About 10 percent of dementia cases in people living within 50m of a major road could be down to traffic, the study suggests. With distance from the road, the risk dissipated until, 200 meters away from a major road, residents were at no more risk than those who lived further away.
But now scientists tracking 6.6 million people living in the Canadian province of Ontario have found up to one in 10 cases of dementia among those living 50 metres from a busy road could be attributed to their exposure to high levels of traffic. "Our study suggests that busy roads could be a source of environmental stressors that could give rise to the onset of dementia". Ray Copes, chief of environmental and occupational health at Public Health Ontario, said Wednesday. They used postcodes to determine how close people lived to a road and analysed medical records to see if they went on to develop dementia, Parkinson's disease or multiple sclerosis.
Tracking these people over a period of 11 years found a clear link between dementia incidence and living near a main road, comparable to the M1 or M4 in the United Kingdom, or major state or interstate highways in the US. To be included in the study, subjects had to be free of any neurological disease.
However, the study looks only at where people diagnosed with dementia live.
Nearly everyone (95 percent of the participants) in the study lived within 1 kilometer of a major road.
"Regardless of the specific nature of air pollutants, people living close to busy roads will inhale large amounts of complex mixtures of pollutants, and every individual will respond differently to the same air pollutants", Lilian Calderón-Garcidueñas and Rodolfo Villarreal-Ríos, medics at the University of Montana, wrote in a comment article in The Lancet. "With our widespread exposure to traffic and the greater tendency for people to live in cities these days, this has serious public health implications".
The incurable condition is a leading cause of disability and dependency, and is starting to overtake heart disease as a cause of death in some developed countries. Scientists are still pinpointing exactly how air pollution changes the brain, but as Reuben noted, fine particulate matter found in vehicle exhaust is small enough to travel throughout our bodies-including to our brains. However, it found no link between traffic exposure and Parkinson's disease or multiple sclerosis.
Dr. Morris Freedman, head of neurology at Baycrest Health Sciences in Toronto, called the study "very interesting".
"Undoubtedly living in conditions of severe air pollution is extremely unpleasant and it is hard to suppose that it is good for anyone".
"The answer is not so clear". Other causes of dementia include stroke and hypertension.
The potentially damaging effect of air pollution and noise from heavy traffic on the brain has been the subject of a number of studies. "We must implement preventive measures now, rather than take reactive actions decades from now".
"We know that major road air pollution is bad for general health and this latest study doesn't tell us whether the small increase in dementia risk is driven by indirect effects or whether proximity to traffic directly influences dementia pathology".
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