Dementia: Living Near Major Roads Linked To Increased Risk Of Memory Loss

People living near major roadways have an increased risk of dementia, according to a new study published in the journal Lancet. However, the study stopped short of establishing causality between living near the roads and incidences of dementia.

"Increasing population growth and urbanization has placed many people close to heavy traffic, and with widespread exposure to traffic and growing rates of dementia, even a modest effect from near-road exposure could pose a large public health burden," study lead author Hong Chen, from Public Health Ontario, Canada, said in a statement. "More research to understand this link is needed, particularly into the effects of different aspects of traffic, such as air pollutants and noise."

For the purpose of the study, the researchers tracked all adults between 20 and 85 years living in Ontario — roughly 6.6 million people — for over a decade, from 2001 to 2012. They used postcodes to ascertain the residents' proximity to major roads — determined based on traffic volume — and found that 95 percent lived within 1 km (0.62 miles) of a major road.

The researchers then analyzed medical records to see how many of the 6.6 million went on to develop dementia, Parkinson's disease or multiple sclerosis.

A total of 243,611 cases of dementia were diagnosed during this period. Over 31,500 people developed Parkinson's disease and nearly 9,250 people developed multiple sclerosis.

Adjusting for individual and societal factors such as diabetes, brain injury, poverty and education levels, the researchers found that the risk of developing dementia reduced as people lived further away from a main road. Compared to those living 300 meters away from a major road, the risk of developing dementia was 7 percent higher in those living within 50 meters, 4 percent higher at 50-100 meters, and 2 percent higher at 101-200 meters.

The researchers did not find any association between living near a road and Parkinson's disease or multiple sclerosis.

It should be noted that the study does not state that living near a major road is the cause of an increased risk of dementia, and neither is it possible to infer cause and effect relationship from it. For instance, it may just be possible that those living in less accessible areas located farther away from major roads are less likely to consult a doctor, and thus are less likely to be diagnosed with dementia.

However, previous studies have linked air pollution and traffic noise — both of which people living near roads would be exposed to more than those living farther away — to reduced white matter density and lower cognition.

"Research to date suggests that the best way to reduce your dementia risk is to look after your general health – stop smoking, control your blood pressure and blood sugar level and take exercise," Rob Howard, a professor of old age psychiatry at University College London, who was not involved in the study, told the Guardian. "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. Regardless of the route of causation, this study presents one more important reason why we must clean up the air in our cities."