Jan. 25, 2011 -- The noises generated by road traffic may increase the risk of stroke, especially in older people, new research indicates.
In a new study, which its authors say is the first to investigate links between road traffic noise and stroke risk, researchers found that for every 10 decibel increase in noise, the risk of having a stroke increased 14% overall in a participant pool of 51,485 people.
Danish scientists say they found no statistically significant increased risk of stroke caused by road noise in people under 65.
The risk, however, increased by 27% for every 10 decibels of higher road traffic noise in people aged 65 and older.
What’s more, the researchers say in a news release that they found indications of a threshold limit of about 60 decibels, above which the risk of stroke seemed to increase even more.
Traffic Noise and Cardiovascular Disease
"Our study shows that exposure to road traffic noise seems to increase the risk of stroke," says study author Mette Sorensen, senior researcher at the Institute of Cancer Epidemiology at the Danish Cancer Society in Copenhagen. "Previous studies have linked traffic noise with raised blood pressure and heart attacks, and our study adds to the accumulating evidence that traffic noise may cause a range of cardiovascular diseases."
She says that such findings highlight "the need for action to reduce people's exposure to noise" and that more research is needed before firm conclusions can be made about the apparent links between noise and cardiovascular events. This study shows an association, but cannot prove cause and effect.
The study involved 57,053 people aged 50 to 64 in high traffic areas of Copenhagen and Aarhus, Denmark’s second largest city, between 1993 and 1997.
The researchers say medical and residential histories were available for 51,485 of the participants, and that their average follow-up time was 10 years. During that period, 1,881 had a stroke.
Other Possible Stroke Causes Were Factored Out Before Conclusion Reached
Sorensen and colleagues say they made allowances in the study for the effects of air pollution and exposure to other sources of noise, such as that from railroads and airplanes. They also took into consideration lifestyle factors such as smoking, alcohol and caffeine use, and diet.
The data on where the study participants lived was linked to a noise calculation program that has been used to map noise levels in a number of locations in Scandinavia for several years. This program takes into account the amount of traffic congestion and speed, the type of road, such as rural or high-speed freeway, types of road surfaces, and the heights of people’s homes compared to the road surfaces.
At the start of the study, 35% of the people were exposed to noise levels greater than 60 decibels, and 72% lived at the same address through the end of the research project. The researchers’ lowest estimate for noise exposure was 40 decibels, and the highest was 82 decibels.
To put this into context, a jackhammer produces about 130 decibels and a jet plane taking off about 120.
Reasons for Link Between Noise and Stroke Are Not Clear
Sorensen says that though the mechanisms that would link noise to stroke remain undetermined, they likely are the same ones that are involved in the link of noise with hypertension and heart attacks.
The noise acts “as a stressor and disturbs sleep, which results in increased blood pressure and heart rate, as well as increased level of stress hormones,” she says. “Taken together, all of these could increase the risk for cardiovascular diseases.”
She says older people have more “fragmented sleep patterns” and are thus more susceptible to sleep disturbances, and that this fact could explain the apparent correlation between road noise and increased stroke risk in this age group.
“This is the first study on the association between transport noise and risk for stroke, as previous studies on transport noise focused mainly on hypertension and ischemic heart disease,” the authors write.
The study is published Jan. 26 in the European Heart Journal.