Pursuit of Silence - Impact on Your Immune System

I just saw a very interesting documentary film "The Pursuit of Silence".  The film also provided the experience of short scenes of silence juxtaposed to the "noise" that has become part of our everyday lives. 

One of the subjects in the film was research done in Japan by Yoshifumi Miyazaki on "forest bathing" and the positive effects of making contact with and taking in the atmosphere of the forest. The results show that forest environments promote lower concentrations of cortisol (stress hormone), lower pulse rate, lower blood pressure than city environments.  In effect, boosting the immune system. What is the impact of this sound on our health?

According to WebMD, normal conversation is about 60 dB (decibels), a leaf blower is about 90 dB, and a loud rock concert is about 120 dB.  In general, sounds above 85 are harmful, depending how long and how often you are exposed to them.  How does loud sound or noise harm you?

1. Physiologically - loud noises produce cortisol and elevated levels contribute to cardio-vascular disease and other diseases. On the other hand the gentle sound rain on a roof can create a calming effect.

2. Psychologically - one scene in the film showed a street scene in Mumbai, the noisiest city in the world, during a festival with noise well over 100 decibels. This noise causes distress to the elderly and infants, and a sad story shared in the film of a young girl being raped, whose screams were not heard over the din of street noise.

3. Cognitively - in a public school next to track with trains going past every 5 minutes, the average noise level was above 85 dB. In the US, sounds above 55 are considered harmful.  Test scores of students are lower and reading skills are many  months  behind their peers in schools without overhead air traffic or next to train tracks.

Noise and sound pollution has a huge effect on our health, however, we are unaware of the ill effects until chronic exposure leads to a profound health issue including hearing loss.  Protect yourself from noise by wearing protective earplugs when exposed to loud sounds like mowing the lawn with motorized mower or attending loud rock concerts or more recently in the Bay Area when viewing the Blue Angels fly over during Fleet Week.  

The effect of silence or at least gentle sounds like birds singing or leaves rustling in the breeze in a forest, produce a calming effect and positive physiological effects, increase  productivity, and in a 2013 study by Imke Kirst, "Is Silence Golden? Effects of auditory stimuli and their absence on adult hippocampal neurogenesis", 4 groups of mice were exposed to sound, but the one group of mice that had silence showed new brain cell growth.

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