It has come to my knowledge that you have released a position paper about the effects of low frequency noise and infrasound from wind power.
I would like to draw your attention to my recently published article about migraine and infrasound in the Swedish Medical Journal “Läkartidningen” which is available below.
As you well know, migraine is a polygenetic inherited disease with occasional episodes of headache. It is also well known that people with migraine are more sensitive to sound and light than the normal population, especially during an attack of migraine headache. Futhermore it is a well known fact that pulsating sound and flickering light are strong triggers to elicit an attack of migraine.
Migraine is a very common condition in the population with a 15% prevalence for migraine headache. It is quite obvious that the genetic predisposition is much higher – everyone with a genetic disposition will not suffer from migraine headaches. You may well live with the genetic predisposition and never suffer from migraine headache in all your life.
Recent studies have found that these genetic changes affect among others the Ca-channels. This channelopathie increases the cellular depolarisation and as a result the nerve cells are more sensitive to stimulation – less stimulus is needed to trigger a nerve-potential. The main triggers for migraine are – as we all know – all kinds of sensory stimulation, food containing biogenic amines such as tyramine, glutamine, histamine etc., and increased levels or fluctuating levels of estrogen.
Thus sound is a trigger. Loud noise of varying amplitude is a strong trigger that will increase the neural sensitivity in persons with migraine. For example a teacher with a genetic tendency to migraine in a noisy classroom. After a while all senses will become more sensitive (more sensitive to sound, more sensitive to light, more sensitive to vestibular stimuli for example). Hyperacusis makes the situation in the classroom worse and eventually an attack of migraine headache will appear.
Low frequency noise or infrasound noise is no exception. Even if the sound is not heard the sound pressure will exert the same force on the eardrum as audible sound. The sound waves will be transmitted to the inner ear and hair cells are then stimulated. Even if the stimulation is not recognized as sound it will affect brainstem centres and elicit other sensations.
Infrasound is normally not possible to hear, you more likely will feel it as a vibration. Low frequency sound is possible to hear if the volume (sound pressure in dB) is strong enough. But it is a known fact that there are persons who can hear low frequency sound and infrasound at sound pressure levels of 40 db or less. If you have migraine and have developed hyperacusis it is most likely that you are as sensitive to low frequency sound as to normal sound.
Infrasound from wind turbines has properties that differ from other types of infrasound such as infrasound emanating from natural sources (eg wind, rivers) and from artificial sources including road traffic. Infrasound from road traffic (as well as the other examples) has a continuous, constant character – a kind of constant background noise. Infrasound from wind turbines has a fluctuating character with varying amplitude. Infrasound from wind turbines also has three distinct frequencies with higher amplitude than the average infrasound pressure (blade pass frequencies).
A third issue is that the sound pressure for infrasound and low frequency sound is much stronger than the sound pressure for the sound you can hear (for audible sound). If the measured sound pressure at a given distance is 40 dB for audible sound, then the sound pressure for infrasound is 60–80 dB at the same measuring point. Additionally infrasound is amplified inside buildings by resonance effects.
Thus the conclusion is that low frequency sound and infrasound from wind power has the qualities to trigger increased sensitivity and eventually migraine headache or other migraine-symptoms – such as vertigo or tinnitus (without headache).As migraine is so common in the population, this is a relationship that you can not avoid considering.
Futhermore there is increasing knowledge that continuous stimulation of triggers eventually will create a central sensitisation in the brain with a chronic extremely increased sensitivity to sensory stimulation.
I hope that you will take these facts in consideration and advocate for further studies and work for a safe distance for wind power from homes and workplaces that will protect the public health.
Håkan Enbom M.D. Ph.D