Scientists have warned there are growing links between air pollution and an increased risk of dementia.
The team from the University of Cambridge undertook an analysis of studies incorporating data from almost 30 million people which has highlighted the role that air pollution – including that coming from car exhaust emissions – plays in increased risk of dementia.
Dementias such as Alzheimer’s disease are estimated to affect more than 57.4 million people worldwide, a number that is expected to almost triple to 152.8 million cases by 2050. The impacts on the individuals, families and caregivers and society at large are immense.
While there are some indications that the prevalence of dementia is decreasing in Europe and North America, suggesting that it may be possible to reduce the risk of the disease at a population level, elsewhere the picture is less promising.
Air pollution has recently been identified as a risk factor for dementia, with several studies pointing the finger at a number of pollutants. However, the strength of evidence and ability to determine a causal effect has been varied.
In a paper a team led by researchers at the Medical Research Council (MRC) Epidemiology Unit, University of Cambridge, carried out a systematic review and meta-analysis of existing scientific literature to examine this link further. This approach allowed them to bring together studies that on their own may not provide sufficient evidence, and which sometimes disagree with each other, to provide more robust overarching conclusions.
In total, the researchers included 51 studies, including data from more than 29 million participants who had been exposed to air pollutants for at least one year, mostly from high-income countries. Of these, 34 papers were included in the meta-analysis: 15 originated in North America, 10 in Europe, seven in Asia, and two in Australia.
Senior author Dr Haneen Khreis from the MRC Epidemiology Unit said: “Epidemiological evidence plays a crucial role in allowing us to determine whether or not air pollution increases the risk of dementia and by how much. Our work 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.
“Tackling air pollution can deliver long-term health, social, climate, and economic benefits. It can reduce the immense burden on patients, families, and caregivers, while easing pressure on overstretched healthcare systems.”
The researchers found a positive and statistically significant association between three types of air pollutant and dementia. These were:
