Long-term exposure to outdoor air pollution linked to increased risk of dementia

Summary

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 published in The Lancet Planetary Health, 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. The researchers found a positive and statistically-significant association between 3 types of air pollutant and dementia. These were: Particulate matter with a diameter of 2.5 microns or less (PM2.5), a pollutant made up of tiny particles small enough that they can be inhaled deep into the lungs. These particles come from several sources, including vehicle emissions, power plants, industrial processes, wood burning stoves and fireplaces, a...