Exposure to fine particulate matter air pollution may increase risk for dementia: study

Air pollution is increasingly becoming one of the most concerning public health challenges of our time. We are acutely aware of the dangers it poses to our lungs, contributing to respiratory illnesses, cardiovascular problems, and other physical ailments.

However, a new study published in JAMA Neurology has now revealed an alarming new consequence of long-term exposure to fine particulate matter (PM2.5): it may not only harm our lungs but also our brains, exacerbating dementia and Alzheimer’s disease. This finding is particularly worrisome for countries like India, where air quality frequently exceeds safe levels and has often been listed among the most polluted countries of the world. 

This kind of exposure to hazardous air can have significant long-term effects. According to the World Health Organisation (WHO), air pollution is a major global health threat, contributing to the deaths of around seven million people each year. Fine particulate matter leads to a variety of diseases, including stroke, heart disease, lung cancer, chronic obstructive pulmonary disease, and respiratory infections such as pneumonia. Both outdoor and indoor pollution are harmful, and pollutants include not only particulate matter but also carbon monoxide, ozone, nitrogen dioxide, and sulphur dioxide.  

The recent JAMA Neurology study now shows that long-term exposure to fine particulate matter (PM2.5) is not only associated with a higher risk of dementia but may also intensify the brain damage linked to Alzheimer’s disease. The findings make it clear that tackling air pollution is not just about protecting our lungs - it is equally about safeguarding our cognitive health and future well-being. 

What is dementia?

Dementia is a term for “several diseases that affect memory, thinking, and the ability to perform daily activities.” The condition progressively worsens over time and mainly affects older adults, although younger people can develop dementia as well. Dementia arises from the destruction of nerve cells and damage to brain structures, with Alzheimer’s disease being the most common form. Other forms include vascular dementia, dementia with Lewy bodies, and frontotemporal dementia. Dementia may also develop following a stroke, infections such as HIV, repeated brain injuries, harmful use of alcohol, or nutritional deficiencies.  

According to WHO, approximately 5.7 crore people were affected by dementia in 2021, over 60 per cent of whom lived in low- and middle-income countries. Nearly 1 crore new cases are diagnosed annually, with Alzheimer’s disease accounting for 60 to 70 per cent of these cases.  

Dementia is the seventh leading cause of death globally and a major contributor to disability and dependency among older adults. Women are disproportionately affected by dementia, both directly and indirectly. Women experience higher disability-adjusted life years and mortality due to dementia, but also provide 70 per cent of care hours for people living with dementia. 

Risk factors for dementia are wide-ranging and include age, high blood pressure, high blood sugar, obesity, smoking, excessive alcohol consumption, physical inactivity, depression, and social isolation. Environmental factors, particularly exposure to air pollution, have emerged as an additional contributor. 

Symptoms of dementia can vary, but often begin subtly. Early signs may include forgetfulness, misplacing items, getting lost in familiar places, losing track of time, difficulty solving problems, and trouble following conversations or finding words. Mood and personality changes, including anxiety, depression, withdrawal, or irritability, may appear even before memory loss becomes pronounced. As dementia progresses, individuals may require assistance with daily activities, experience difficulties in mobility, lose control over bladder and bowel functions, and display behavioural changes such as aggression. Each case of dementia is unique, depending on the underlying cause, preexisting cognitive function, and other health conditions. 

Although there is no cure for dementia, interventions can help maintain quality of life. Medications such as cholinesterase inhibitors, including donepezil, are used to treat Alzheimer’s disease, while NMDA receptor antagonists like memantine are prescribed for severe Alzheimer’s and vascular dementia. Controlling blood pressure, cholesterol, and blood sugar can prevent further damage to the brain, and selective serotonin reuptake inhibitors (SSRIs) can be used to treat severe depression if lifestyle and social changes do not suffice. In certain cases, medications such as haloperidol or risperidone may help manage harmful behaviours, but they are not considered first-line treatments. 

Lifestyle adjustments also play a vital role in managing dementia. Staying physically active, engaging in cognitive and social activities, eating a balanced diet, avoiding smoking and alcohol, and keeping up hobbies can help preserve daily functioning. Planning ahead, including creating advance care plans and identifying trusted individuals to assist with decisions, is essential. For caregivers, the emotional and physical toll can be significant, making it important to seek support, take regular breaks, and practice stress management.

What does the new study tell us?

The JAMA Neurology study, titled “Ambient Air Pollution and the Severity of Alzheimer Disease Neuropathology,” analysed 602 brain autopsy cases collected between 1999 and 2022 at the Center for Neurodegenerative Disease Research Brain Bank at the University of Pennsylvania.

Researchers estimated each participant’s exposure to PM2.5 in the year prior to death or before their last Clinical Dementia Rating Sum of Boxes (CDR-SB) assessment—the sum score of six domains used to stage dementia severity. The study aimed to examine whether fine particulate pollution could not only increase dementia risk but also worsen disease severity through Alzheimer’s-related neuropathologic changes (ADNC). 

