Exposure to certain air pollutants significantly raises the risk of developing dementia, according to the most comprehensive study of its kind by Cambridge University researchers. The study, published by the Medical Research Council's epidemiology unit, reviewed 51 studies involving over 29 million participants exposed to pollutants for at least a year.
The research found a positive and statistically significant association between three types of air pollutant and dementia: PM2.5 from vehicle emissions, power plants, and woodburning stoves; nitrogen dioxide from burning fossil fuels; and soot from vehicle exhaust and wood burning. For every 10 micrograms per cubic metre increase in PM2.5, the relative risk of dementia rose by 17%, while for soot the increase was 13%.
In 2023, PM2.5 and soot levels approached or exceeded these thresholds at roadside locations in central London, Birmingham, and Glasgow. Dementia currently affects about 57 million people worldwide, with numbers expected to rise to at least 150 million by 2050. In the UK, around 982,000 people have the condition, most commonly Alzheimer's disease.
Dr Haneen Khreis, senior author, said the study provides 'further evidence to support the observation that long-term exposure to outdoor air pollution is a risk factor for the onset of dementia in previously healthy adults.' She added that tackling air pollution could deliver health, social, climate, and economic benefits, reducing the burden on patients and healthcare systems.
The researchers noted limitations, as most studies included white participants from high-income countries, and called for future research to include more marginalised groups. Dr Isolde Radford of Alzheimer's Research UK said the review 'adds to mounting evidence that exposure to air pollution increases the risk of developing dementia' and urged government action, stating that 'air pollution is one of the major modifiable risk factors for dementia – but it's not something individuals can solve alone.'
