The Sound of Stress

High-pitched sound raises the stress hormone cortisol while low-pitched sound reduces it according to a small pilot study presented at the joint International Congress of Endocrinology and European Congress of Endocrinology in Florence, Italy.

An Italian research team found that 86% of its test subjects had decreased cortisol levels after an hour listening to a low-frequency sound. 65% of the same testers experienced an increase in cortisol after exposure to a high-frequency sound for a similar length of time.

The researchers focused on simple sound waves – not music, as many previous studies have done – adding evidence to their theory that it’s the physical properties of sound, not the appreciation of melody, that cause a physiological response in humans.

The human ear is capable of hearing frequencies ranging between approximately 20 hertz (the lowest note on a large pipe organ) to 20,000 hertz (a high shrill dog whistle). Low frequencies (a bass drum, thunder, a deep man’s voice) and high frequencies (a squeak, squeal, or high woman’s voice) are registered at different locations inside the cochlea, the auditory portion of the inner ear.

This study exposed 30 healthy testers (mixed gender, age, and lifestyle) to different sound frequencies modulated with a sequencer. Three evening sessions were spaced out by three- day intervals: the first session tested low-frequency sound waves (40 to 115 hertz) and the second session looked at high-frequency sound waves (8200 to 8500 hertz). The third control session used radio music adapted from three FM channels (mixed low-frequency sound waves).

The testers refrained from eating, drinking alcohol or caffeine, smoking and physical exercise in the eight hours prior to each session. After 30 minutes of relaxation, an initial blood sample was taken at 20:00. Sound was then played at a high volume of 1000 watts. Blood samples were taken again after 40 to 60 minutes while the sound continued to play. The high-frequency group was allowed five minutes of silence in between two twenty minute sessions. They were also given ear plugs to prevent inner ear damage. At the end of each session participants filled out a questionnaire designed to analyse their emotional reaction to the experience.

The results confirmed that exposure to sound waves can change blood cortisol levels in both directions depending on the frequency used. In the first and third low-frequency groups there was a reduction in cortisol levels (evidenced in 86% and 72% of testers, respectively). Cortisol dropped an average of 26% from the base reading in the first session and 18% in the third session. In the second high-frequency group 65% of testers experienced an increase in cortisol levels, which rose an average of 37%. Although the participants ranked both the second and third sessions as unpleasant, only the second session saw an increase in cortisol levels, suggesting that the sound wave was responsible for the cortisol shift and not the participant’s emotional status.

Cortisol is an important hormone which regulates a wide range of processes throughout the body including metabolism, immune function, and blood pressure. It also plays a crucial role in helping the body react to stress and has been dubbed the “stress hormone” because it is secreted in higher levels during the body’s “fight or flight” response. Blood levels of cortisol vary but are generally high in the morning and fall throughout the day. Small increases in cortisol can help the body effectively respond to stress, but raised cortisol levels in the long term can cause wide-ranging health problems.

The results of this research pave the way for a larger study to confirm the findings as well as explore the medical benefits of sound waves. Further analysis will also look more closely at statistical differences related to age and sex.

Researcher Dr Chiara Olcese said:

“Searching for links between neuroscience, endocrinology and music is not only interesting and curious – it may also be useful for medical treatment in the future. Our study shows that the frequency of sound can potentially affect a person’s cortisol levels, with higher frequencies raising production of this hormone. We now need to carry out further work to examine in more detail the medical implications of this work. I hope that people will become more aware of the power of sound and the unseen effects that it can have on the body.”