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Could Radio Frequency radiation impair the auditory system?

 

 

 

אישה מדברת בטלפון סלולרי כשהוא צמוד לאוזןIllustrative picture: a woman speaking on cellphone placed next to her ear    

 

According to World Health Organization (WHO) data, about 5% of the world’s population has  hearing loss caused by a variety of genetic and environmental factors. Because cellphones are mostly located next to the head during a call - specifically next to the ear - and the auditory system absorbs the radiation emitted by them, the possibility that exposure to cellphones might cause auditory system impairment or development of tinnitus (a phenomenon where “ringing in the ears” is experienced in the absence of external auditory stimulus) has been investigated.

 

 

 

The scientific literature includes studies where people or animals were exposed to RF radiation for relatively short periods of time and the effect on the auditory system was assessed using various hearing tests. There are also observational epidemiological studies that investigated the possible association between RF radiation exposure and hearing impairment.

The results of existing research on this subject are not conclusive. Considering the small amount of studies in this field and methodological problems affecting some of the studies we recommend acting according to the precautionary principle and minimizing exposure of the ear to RF radiation emitted from cellphones. The most efficient way of minimizing exposure is distancing the phone from the head.

 

 

 

 

Anatomy of the ear and soundwave conduction pathway

The ear comprises three parts: the outer ear, the middle ear and the inner ear. The main function of the outer ear and the middle ear is to transmit soundwaves from the environment to the inner ear. The soundwaves are captured by the auricle of the outer ear and transmitted via the auditory canal to the tympanic membrane. Movement of the tympanic membrane because of sound stimuli leads to movement of the three tiny ossicles in the middle ear and movement of fluids in the inner ear. As a result of the fluids movement, the inner hair cells in the organ of Corti in the cochlea are stimulated, and the impulses that they transmit are converted to nerve signals that are sent to the brain via the auditory nerve.   

                  Structure of the ear

 

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Is there an association between cellphone use and hearing loss?

Hearing loss

According to the World Health Organization (WHO) about 360 million people (constituting over 5% of the world’s population) have hearing loss. Hearing loss is defined as hearing loss of more than 40 decibels (a measure of sound intensity) in the ear with better hearing for adults and more than 30 decibels for children.

 

Hearing loss is divided into two main types depending on the cause: air conduction disturbance and nerve conduction disturbance. Hearing impairment due to air conduction disturbance usually involves abnormality in the outer ear or middle ear and there is usually a mechanical cause. In contrast, hearing impairment due to nerve conduction disturbance (constituting the majority of cases of hearing impairment) usually stems from permanent damage to the cochlear hair cells of the inner ear.

 

Hearing loss is caused by a variety of genetic and environmental causes. Genetic causes include DNA changes or changes in regulatory elements involved in development, structure and normal function of the ear. Environmental causes include lack of oxygen at birth, inappropriate use of certain drugs during pregnancy or infections during pregnancy, exposure to high intensity sounds, viral infection, collection of fluid in the ear, head or ear injury, aging, ototoxic drugs and wax or other foreign bodies blocking the ear canal.

 

Studies assessing the association between RF radiation and hearing loss

This subject was investigated in epidemiological studies, in trials in humans and in animals. Some of the studies investigated hearing loss due to disturbed air conduction and some studied hearing loss due to disturbed nerve conduction.

 

Studies in humans

In order to assess whether RF radiation affects the auditory system, various audiology test results were compared before and after minutes or hours of exposure to RF radiation emitted from cellphones. Some of the studies included an additional group of patients with sham exposure, where neither the subjects nor the researchers knew when there was real exposure to RF radiation or no such exposure.

 

In a study conducted in Saudi Arabia and published in 2013, Alsanosi et al. found that one-time exposure of 60 subjects aged 18-26 years to RF radiation for 60 minutes affected auditory stimulus threshold and acoustic reaction of the inner ear hair cells, but it was not clear if the effect observed was temporary or permanent. In contrast, other studies did not find exposure to RF radiation to have any effect on audiology test results.

 

The main limitations of these studies are short duration of exposure to RF radiation and limited sample sizes in most studies.

 

Epidemiological studies

In order to assess the possible association between prolonged cellphone use (months or years) and auditory system impairment, studies have been conducted where information was gathered simultaneously on cellphone usage habits and participants’ hearing via questionnaires or through audiology tests. This type of study, where information on exposure and results of exposure are gathered at the same time point is called a cross-sectional study. Some of these studies found that exposure to RF radiation did not have any effect on the auditory system while others did show an effect.

 

In a study published in 2013, 52,680 mothers in Denmark were asked to complete questionnaires addressing lifestyle, including cellphone usage and environmental exposure. Each mother was asked to estimate the extent of her child’s cellphone usage at age 7 in the question “Does your child use a mobile phone?” (Response options were “No, never”, “Yes, but less than one hour per week”, “Yes, more than one hour per week”).  Hearing loss was evaluated with the question: “Does your child have permanent hearing loss?” It is important to note that these are very general questions that do not allow quantification of RF radiation exposure and nature of hearing was evaluated very crudely. Results of the study showed a borderline statistically significant association between cellphone radiation exposure and hearing loss at age 7 (Relative Risk: 1.21, 95% confidence interval 0.99-1.46). In addition it is important to note that in this type of study it is not possible to draw conclusions regarding association causality since it is not clear what caused what: Did the cellphone exposure cause hearing loss or did the hearing loss lead to reduced cellphone usage? Also the mothers’ self-reporting on cellphone exposure and children’s hearing constitutes a limitation in this study.

 

An additional cross-sectional study conducted in India and published in 2010, compared audiology test results for 112 adults who reported on their cellphone usage and audiology test results for 50 adults who had never used a cellphone. There were no differences found between results of audiology tests in the two groups. It is noted that in the group of cellphone users, a higher incidence of hearing problems was observed amongst those aged over 30 years, those who reported daily cellphone use of 60 minutes or more and those who had used a cellphone for over 4 years.

