Dirty air linked to increased dementia risk

Regular exposure to air pollution may greatly increase the risk of developing dementia, new research shows.

The London-based study, published in the journal BMJ Open, found that people living in areas with high levels of nitrogen oxide and PM2.5 - microscopic particles generated by fossil fuels - in the air were more likely to develop the neurodegenerative condition.

The scientists used estimates of air and noise pollution levels across the English capital and correlated these with the health records of 131,000 patients registered at 75 general practices within the M25 in 2004. All the patients were aged between 50 and 79, and had not been diagnosed with dementia.

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Their health was tracked for an average of seven years from 2005, during which a total of 2,181 of the patients - 1.7% - were diagnosed with dementia. Of this group, 39% had Alzheimer’s disease, while 29% had vascular dementia.

The researchers - from the University of London, Imperial College and King’s College London - said they cannot establish that air pollution was a direct cause of the dementia cases. However, the diagnoses “were found to be linked to ambient levels of nitrogen dioxide and PM2.5, based on estimates taken near the homes of patients in 2004”, says The Independent.

Those living in areas with the highest nitrogen dioxide levels had a 40% increased risk of being diagnosed with dementia compared with those living in areas with the lowest, the scientists found.

Study co-author Frank Kelly, a professor of environmental health at King’s College London, told The Guardian: “I believe that we now have sufficient knowledge to add air pollution to the list of risk factors for dementia.”

There are around 850,000 people with dementia in the UK, a figure that is expected to rise to a million by 2025.

Alzheimer’s Research UK told the London Evening Standard that the link between air pollution and dementia risk is a “growing area of research”, but said the results should be treated with caution.

The charity’s chief scientific officer, David Reynolds, said: “While the researchers tried to account for factors like wealth, heart disease and other potential explanations for differences in dementia rates across the capital, it is difficult to rule out other explanations for the findings.

“The diseases that cause dementia can begin in the brain up to 20 years before symptoms start to show. We don’t know where people in this study lived in the two decades before their dementia diagnosis, so we have to be cautious about how we interpret these results.”