An anonymous reader quotes a report from The Guardian: People living near a busy road have an increased risk of dementia, according to research that adds to concerns about the impact of air pollution on human health. Roughly one in 10 cases of Alzheimer's in urban areas could be associated with living amid heavy traffic, the study estimated -- although the research stopped short of showing that exposure to exhaust fumes causes neurodegeneration. Previously, scientists have linked air pollution and traffic noise to reduced density of white matter (the brain's connective tissue) and lower cognition. A recent study suggested that magnetic nano-particles from air pollution can make their way into brain tissue. The latest study, published in The Lancet, found that those who live closest to major traffic arteries were up to 12% more likely to be diagnosed with dementia -- a small but significant increase in risk. The study, which tracked roughly 6.6 million people for more than a decade, could not determine whether pollution is directly harmful to the brain. The increased dementia risk could also be a knock-on effect of respiratory and cardiac problems caused by traffic fumes or due to other unhealthy life-style factors associated with living in built-up urban environments. The study tracked all adults aged between 20 and 85 living in Ontario, Canada from 2001 to 2012, using postcodes to determine a person's proximity to major roads. The cohort's medical records were examined to see who went on to develop dementia, Parkinson's disease or multiple sclerosis. Over the study period, more than 243,000 people developed dementia, 31,500 people developed Parkinson's disease and 9,250 people developed multiple sclerosis. The scientists found no link between living near a road and Parkinson's disease or multiple sclerosis, but dementia was slightly more common in people living close to busy roads and the risk dropped off gradually in less built-up areas. Those living within 50 meters of a busy road had a 7% higher risk in developing dementia, the risk was 4% higher risk at 50-100 meters, 2% higher risk at 101-200 meters and there was no increase in risk in those living more than 200 meters away. Those who lived in a major city, within 50 meters of a major road and who did not move house for the duration of the study had the highest risk at 12%.