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Winter 2006

Happy, quiet New Year!

Noise may increase risk of heart attack

Noise hurts! Too much noise may increase the risk of heart attack, European researchers say. In a large case-control study, chronic exposure to environmental noise was associated with an increased risk of myocardial infarction in both men and women, according to Stefan Willich, M.D., of the Charite' University Medical Centre, Berlin.

According to the study, the culprit was the noise itself, not the annoyance the noise caused. Dr. Willich and colleagues report in the Nov. 24 online edition of the European Heart Journal. To study the issue, the researchers enrolled consecutive heart attack patients in Berlin's 32 major hospitals, and matched them with controls admitted for other conditions not thought to be linked to noise, such as inguinal hernia or goiter.

Data on annoyance from noise was obtained through standardised interviews with the 4,115 patients. Data on noise exposure was obtained from a variety of sources, including traffic-noise maps and international standards for workplaces. At work, chronic exposure to noise was only associated with increased heart attack risk in men. However, the risk did not rise in step with increasing noise levels, Dr. Willich said. "We seem to be looking at a threshold at which risk occurs and remains constant above this," he said. The risk threshold is around 60 decibels, or about the level of noise in a large busy office, he said.

After adjusting for other risk factors, the investigators found:

  • Men exposed to high environmental sound levels had about a 50% greater heart attack risk than did those in the reference group (exposed to less than 60 db). The odds ratio was 1.46 with a 95% confidence interval ranging between 1.02 and 2.09.
  • For women, exposure to high environmental sound levels more than tripled the risk. The odds ratio was 3.36 with a 95% confidence interval ranging between 1.40 and 8.06.
  • For men at work, exposure to high sound levels increased the risk by about 30%, compared with a reference group exposed to sound levels of less than 55 decibels. The odds ratio was 1.31 with a 95% confidence interval ranging between 1.01 and 1.70.

    The researchers also found that the level of annoyance people felt at high noise levels wasn't a factor. In neither men nor women was there a significant link between annoyance and increased risk of heart attack. However, Dr. Willich said, for women there was a trend toward risk increase because of annoyance: the adjusted odds ratio was 1.47, with a 95% confidence interval ranging from 0.95 to 2.25. Most previous studies have focussed on men, he said, and this was the first study to show an effect in women. The findings raise the possibility of a "gender-specific reaction and pathophysiological response", which needs to be investigated further, he said.

    The study was limited, Dr. Willich said, in that it didn't look at transitional noise exposure - such as driving to work on a busy expressway - and didn't include rural populations or people over 70. The U.S. Occupational Safety and Health Administration says workers can be exposed to 90 decibels for as long as eight hours. The equivalent standard in Europe is 85 decibels. But this study implies that both standards are too high, Dr. Willich said. "We should definitely be looking at something lower," he said, "somewhere between 65 and 70 decibels."

    Source reference: Willich SN et al. Noise burden and the risk of myocardial infarction. European Heart Journal, Nov. 2005.

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