 

In a study published in 2006, Davidson et al. asked 117 University students in Britain about their cellphone usage habits (when they had first started using a cellphone, number of minutes use per day etc.) and their hearing (for example the student was asked to estimate how hard it was for him to understand someone who is a clear speaker in a quiet room, or how easy it would be for him to follow somebody's conversation when other people are talking close by). This study did not find a higher rate of hearing problems amongst participants who reported high levels of cellphone use compared to those who reported lower levels of use. It is important to remember that the self-reporting by participants of their cellphone usage habits and of their hearing constitutes a limitation in this study, as both recall bias and subjectivity of hearing assessment may have influenced the study results.

 

A study published in 2006 investigated the effect of RF radiation exposure from cellphones on the auditory system amongst 60 men aged 22-53 years. Estimation of cellphone exposure was based on participants’ self-reporting. The researchers assessed participants’ hearing acuity using a hearing test that evaluates hearing of various tones (pure tone audiometry), and an electrophysiological hearing test that evaluates electrical activity in the auditory nerve and the brainstem as a response to auditory stimulation (brain stem evoked response audiometry). Amongst participants who reported speaking on cellphones for about two hours a day for four years reduced response was observed to 4000 Hz frequency tones in the right ear and to 500 Hz and 4000 Hz frequency tones in the left ear versus the group of participants who only spoke for about 10-20 minutes per day and those who did not use cellphones. Despite this, no differences were found between the groups in the results of the test that examined the electrical activity in the auditory nerve and brainstem as a response to auditory stimulation. 

 

Animal studies (in vivo)

In several studies where rats were exposed to RF radiation at frequencies of  cellphones (usually 900-1800 MHz) for about 1-6 hours over a period of 30 days no effect of RF radiation on  the auditory system were detected. In contrast, Ozgur et al. reported that in rats exposed to RF radiation of 1800MHz continuously for a month, damage was observed to the nerve cells in the cochlea of the inner ear, but no behavioral or neurological changes were observed in these rats. It is possible that the difference in the study’s results stemmed from the fact that in Ozgurs’ study there was continuous exposure to RF radiation 24 hours a day, and not for relatively short time periods like in other studies. Also it should be noted that auditory system evaluation in Ozgur’s study was performed using a different hearing test to that used in other studies. 

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Is there an association between cellphone use and tinnitus?

Tinnitus

Tinnitus is a phenomenon where a person experiences the sensation of sounds in the ear (“ringing in the ears”) without an external auditory stimulus. The prevalence of the phenomenon in adults is between 10-30%, and the number of people affected by this phenomenon is gradually rising. Tinnitus is divided into two types: subjective tinnitus, which cannot be diagnosed in audiology testing, and objective tinnitus, which can be diagnosed in this testing. Subjective tinnitus is more common than objective tinnitus, and its cause is unknown. Most people develop tinnitus after deterioration in hearing. 

 

Several environmental causes may increase the chances of developing tinnitus, first and foremost noise. It is suspected that RF radiation emitted from cellphones may increase the risk of developing tinnitus.

 

Studies examining the association between RF radiation and tinnitus

A Prospective  cohort study conducted in Switzerland and published in 2012 included 1375 participants who completed self-reporting questionnaires to investigate whether an association exists between personal or environmental exposure to RF radiation and development of tinnitus. This study did not find an association between RF exposure and development of tinnitus. 

 

A case control study published in 2009 including about 200 participants investigated whether an association exists between electromagnetic radiation exposure, radiation hypersensitivity and tinnitus. The study investigated a possible association between environmental exposure to RF radiation and development of tinnitus, but did not find an association. Tinnitus was evaluated in the study using participant self-reporting (they were asked if they suffered from tinnitus, and if so, for how long) and severity was evaluated by questionnaire. The study also evaluated whether people who defined themselves as hyper sensitive to non-ionizing radiation suffer more from tinnitus compared to the control group. The study results showed that there was indeed a greater rate of tinnitus reported in the group of participants who defined themselves as suffering from hypersensitivity to electromagnetic radiation. Amongst those who suffered from tinnitus, no differences were found between the two groups in duration and severity of tinnitus.

 

A case control study published in 2010 and including 200 participants aged 16-80, recruited from the Ear- Nose- Throat Department of the Medical University of Vienna, compared cellphone usage habits of participants suffering from acute or chronic tinnitus to a control group of participants who did not report tinnitus. Cellphone usage habits were evaluated using a self-reporting questionnaire. This study found a significant risk of developing tinnitus (Relative Risk: 1.95, 95% confidence interval 1-3.80) only amongst participants who reported cellphone usage for over 4 years and who spoke on the phone on the same side where they developed tinnitus.

 

Can the structure of the ear explain the results of the studies that evaluated an association between RF radiation and hearing loss or tinnitus?

As mentioned, most of the studies did not find an association between RF radiation and auditory system impairment or development of tinnitus. It is possible that the reason for this lies in the structure of the ear. It has been suggested that since the cochlea is surrounded by very dense bone, contains fluid and is situated relatively deep, it is more protected from cellphone RF radiation and its thermal effect.

 

Can hearing loud voices on the cellphone cause hearing loss?

This article does not discuss the possible implications of hearing loss due to hearing loud voices on cellphones.

 

In summary 

The results of existing research on this subject are not conclusive. Considering the small amount of studies in this field and methodological problems affecting some of the studies we recommend acting according to the precautionary principle and minimizing exposure of the ear to RF radiation emitted from cellphones. The most efficient way of minimizing exposure is distancing the phone from the head.

 

References

Updated on: 24.1.2018