Results revealed a strong association between higher PM2.5 exposure and severe Alzheimer's disease neuropathology. Individuals exposed to elevated PM2.5 levels had a significantly greater likelihood of advanced ADNC. In a subset of 287 participants with clinical dementia records, higher pollution exposure corresponded with increased cognitive and functional impairment. The study also found that approximately 63 per cent of the link between PM2.5 exposure and cognitive decline was mediated by Alzheimer’s-related brain changes. 

The study highlights that PM2.5 exposure may directly affect the brain’s vulnerability to neurodegeneration. It was observed that higher PM2.5 levels were associated with more severe amyloid and tau pathologies, which are hallmarks of Alzheimer’s disease, ultimately culminating in advanced ADNC. Importantly, these associations were not influenced by the APOE ε4 allele, which is the strongest risk factor gene for Alzheimer's disease, indicating that the effects of air pollution apply across genetic predispositions. 

"This autopsy cohort study reinforces the finding that PM2.5 exposure appears to negatively affect cognitive function and suggests that this relationship may be mediated by ADNC. Our findings suggest that PM2.5 exposure may exacerbate AD pathogenesis," concludes the study which builds on prior population-based studies that showed a link between PM2.5 exposure and cognitive decline. This research provides detailed neuropathologic evidence, reinforcing the connection between environmental factors and Alzheimer’s disease progression. 

However, it also called for further population-based autopsy studies "to replicate our findings and better understand relationships among PM2.5 exposure, cognition, and neuropathology." 

While the study has notable strengths, including the use of a large autopsy series and robust sensitivity analyses, it also has limitations, as they point out themselves. “First, our clinical research-oriented autopsy cohort is skewed demographically. Indeed, the vast majority of subjects were white, non-Hispanic or Latino, highly educated with a higher than college degree, and/or from less disadvantaged neighbourhoods. This biased, unrepresentative sample may limit the generalizability of our findings,” it said, adding that their cohort may be subject to selection bias, as it included "a large proportion of cases through research programs that were enriched for AD dementia and that did not enroll individuals with vascular dementia."  

It is also pointed out that their sample size was small, PM2.5 exposure was measured only at the last residential address, and the study was not as longitudinal, and confounding factors such as lifestyle habits, smoking, alcohol use, and exposure to other pollutants were not fully evaluated.  

Nevertheless, the study provides compelling evidence that long-term exposure to fine particulate matter may exacerbate Alzheimer’s-related brain damage and cognitive decline. 

Why do the findings matter for India?

In India, the air quality crisis is severe. In 2024, India had an average AQI of 111 across the 12 months of the year, making it the country with the third most polluted air in the world, after Bangladesh and Pakistan. The average PM2.5 levels across the country was 48µg/m³, which is more than three times the WHO’s recommended safe limit of 15µg/m³. In fact, among the world's most polluted cities with the highest PM2.5 levels, the top seven positions were held by Indian cities, with Delhi topping the charts with an average PM 2.5 level of 95µg/m³—more than six times the recommended safe limits.  

Dr Pradeep Mahajan, Regenerative Medicine expert and Surgeon at StemRx Hospital & Research Centre, underlined that air pollution is emerging as a major factor in neurological health, particularly in relation to dementia and other degenerative brain diseases. While he acknowledged that multiple causes contribute to these conditions, he stressed that pollutants like PM2.5 play a decisive role when exposure is long-term. 

“We are in a phase where the basic aetiology of neurological diseases has expanded to include environmental factors like pollution,” Dr Mahajan explained. “Of the pollutants present in the air—whether carbon-based or fine particles like PM2.5—long-term exposure plays a role, 200 per cent.

The effect depends on how much exposure we get, how long it lasts, and what levels we are experiencing in metros. It may not be the only factor, but it is certainly a major one. Controlling it will have long-term benefits not only for dementia or degenerative conditions but for overall health.” 

However, he cautioned that India does not yet have enough dedicated research on this link. “There are certain global studies supporting the pollution-dementia connection. But in India, we’ve never studied pollution alone as an isolated factor. Here, dementia, Alzheimer’s, or Parkinson’s are usually the result of multiple factors—genetics, environment, and health history. Pollution, when added to these, increases susceptibility, and in some cases may even cause earlier onset of disease,” he said. 

According to Dr Mahajan, people with a family history of dementia, Parkinson’s, or psychiatric disorders, as well as those born after high-risk pregnancies or who suffered childhood neuroinflammation or developmental delays, are especially vulnerable. “In such families, the chances of early development are higher. On the other hand, families without this genetic or medical background may not experience the same degree of risk,” he noted. 

He emphasised that awareness is key. “Most people—including 99 per cent of practising clinicians—are not fully aware of the neurological impact of pollution,” Dr Mahajan pointed out. “We need to start with high-risk groups: identify them, educate them, and make them aware of their limitations and preventive measures.” 

While acknowledging that avoidance of pollution is difficult in India, he suggested practical precautions: intermittent changes of environment for those with long-term exposure, and the use of protective masks in high-concentration areas. For non-risk patients, he said, awareness and smaller interventions could still help. 

“Talking about prevention is easy in theory, but in practice it is very difficult in our context,” Dr Mahajan admitted. “Still, the first step is awareness—guiding people, especially sensitive groups, to understand the risks and to take precautions where possible.” 

This story is done in collaboration with First Check, which is the health journalism vertical of DataLEADS.

 

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