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Noise and cardiovascular diseases

The vegetative brain centres can be activated directly by noise signals from the ear without undergoing any or only limited processing. In particular short and impulsive noises appear to have the most direct impact. In most other cases, the brain takes the time to evaluated the content of the noise. The information is compared to previous experiences with similar noise events and the result is stored and evaluated. Emotional and physical reactions are the outcome.

The autonomic nervous system controls bodily functions involuntarily. In other words, you can't do much about it. One part of this system is the sympathetic nervous system which reacts to, let's say a loud and impulsive noise, by initiating the release of the stress hormones adrenaline (epinephrine) and  noradrenaline (norepinephrine).

In a ten-year study, Professor Christian Maschke of the Robert Koch Institute in Berlin, Germany, confirmed the association of noise and cardiovascular diseases. He collected medical data from workers in a boiler factory where average noise levels of 90 to 95 dBA and peaks of 120 dBA are common. A control group of workers in the transport industry is exposed to levels of between 50 and 60 dBA. Participants of both groups had no indication of cardiovascular disease at the beginning of the study.

Researchers involved in the study recorded higher levels of the stress hormones adrenaline, noradrenaline, and cortisol in persons exposed to noise. In addition, long-term exposure showed higher levels of cholesterol, triglyceride and fibrinogen.

Not surprisingly, after 13.5 years, 81 workers in the boiler factory developed hypertension to various degrees of severity, compared to only 16 in the control group.  Apart from establishing a clear link between noise and cardiovascular disease, the study also underlined the need for long-term trials, as no significant differences between the two groups could be recorded at around the half-way mark of 6.5 years. It is suggested that at least five years of noise exposure is required to show some effect on the cardiovascular system.  

In other studies, researchers compared the levels of stress hormones and blood pressure of children living near the airports of Los Angeles and Munich with children living in quieter areas. As with the Maschke study, the researchers recorded higher levels of stress hormones and blood pressure in noise-exposed children.

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