Dementia is a growing global health challenge, with over 55 million people living with dementia worldwide and numbers expected to rise sharply in the coming decades. Because there is still no cure, prevention and risk reduction are at the forefront of research efforts. To make real progress, we must better understand what increases the risk of dementia, and crucially, which factors we might be able to change.
Now, imagine if the very air we breathe could be speeding this process along? That’s the unsettling possibility raised by a growing body of research linking air pollution to changes in how our brains age.
Air pollution is already a well-known culprit in heart and lung disease, but more recently researchers have turned their attention to its impact on brain aging and dementia. Previous studies have shown associations between higher exposure to pollutants and increased risk of dementia.
Indeed, the Lancet Commission on dementia prevention, intervention and care concluded that later life air pollution is one of 14 potentially modifiable risk factors for dementia, estimating that if we can eradicate air pollution, we may be able to reduce the number of dementia cases worldwide by 3% (Livingston et al., 2024) . Therefore, pollution doesn’t just affect our bodies; it may also impact brain health and the likelihood of someone developing dementia.
A new analysis of the 1946 British Birth Cohort datasets takes this further by examining how air pollution exposure in midlife affects memory, thinking skills, and even brain structure later in life (Canning et al, 2025).
Could those midlife years spent commuting through traffic fumes or living near busy roads be leaving lasting footprints on the ageing brain?
Methods
This study used data from 5,362 people born in the UK in 1946 who participated in the British Birth Cohort study, a long-term study following their health and brain development throughout their lives.
Researchers estimated participants’ exposure to air pollution at different ages, using NO2, PM10, Nox, PM2,5, PMcarse, and PM2.5abs which are all particles and gases in the air mostly from traffic, industry and burning fuel. Researchers also assessed cognitive ability including verbal memory, processing speed, verbal fluency and a general measure of cognitive ability using the standardised Addenbrookes Cognitive Examination-III (ACE-III)).
A small number of participants also underwent magnetic resonance (MRI) brain imaging aged 69-71, to calculate the volume of different parts of the brain (full brain, right hippocampus, and ventricular volume).
Results
The findings were somewhat mixed, and various subset analyses were carried out.
In a sample of 1,761 people:
- Overall, air pollution exposure was not linked to decline in verbal memory between the ages of 43 to 69 years old.
- However, higher exposure to specific pollutants (NO2 and PM10) was associated with slower processing speed over the same age range.
- Further, higher exposure to all types of pollution was associated with lower ACE-III scores at 69-71.
- Importantly this relationship was maintained even when controlling for a number of variables such as biological sex, father’s social class, educational attainment, neighbourhood deprivation, socioeconomic status as an adult, and childhood/adolescent exposure to air pollution.
When examining brain volume through neuroimaging in a subsample of 453 people:
- Higher exposure to some pollutants, in particular Nox, was associated with smaller hippocampus volumes, the part of the brain important for memory and learning, aged 69-71.
- Higher exposure to NO2 and PM10 was associated with larger ventricular volume, which can indicate loss of brain tissue or brain shrinkage, aged 69-71.
- None of the air pollutants studied were associated with total brain volume.
- Again, this relationship was maintained even when controlling for: biological sex, fathers social class, educational attainment, neighbourhood deprivation, socioeconomic status as an adult, childhood/adolescent exposure to air pollution, and age at which the scan occurred.
Even when controlling for multiple factors, pollutants such as NO2 and Nox contributed to functional cognitive decline and brain changes associated with tissue and memory damage.
Conclusions
The authors concluded that their study suggests that exposure to polluted air, from midlife to older age, has a potentially detrimental effect on brain health.
In particular, people exposed to high levels of nitrogen dioxide, other nitrogen-based pollutants, and larger airborne particles tended to have cognitive and structural neurological features associated with slower thinking skills, poorer overall cognition and changes in their brain structure.
This study’s findings are in line with a broad body of prior evidence: air pollution exposure can be related to a lasting negative effect on brain structure & function in old age.
Strengths and limitations
This study undeniably has several strengths. It followed a large, population-based group of people from birth into older age, giving a rare long-term view of how exposure to pollution may affect our brains. The researchers gathered detailed estimates of different types of air pollution and cognitive abilities allowing for detailed and comprehensive analyses to be conducted. A particular strength is the inclusion of brain scanning, enabling direct evaluation of the effects of pollutant exposure on brain structure. This allows the study to expand upon current evidence, making a novel contribution to the current literature.
Finally, analyses were carefully adjusted for important factors such as sex, education, socioeconomic status, and early-life exposures, strengthening the reliability of the findings. It would be of interest to learn how they controlled for childhood/adolescent exposure to air pollution, as this may have a longitudinal, cumulative and confounding effect on cognitive functional and structural brain changes, which are difficult to disentangle from adult pollution exposure.
