January 25th, 2011
07:15 PM ET
Many people who live in cities or near highways are accustomed to a lullaby of cars whizzing by, but that noise may put them at increased risk of stroke, a new study suggests.
Research from Denmark, published in the European Heart Journal, found an association between exposure to residential road traffic and higher stroke risk among people older than age 64 1/2.
The findings should be interpreted with caution, however, because the researchers did not prove a causal connection between the sounds of traffic and stroke risk, said Dr. Keith Siller, medical director for the Comprehensive Stroke Care Center at NYU Langone Medical Center in New York, who was not involved in the study.
Participants included more than 57,000 people from Denmark, 1,881 of whom had a first-ever stroke between 1993 and 2006. Researchers constructed a noise level model from the history of residential addresses of participants. It appears that, adjusting for air pollution and other potential factors, people over 64 1/2 years old have a higher likelihood of stroke if they also had an average exposure of higher than 60 dB, which is the noise level of normal conversation. Above that number, the higher the volume, the higher the stroke risk.
It is possible that the stress of traffic noise raises blood pressure, which is a huge risk factor for stroke, Siller said.
Alternatively, it could be that there are other components of urban living that raise stroke risk, such as the stress of commuting and not having as much free time, Siller said.
That the risk was highest in older adults may relate to the hearing problems that tend to occur more often in the elderly, he said. In fact, some people in old age have difficulty hearing when there are multiple sound sources at once, such as in a crowded room; thus, traffic noise could cause disorientation, he said.
The authors posit that sleep disturbances due to traffic noise may also contribute to stroke risk. But Siller isn't so sure - there are people so accustomed to the hum of cars that they have more trouble sleeping in total silence.
Another factor at play may be socioeconomic status. Study authors noted that many of the people in the study with high levels of loud traffic noise exposure had low income, and socioeconomic status has been shown in the past to predict stroke risk. That's because lower income people may have fewer resources to deal with other stroke risk factors such as diabetes, and a less substantial social network of support.
Bottom line: Further research is needed to confirm the influence of traffic noise on stroke risk.
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