Car honks, sirens and other traffic noises may increase the risk of stroke, particularly for older individuals, according to a new study.
The study, which looked at the association between road traffic noise and stroke in more than 51,000 Danish people, found that for every 10-decibel increase in noise level, the risk of stroke increased by 14 percent. In those over 65, the risk of stroke increased 27 percent.
The increase in risk was most significant for noises louder than 60 decibels, about the loudness of normal conversations, the researchers said. (The decibel (dB) scale is logarithmic, so a 60-decibel noise is 10 times louder than a 50-decibel noise.)
The study adds to a growing body of research showing that exposure to traffic noise may pose cardiovascular risks, the researchers said. Previous studies have linked traffic noise with an increased risk of heart attacks and high blood pressure. The new study is the first to examine the connection between traffic noise and stroke.
The results held even after the researchers took into account other factors that might influence stroke risk, including age, gender, smoking status, physical activity, intake of vegetables, exposure to noise from railways and airports and exposure to air pollution.
The study highlights the need to reduce the public's exposure to traffic noise, said study researcher Mette Sørensen, of the Institute of Cancer Epidemiology in Copenhagen. However, the researchers noted the finding shows only an association, not a direct cause-effect link. Further studies will be needed to confirm traffic noise ass a contributor to stroke risk.
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Mette and her colleagues analyzed data from Danish citizens in Copenhagen and Aarhus who completed a lifestyle questionnaire between 1993 and 1997, and examined the participants' medical histories and residential addresses. Road traffic noise was estimated using a model that took into account traffic composition, speed, road surfaces and the heights of homes relative to the roads.
About 35 percent of the participants were exposed to traffic noise levels above 35 decibels. The noise level was estimated to range from about 40 to 80 decibels.
Over the course of the study, 1,881 participants suffered a stroke.
The researchers estimated that traffic noise could account for 8 percent of all stroke cases in the population, and 19 percent of cases in those aged 65 years and older, Sørensen said.
Why does noise increase stroke risk?
Exposure to noise is thought to increase blood pressure and cause changes in levels of stress hormones, which may contribute to the increased risk of stroke. In addition, exposure to traffic noise may also lead to sleep disturbances, which can contribute to stroke risk, Sørensen told MyHealthNewsDaily.
Older people are more susceptible to sleep disturbances, which could explain why the link was strongest for those 65 and over, Sørensen said.
The study is published today (Jan. 26) in the journal European Heart Journal.