People living in environments with high levels of road traffic noise might be more likely to suffer myocardial infarction than people in quieter areas, according to a new study from Karolinska Institutet, Stockholm, Sweden, conducted in the Stockholm area.

The study compared 1,571 people from Stockholm County who had suffered a myocardial infarction between 1992 and 1994 with controls from the same area. In order to ascertain whether traffic noise in residential areas increases the risk of myocardial infarction, the addresses of all individuals during the past 20 years were identified, and a level of noise estimated. Similarly, exposure to air pollution was charted and information on different risk factors for myocardial infarction was gathered using questionnaires and interviews.

No clear correlation between noise exposure and myocardial infarction was found in the entire study population. However, once people with impaired hearing or exposure to other sources of noise had been eliminated from the study, it was found that there was a 40% higher risk of myocardial infarction in people exposed to road traffic noise exceeding 50 decibels. This relationship applied independently of other known risk factors for myocardial infarction, such as exposure to air pollutants.

"More research will be needed to establish a definite correlation between road traffic noise and myocardial infarction, but our results are supported by other studies showing the cardiovascular effects of noise, such as those concerning high blood pressure," says Professor Göran Pershagen, who led the study. "Councils should already be taking these results into account when planning new roads and residential areas."

Noise is a serious and growing environmental problem. According to the World Health Organization, some 40% of the European population is exposed to road traffic noise exceeding 55 decibels during the day. There is no threshold limit for road traffic noise in the EU, but in Sweden, the maximum acceptable level is 55 decibels at a building’s façade.

"In the present study, some 65% of subjects were exposed to road traffic noise at levels of 50 decibels or more," says postgraduate Jenny Selander. "This percentage is probably lower for the country as a whole, given that the subjects all came from in and around Stockholm, but there is still a considerable proportion of the population who are being exposed to noise."

The study has been published in the online edition of Epidemiology and will go to print in March.

Selander J, Nilsson NE, Bluhm G, Rosenlund M, Lindqvist M, Nise G, Pershagen G. Long-Term Exposure to Road Traffic Noise and Myocardial Infarction. Epidemiology, Epub ahead of print, December 29, 2008.

[Source: Karolinska Institutet]