Tuesday July 20 2010
There was no clear link between mobile phone use and tinnitus
“Talking on a mobile phone could dramatically increase the risk of the agonising ear disorder tinnitus,” says the Daily Mail.
This news story was based on a very small study that compared the mobile phone usage of 100 people with tinnitus with that of 100 people without tinnitus. The risk of tinnitus did not appear to bear a relationship to using a mobile phone for more than 10 minutes a day, having ever used a mobile phone, or the number of calls a person made. While there was a borderline association between the risk of developing tinnitus and using a phone for more than four years, this remains questionable.
Overall, the lack of clear associations and the small study size mean this research does not provide sufficient evidence to suggest that mobile phones increase the risk of developing tinnitus.
Where did the story come from?
The study was carried out by researchers from the Medical University of Vienna, which also funded the research. It was published in the peer-reviewed journal Occupational and Environmental Medicine.
The BBC highlighted that this was a small study, but all of the news reports, including the BBC’s, emphasised ‘increased risks’ that were, in fact, not statistically significant. The Daily Mirror reported that, of the subjects with tinnitus, “virtually all were mobile phone users”, but did not point out that virtually all of the people without tinnitus were mobile phone users too.
What kind of research was this?
This was a case-control study that investigated whether there was an association between using a mobile phone and developing tinnitus.
Tinnitus is the sensation of hearing sounds (like roaring, hissing or ringing) that are not generated by the outside world but by malfunctions in a section of the inner ear called the cochlea. The cochlea is the part of the ear that normally converts sound waves into nerve signals for the brain to interpret.
The cause of tinnitus is not fully known but, in certain cases, the problem is associated with some ear diseases, head injury, exposure to loud sounds or the use of certain medications.
The researchers say that mobile phones could be a risk factor for tinnitus because the cochlea may, theoretically, absorb microwave energy and be affected by prolonged exposure to electromagnetic fields.
What did the research involve?
The researchers recruited 100 patients with chronic tinnitus who attended an outpatient ear, nose and throat clinic in Vienna, Austria. Chronic tinnitus was defined as tinnitus lasting for longer than three months. The patients were aged between 16 and 80 years.
For each case (person with tinnitus) the researchers recruited a control (a person who did not have tinnitus) of the same age, gender and ethnic group. The controls were attending the ear, nose and throat clinic for other conditions, such as speech problems, sore throats or for a consultation before they had their tonsils removed. The study did not include cases or controls who had diseases of the middle ear, retrocochlear disease, psychiatric diseases, those who had recently had middle-ear surgery, or people with severe but non-ear-related diseases. Some drugs can affect tinnitus, so people receiving these medications were also excluded from the studies.
For each case, the researchers took a medical history focusing on tinnitus and its risk factors. They examined the ear, nose and throat and performed a hearing test (to assess how well the patients could hear pure tones and distinguish speech). They tested the stapedius reflex (an involuntary muscle contraction in response to a loud sound). Additionally, they asked the cases to give a subjective rating of their tinnitus and performed tinnitus-matching, a process in which the researchers played different types of sounds and the patients matched the sound that had the most similar characteristics to their tinnitus.
To assess the person’s mobile phone habits, the researchers used a standardised questionnaire (based on the protocol for the World Health Organization’s Interphone Study). They looked at the cases’ mobile phone usage up to the date when their tinnitus started.
The researchers used an established statistical technique called logistic regression to assess whether there was an association between mobile phone use and tinnitus. They made several adjustments in their statistical model, including for number of years in education and living in an urban area. They propose that “mobile phone use correlates with socio-economic status and the area of living is associated with intensity of exposure because, on average, the output power of mobile phones is higher in rural areas”.
What were the basic results?
The researchers found that, at the time of their study, almost all of the participants had a mobile phone (92% cases, 93% controls). However, at the time of the first occurrence of tinnitus in the cases (and the same date in their matched controls) 84% of cases and 78% of controls were using a mobile phone.
There was no significant difference in the risk of developing tinnitus associated with:
- ever using a mobile phone
- intensity of mobile phone use
- number of calls made
The researchers found that using a phone for four years or more increased the risk of developing tinnitus, but this was of only borderline significance (odds ratio 1.95, 95% confidence interval [CI] 1.00 to 3.80).
How did the researchers interpret the results?
The researchers said that the prevalence of tinnitus has increased over the past decade and is currently 10-15% in industrialised countries. They say that the rise in incidence may be due to better awareness of the condition and better diagnostic tools, but there may also be environmental factors that have contributed to the increase.
They suggest that their results indicate that high intensity and long duration of mobile phone use might be associated with tinnitus, and that “mobile phone use should be included in future investigations as a potential risk factor for developing tinnitus”.
This was a small case-control study that found no association between tinnitus and ever using a mobile phone, the intensity of mobile phone use or the number of calls made. It found a marginally significant association between using a mobile phone for more than four years and an increased risk of developing tinnitus. However, the small size of the study means that it is difficult to draw firm conclusions about the risks of developing tinnitus and whether there is any true association with mobile use.
The researchers also highlight that their study had several limitations:
- They asked the cases and controls to recall their mobile phone usage retrospectively. This may mean that the participants under- or over-estimated their mobile phone use habits.
- Different types of mobile phones may have different output power. Phone characteristics may also have changed over time. The researchers did not make allowances for this in their analysis.
- The researchers did not make allowances for other factors that may have influenced the likelihood of developing tinnitus, such as the use of portable music devices or exposure to loud music or noise. However, the researchers did say that they excluded people with hearing loss, which can result from exposure to loud noise.
As it stands, this study does not provide sufficient evidence to suggest that mobile phones increase the risk of developing tinnitus.