Inside the orbital? Air pollution linked to Alzheimer’s within the M25

Researchers uncover a correlation between exposure to air pollutants and an increased risk of developing Alzheimer’s in a London-based study.

Recent research involving several London-based universities and led by first author Ian Carey (University of London; UK) has established a correlation between increased exposure to air pollutants and a risk of developing Alzheimer’s. The study, which originally set out to identify if dementia occurrence was linked to air and noise pollution, identified the correlation but is yet to establish a causal link.

Using information from the Clinical Practice Data Link for 75 practices within the London orbital motorway, the researchers focused on almost 131,000 patients who, in 2004, were between the ages of 50-79 and had not been diagnosed with dementia. Using calculated estimates of air pollutants, the team established the yearly exposure of each subject to NO₂, PM_2.5 and O_3.  The subjects were monitored for 7 years on average, until they were diagnosed with dementia, left the practice, or died.

The study found that 1.7% (2181) of all subjects developed dementia and that on first inspection, there was a correlation between air pollutants and dementia risk, with those living in regions with the top fifth of NO₂ pollution running a 40% higher risk of developing dementia than those in the bottom fifth, with similar results for PM_2.5 pollution.

Closer examination revealed that the correlation was only present in the specific form of dementia; Alzheimer’s, while other specific types of dementia did not express an association with air pollutants. While the study is unable to establish a causal link, this information could prove useful in identifying the pathogenesis between the disorder and pollution.

There is clear scope for further research to be conducted in order to establish the mechanisms by which air pollutants may precipitate Alzheimer’s. “Traffic related air pollution has been linked to poorer cognitive development in young children, and continued significant exposure may produce neuro-inflammation and altered brain innate immune responses in early adulthood,” the team postulated. The significance of this study to public health and policy could be far-reaching with Alzheimer’s being a progressively prevalent disease in our society and an increasing burden on the NHS.