Living near congested roads with high levels of air pollution can cause ‘ silent strokes ’ which increase the risk of dementia , scientists have warned . Exposure to small , sooty particles , mostly caused by traffic fumes and factory emissions , alters the structure of the brain , they said . The microscopic particles have previously been shown to cause lung damage and harmful changes in blood vessels and clotting , and are thought to contribute to the deaths of 29,000 people every year in Britain . Living near a congested road can increase the chance of developing dementia , research has found . Researchers examined the brains of more than 900 people aged more than 60 and assessed the pollution risk . US researchers found evidence that living near congested roads or polluted areas can lead to ‘ silent strokes ’ which in turn cause shrinkage of the brain and other damage . Silent strokes , which arise from blockages in blood vessels supplying the brain , do not have any outward symptoms and the victim is usually unaware of them . Sudha Seshadri , a professor of neurology at Boston University School of Medicine , said : ‘ This is concerning , since we know that silent strokes increase the risk of overt strokes and of developing dementia , walking problems and depression . ‘ We now plan to look more at the impact of air pollution over a longer period , its effect on brain shrinkage over time , and other risks including stroke and dementia. ’ The study , by Beth Israel Deaconess Medical Center and Boston University School of Medicine , involved more than 900 people aged 60 and over who did not have dementia or a history of strokes . It recorded how far participants lived from major roads and used satellite imagery to assess their exposure to the fine particulate matter known as PM2.5 . This is made up of small particles measuring just 2.5 micrometres , or 30 times smaller than the thickness of a human hair . These particles are generated from a variety of sources , including power plants , factories , trucks and cars and the burning of wood . They can travel deeply into the lungs and have been associated with increased numbers of hospital admissions for heart attacks and strokes . The study participants ’ brain matter was measured using MRI scans . The researchers found that increases in PM2.5 in towns and cities was linked with a 46 per cent higher risk of silent strokes . The research was published in a report in the journal Stroke . Researcher Elissa Wilker , of the Cardiovascular Epidemiology Research Unit at Beth Israel Deaconess Medical Center , said : ‘ This is one of the first studies to look at the relationship between ambient air pollution and brain structure . ‘ Our findings suggest that air pollution is associated with insidious effects , even in dementia and stroke-free individuals . ‘ The mechanisms remain unclear , but inflammation resulting from the deposit of fine particles in the lungs is likely important. ’ The study will add to mounting pressure on the Government , which faces a judgment at the Supreme Court next week over its failure to meet EU legal limits for air pollution . Sixteen cities – including London , Manchester , Glasgow , Sheffield and Birmingham – have failed to hit air quality targets .
American researchers examined more than 900 people aged 60 and over . Experts believe that air pollution could increase the risk of 'silent strokes ' Microscopic particles in pollution are thought to kill 29,000 people every year . The risk of having a silent stroke can be raised by more than 40 per cent .