It is not only the volume or sound level that is important.
One other crucial factor is the controlability of the noise.
Noise that cannot be escaped/avoided, or is unexpected, or random, causes more stress to the individual.
One wonders if the true impact of increasing noise intrusion into our lives has yet been well understood.
Perhaps, without the noise, even metrics such as levels of immune-system response might be far higher.
If constant noise, and increased noise, and random noise does cause a depressed immune-system response..then...
My next question is whether there is any correlation between living in a very noisy environment and cancer rates....
heart disease, etc.
For sure there is a correlation between noise and certain apparent learning disabilities.
Further investigation is needed.