfactory system damage, or biomarkers of neurodegeneration in the participants.

Possible mechanism	What does this mean?
Neuroinflammation	Chronic activation of brain immune cells
Oxidative stress	Cell damage by reactive oxygen species
Olfactory pathway	Possible entry of signals or toxicants through the nasal system
Vascular effects	Pollution can affect blood vessels and blood supply to the brain.
Cumulative impact	The sum of different pollutants and environmental factors is important

Why the link is stronger for Lewy body dementia

In the study, air pollution associations were stronger for Lewy body dementia than for Parkinson's disease-associated dementia. The authors believe this may reflect differences in the biology of these conditions, although the exact mechanism remains unknown.

One possible cause is comorbid amyloid pathology. The article's discussion notes that previous studies have linked exposure to small suspended particles with a higher burden of amyloid plaques in the cortex, and this pathology is more common in dementia with Lewy bodies than in dementia associated with Parkinson's disease.

However, the authors emphasize that the observed associations with Lewy body dementia were stronger than those found in the previous Danish Alzheimer's risk study, so the amyloid mechanism alone may not explain this. It's likely that several pathological processes are at play.

This makes this work particularly important for future research. If air pollution is associated differently with different forms of dementia, then environmental risk factors should be studied not only for dementia in general, but for specific biological subtypes.

Question	What the study showed
Where the connection is stronger	In dementia with Lewy bodies
PM2.5 and Lewy Body Dementia	Almost 4-fold risk for every +5 micrograms per cubic meter
PM2.5 and dementia in Parkinson's disease	More than 2-fold risk
Possible explanation	Neuroinflammation, amyloid pathology, olfactory pathway, mixed mechanisms
What remains unknown	Why Lewy body dementia shows a stronger association

What does this mean for patients and society?

For an individual, this doesn't mean that air pollution will inevitably lead to dementia. The risk of neurodegenerative diseases depends on age, genetics, cardiovascular health, sleep, physical activity, comorbidities, medications, lifestyle, and many other factors.

But at the population level, even a modest increase in risk can be significant. Dementia with Lewy bodies and dementia associated with Parkinson's disease are associated with severe disease progression, loss of independence, increased need for care, and significant healthcare costs.

The practical implication for public health is that air quality should be considered not only as a lung and heart issue, but also as a potential risk factor for the aging brain. This strengthens the case for reducing transport emissions, controlling industrial pollutants, promoting urban greening, and monitoring air quality in densely populated areas.

For clinical practice, this doesn't yet mean a new analysis or a new dementia prevention plan. However, physicians and public health systems can consider air pollution as an environmental factor, especially when working with older adults and patients with Parkinson's disease.

Level	Possible conclusion
Patient	Air pollution is not the only cause of risk, but it is an important environmental factor
Doctor	It is important to consider the environmental context when talking about prevention.
City	Reducing emissions can be a protective measure not only for the lungs, but also for the brain.
Science	There is a need to study biomarkers, mechanisms and different subtypes of dementia
Healthcare policy	Combating air pollution may have long-term neurological benefits

Limitations of the study

The first limitation is that diagnoses of dementia with Lewy bodies and dementia associated with Parkinson's disease were primarily taken from national registries. This could have led to an underreporting of milder cases, particularly those not admitted to hospital or specialized care.

The second limitation is that the diagnosis codes were not specifically validated for this study. Furthermore, the code for dementia with Lewy bodies in Denmark was only introduced in 2008, and prior to that, diagnostic registration may have been less accurate.

A third limitation is that the researchers lacked data on some important lifestyle factors and occupational exposures. For example, they were unable to account for occupations with increased exposure to pollutants, as well as certain behavioral factors that may influence dementia risk.

The fourth limitation is that the data were obtained in a single country. Pollution levels, urban structure, transportation, healthcare systems, and social factors in Denmark may differ from those in other countries, so the results need to be confirmed in other populations.

Limitation	Why is this important?
Registry diagnoses	There may be underreporting of mild or unrecognized cases
Diagnostic codes	Incomplete specificity of individual diagnoses is possible
Not all lifestyle factors	Residual confounding factors remain possible
No professional exposure	Working with contaminants may have influenced the risk
One country	Confirmations are needed in other systems and regions
Observational design	Association does not equal proven causation.

Result

A new study in JAMA Network Open found that long-term exposure to fine particulate matter and nitrogen dioxide was associated with an increased risk of Lewy body dementia and Parkinson's disease-associated dementia in older Danish residents.

The strongest result concerned fine particulate matter: each increase of 5 micrograms per cubic metre was associated with a 3.70-fold risk of Lewy body dementia and a 2.41-fold risk of Parkinson's disease dementia after accounting for socioeconomic factors, comorbidity and other variables.

Nitrogen dioxide was also associated with an increased risk, particularly for Lewy body dementia. In a fully adjusted model, a 10 microgram per cubic meter increase in nitrogen dioxide corresponded to a 95% increased risk of Lewy body dementia and a 14% increased risk of Parkinson's disease dementia.

The correct wording of the news is as follows: air pollution has not been proven to be the sole or direct cause of these forms of dementia, but it appears to be an important environmental factor that may influence brain health during aging. The authors believe that further research into the mechanisms is needed, particularly neuroinflammation, the olfactory pathway, and the interactions between different pollutants.

News source: Davydow DS et al. Exposure to Air Pollutants and Lewy Body and Parkinson Disease-Related Dementias. JAMA Network Open. 2026;9(5):e2612601. DOI: 10.1001/jamanetworkopen.2026.12601.