Air pollution may be related to a heightened risk of developing dementia, according to research carried out by St George’s and King’s College London.


Air pollution is an established risk factor for heart disease/stroke and respiratory disease, but its potential role in neurodegenerative diseases, such as dementia, isn’t as clear.
The researchers used carefully calculated estimates of air and noise pollution across Greater London to assess potential links with new dementia diagnoses.
They looked at patient data on 131,000 Londoners aged 50 to 79, and based on their residential postcodes, the researchers estimated their yearly exposure to air pollutants. These were specifically nitrogen dioxide, fine particulate matter and ozone, as well as proximity to heavy traffic and road noise, using modelling methods validated with recorded measurements.
The health of the Londoners was then tracked over an average of 7 years. During the monitoring period, 2181 patients (1.7%) were newly diagnosed with dementia, including Alzheimer’s disease.
These new diagnoses were then examined with regard to concentrations of nitrogen dioxide and fine particulate matter estimated at the patients’ homes at the start of the monitoring period in 2004.
Those living in areas in the top fifth of nitrogen dioxide concentrations ran a 40% heightened risk of being diagnosed with dementia than those living in the bottom fifth. A similar increase in risk was observed for higher particulate matter levels.
These associations were consistent and unexplained by known influential factors, such as smoking and diabetes, although when restricted to specific types of dementia, they remained only for patients with Alzheimer’s disease.
This is an observational study, and as such, can’t establish cause, and the findings may be applicable only to London. Nor were the researchers able to glean longer term exposures, which may be relevant as Alzheimer’s disease may take many years to develop.
Many factors may be involved in the development of dementia, the researchers point out, the exact cause of which is still not known, and while there are several plausible pathways for air pollutants to reach the brain, how they might contribute to neurodegeneration isn’t clear.
But Dr Iain Carey, Senior Lecturer in Epidemiology at St George’s, said; “While these findings need to be treated with caution, they do replicate results from other recent international studies which have suggested a link between exposure to air pollution and dementia. More research is now needed to investigate whether curbing exposure to pollution might be able to delay the progression of dementia.”

The full research paper "Are noise and air pollution related to the incidence of dementia? A cohort study in London, England" was published in BMJ Open.