Living in a polluted area increases the risk of dementia by up to 40 per cent, a new study has suggested, in a year where the legal air pollution limits were reached in London within one month.
Researchers say that thousands of cases of the illness each year could be preventable by cutting traffic fumes. Air pollution has already been linked with cardiovascular and respiratory disease, but this is one of the first studies to examine links with neurodegenerative illnesses like dementia.
Data from more than 130,000 patients at London GP practices was used in the study.
The anonymised health of each patient used for the study was tracked for an average of seven years. Between 2005 and 2013, about 2,200 of these patients were diagnosed with dementia.
The observational study, published in the BMJ Open journal on Wednesday, cannot establish that air pollution was a direct cause of the dementia cases.
The King’s College London study adds to a growing body of research that shows air pollution can affect the brain.
However, the authors warned that the results must be taken cautiously because the study could not track other possible causes.
This includes lifestyle factors or relative economic deprivation of the patients studied.
The amount of air pollution each respondent was subject to could also not be measured accurately. Last year a Canadian study of 2.2 million people concluded that those who lived continuously near a busy road were 12 per cent more likely to get dementia.
Frank Kelly, of King’s College London, senior author of the study, said that while the results were not conclusive “it is increasingly appreciated that the impacts of air pollution on health are seen far beyond the lungs”.
Kelly added: “Air pollution is linked with many more conditions than dementia and therefore there is now overwhelming evidence that we should be improving air quality in cities to improve public health.”
Traffic fumes, particularly from diesel, are the main sources of PM2.5 and NO2.
Ministers have a responsibility to cut pollution, Kelly said. He advised people wanting to minimise their exposure to pollution by planning “low pollution” routes and by trying to avoid rush hour traffic when air pollution peaks.
James Pickett, of the Alzheimer’s Society, said this evidence linking dementia and brain functions is still unclear and that “more robust research into how pollution affects brain health” is required.
The paper’s authors said a link between poor air quality and dementia could begin early in life.
They wrote: “Traffic related air pollution has been [linked to] poorer cognitive development in young children, and continued significant exposure may produce neuroinflammation and altered brain innate immune responses in early adulthood.”
They added: “The cause of these neurodegenerative diseases is still largely unknown… while toxicants from air pollution have several plausible pathways to reach the brain, how and when they may influence neurodegeneration remains speculative.”
Earlier this year the government warned two councils of “serious consequences” after they failed to meet the deadline for dealing with air pollution.
The Labour Party, local councils and environmental groups all responded by blaming the government – and Environment Secretary Michael Gove – for withholding the necessary resources and compelling legislation.
A recent NO2 (nitrogen dioxide) study named Marylebone Road and Hyde Park Corner in Central London as the most polluted postcodes in all of Britain.
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