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Traffic noise raises risk of stroke

1st February 2011

People age 65 and over should stay as far away from loud traffic noise as they can, to lower their risk of stroke, according to a recent Danish study.

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The researchers found that increasing the amount of road noise to which people were exposed by just 10 decibels was enough to bring a 27% increased statistical likelihood of stroke, in people 65 and over.

The researchers also found that noise levels over 60 decibels caused an even higher stroke risk, in people 65 and over.

In Denmark, people suffer 12,400 new cases of stroke every year, and 1,881 people suffered a stroke during the 10-year study period.

At the time when the study began, about 35% of the study subjects lived in areas where noise levels were routinely greater than 60 decibels.

The lowest noise exposure was about 40 decibels, and the highest hovered around 80.

By comparison, the human threshold of hearing is 0 decibels, the sound of someone breathing is about 10 decibels, and the sound of a quiet room is about 20 decibels.

Study author Mette Sorensen, senior researcher at the Institute of Cancer Epidemiology of Danish Cancer Society in Copenhagen, said that although her team's study was the first study on traffic noise and stroke, the results did not surprise her.

She said that earlier studies had found a strong link between cardiovascular diseases and traffic noise.

For the study, the researchers followed about 57,000 people.

Using computers, the researchers created a 'noise map' of the areas where people lived.

All of the people recruited for the study lived near the cities of Aarhaus or Copenhagen.

The baseline for the statistical calculations was the noise level of an average conversation.

Like any study that uses statistical methods, the recent study does not actually posit a causal link between road noise and stroke.

Despite the limitations of statistics, however, the researchers were able to come up with several guesses as to why road noise may increase people's risk of stroke.

Increased road noise may cause people to have disturbed sleep, which can be a factor.

The researchers said that, since the data for the study originated in cities, further research would be needed to provide a more balanced view.

Sorensen said that some 600 new cases of stroke were bound to pop up every year in connection with road noise.

She said that levels of stress hormones, increased heart rate and blood pressure, and an impaired immune system were likely factors in the correlation.

Larry B. Goldstein, director of the Duke Stroke Centre at Duke University in North Carolina in the US, said he believed that the study did a reasonable job of protecting the statistical relevance of its data.

He said that it was difficult to fully protect statistical calculations from some form of bias, however.

The researchers said that the people who were exposed to noise louder than 60 decibels also happened to have lower incomes than those who lived in quieter areas of Copenhagen and Aarhaus.

Sorensen said her study could be used as a basis for new construction materials that did a better job of absorbing sound and dampening noise.


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