However, limitations may weaken the reliability of the findings. As the authors noted themselves, they elected not to control for the multiple comparisons they conducted. In this study the authors conducted 36 different comparisons, this means there is an 84% chance of getting at least one false positive (observing a positive finding by chance). Therefore, we should treat the findings with caution.
Another limitation relates to the “healthy cohort effect”. The healthy cohort effect is a type of selection bias that occurs in long-term study, and it refers to the fact that people who remain in longitudinal studies over a long period of time tend to be healthier, more motivated, or have better lifestyles than those who elect not to participate at all or who drop out. This can make study results look more compelling than they really are, because the sample no longer represents the full range of health outcomes in the original population, limiting its utility as a population-based study, especially in the absence of a dropout analysis. In this specific study, 15% of ACE-III results were missing at age 69, but it is not clear what caused the ‘missingness’ of functional cognitive data, and without a dropout analysis the utility of the data itself to derive causal links is limited.
There was a 5-year gap between the final exposure measurement (age 60-64) and outcome measurement (age 69-71). The researchers have assumed that, even if the people remained resident in the same areas over the prior 5 years, their pollutant exposure in this time remains stable. This may not be the case, especially if the participant resides in an urban location or relocates from an urban to rural locality, or their locality experiences significant pollutant emission from e.g. local construction during this time period.
Furthermore, while the authors only appear to consider the impact of outdoor air pollutant exposure, this study does not evaluate or account for the potential impact of indoor and occupational pollutant exposure on neuropsychiatric health outcomes. A 2014 study found that long term exposure to carbon monoxide, which is more commonly associated with indoor spaces than outdoor spaces, is associated with increased risk of dementia (Chang et al., 2014). It may have been that certain participants in this study had greater exposure to these indoor pollutants, like carbon monoxide, than others, which will in turn impact the findings.
It is hard to exclude the impact of other factors, such as childhood pollutant exposure, which could contribute to the old age brain changes seen in this study.
Implications for practice
For individuals, these findings highlight the value of taking steps to reduce personal exposure to air pollution. Choosing walking or cycling routes away from busy roads, using public transport or vehicles with cleaner emissions, and limiting time spent in high-traffic areas, can all make small differences to lifetime pollutant exposure.
While much is made of carbon-compound pollutants, ‘smoke’ and respiratory and physical health, it is essential to increase psychoeducation on activities or situations that risk higher exposure to nitrogen-compound pollutants and their effect on brain structure and cognitive functioning.
Although not a direct focus of this study, wider implications may suggest that at home, improving indoor air quality through proper ventilation, using air purifiers, and maintaining fuel-burning appliances may not only support respiratory, heart and mental wellbeing, but may also promote healthy brain aging. Any gradual consistent actions may help reduce exposure over time, potentially reducing cognitive decline in later life.
For policymakers, urban planners, and public health professionals, the study reinforces the need to prioritise air quality in urban design and transport planning. Reducing traffic congestion, promoting green spaces, supporting cleaner public transport, and monitoring local pollution levels are all strategies that may help protect the cognitive health of local communities.
Taking a step back and looking at the bigger picture, these findings suggest that promoting brain health may require a broader perspective on health that goes beyond diet, exercise, and mental activity. That is, reducing air pollution through individual choices, urban planning, and public policy could play a critical role in reducing the risk of cognitive decline and dementia in ageing populations.
While reducing air pollution remains a serious challenge, even small steps could potentially prevent thousands of cases of cognitive decline in older age.
References
Primary paper
Canning T, Arias-de la Torre J, Fisher HL, Gulliver J, Hansell AL, Hardy R, Hatch SL, Mudway IS, Ronaldson A, Cartlidge M, James SN, Keuss SE, Schott JM, Richards M, Bakolis I. Associations between life course exposure to ambient air pollution with cognition and later-life brain structure: a population-based study of the 1946 British Birth Cohort (PDF). Lancet Healthy Longev. 2025 Jul;6(7):100724. doi: 10.1016/j.lanhl.2025.100724. Epub 2025 Jul 17. PMID: 40684776.
Other references
Livingston G, Huntley J, Liu KY, Costafreda SG, Selbæk G, Alladi S, Ames D, Banerjee S, Burns A, Brayne C, Fox NC. Dementia prevention, intervention, and care: 2024 report of the Lancet standing Commission. The Lancet. 2024 Aug 10;404(10452):572-628.
Chang KH, Chang MY, Muo CH, Wu TN, Chen CY, Kao CH. Increased risk of dementia in patients exposed to nitrogen dioxide and carbon monoxide: a population-based retrospective cohort study. PloS ONE. 2014 Aug 12;9(8):e103078.