Abstract
The mobile phone is a ubiquitous piece in this modern world. An estimated 85% of Americans, 80% of the British, and perhaps 75% of Indians use it, as of today. Mobile phones communicate by transmitting radio waves through a network of fixed antennas called base stations. Radio frequency waves are electromagnetic fields, and unlike ionizing radiation such as X-rays or gamma rays, can neither break chemical bonds nor cause ionization in the human body. 1000 participants from outpatient department of a tertiary care center over a period of one and a half years, were included in the study and were divided equally into case (> 1 year use) and control (< 1 year use) groups. Out of 500 cases, maximum 233(46.6%) subjects were using mobile since last 4–6 year and 134(26.8%) were using mobile since last 7–9 year and maximum 344(68.8%) subjects were using mobile 1–3 h/day and 145(29.0%) were using mobile 4–6 h/day.
Keywords: Hours of exposure, Mobile phone, Sensorineural hearing loss, Years of exposure, SAR
Introduction
Mobile phones are low-powered radiofrequency transmitters, operating at frequencies between 500 and 2700 MHz with peak powers in the range of 0.1–2 Watts. The handset only transmits power when it is turned on. The power (and hence the radiofrequency exposure to a user) falls off rapidly with increasing distance from the handset. A person using a mobile phone 30–40 cm away from their body—for example when text messaging, accessing the internet, or using a “hands free” device—will therefore have a much lower exposure to radiofrequency fields than someone holding the handset against their head [1].
Mobile phones transmit and receive microwave radiations at frequencies mainly ranged between 800 and 2000 MHz, which excites rotation of water molecules and some organic molecules, causing thermal and non-thermal effects on humans. The reported thermal effects from mobile phones include headache, sensation of burning or warmth of the ear, burning sensation in the facial skin and alteration in the blood–brain barrier. The auditory system is in the close proximity to the mobile phone so that hearing is potentially the most affected target of thermal and non-thermal effects. The external ear may provide a natural route by which EMFs from mobile phones may reach the peripheral and central auditory system, leading to relatively high energy deposition in the ear [2–7].
The auditory system and particularly the cochlear outer hair cells (OHC) are known to be highly sensitive to a great variety of exogenous and endogenous agents and externally applied electric and magnetic fields are known to be able to produce some hearing sensation. Higher frequency is localized at base of cochlea and lower frequency is localized at cochlear apex [8–10].
Measurement of the Radiofrequency Dose
The specific absorption rate (SAR) is used to measure the energy dose that subjects exposed to RF absorb. The SAR is expressed in power (Watts) by tissue mass (kilograms).
The full body SAR in human beings depends on various factors, such as: the nature of an electromagnetic field (low or high frequency); the distance and spatial orientation of the field relative to a subject; the subject’s geometry and the water content of different tissues. The SAR also varies according to the mobile phone handset model, the transmission system technology (analog or digital), the distance between a user’s head and the handset antenna, and the distance between a mobile phone and its base station. Digital handsets (TDMA—time division multiple access, CDMA—code division multiple access, and GSM—Global System for Mobile Communications) expose a user’s head to a SAR almost always below 1 W/kg, well below the recommended maximum safe exposure limits. Radiological protection committees from various countries have tended to set the SAR tolerance limit at 10 W/kg [11]. SAR can be estimated in mobile phone by typing *#07#.
Materials and Methods
A total of 500 individuals were included in study. The individuals were divided into two groups: individuals who use cell phones for 1 year and talk for at least 1 h daily and in other group individuals who use cell phones for less than 1 year. The individuals were between 20 and 40 years of age. Careful history was taken and clinical examination was done and finally pure tone audiometry was conducted in case and control group. Variables used in studies are Age, sex, occupation, duration of use, tinnitus, and pain. Statistical analysis was done using Statistical Package of Social Science (SPSS Version 20; Chicago Inc., USA). Data comparison was done by applying specific statistical tests to find out the statistical significance of the comparisons. Quantitative variables were compared using mean values and qualitative variables using proportions.
Results
This study was conducted on 1000 participants with the aim to study adverse effect of mobile phone on hearing in healthy individuals. The individuals were between 20 and 40 years of age. Out of 1000 study subjects, 500 were cases who were using mobiles for more than 1 year and 500 were controls who were using mobiles less than 1 year. Among 500 cases, maximum were 26–30 year and 36–40 year old i.e. 181 (36.2%) and 167 (33.4%) respectively. Whereas out of 500 control most were in age group of 20–30 years (Fig. 1).
Fig. 1.
Demographic distribution of study subjects according to age and duration of using mobile
Among cases, 334 (66.8%) were male and 166 (33.2%) were females while among controls 285 (57.0%) were females and 215 (43.0%) were male. There was statistically highly significant difference in the distribution of study subjects according to gender and duration of using mobile phones with male propensity (P = 0.001) (Fig. 2).
Fig. 2.
Demographic distribution of study subjects according to gender and duration of using mobile
Mean SAR of mobiles used by cases were 1.016 ± 0.457 while mean SAR of mobiles used by controls were 0.973 ± 0.462. Its range was 0.10–1.60. There was statistically no significant difference between cases and control in mean SAR (P = 0.139) (Table 1). Out of 500 cases, maximum 233 (46.6%) subjects were using mobile since last 4–6 year and 134 (26.8%) were using mobile since last 7–9 year (Fig. 3).
Table 1.
Mean SAR of mobiles used among cases and control
| Groups | SAR | ||
|---|---|---|---|
| Mean | SD | Range | |
| Case (using mobile > 1 year) | 1.016 | 0.457 | 0.10–1.60 |
| Control (using mobile < 1 year) | 0.973 | 0.462 | 0.10–1.40 |
| Total | 0.995 | 0.460 | 0.10–1.60 |
| Student ‘t’ test value | 1.481 | ||
| Significance ‘P’ value | 0.139 (NS) | ||
Fig. 3.
Distribution of case according to years of exposure
Maximum 344 (68.8%) subjects were using mobile 1–3 h/day and 145 (29.0%) were using mobile 4–6 h/day. Incidence of hearing loss was 1.8%. Out of 500 cases, hearing loss was found in 9 (1.8%) cases and 491 (98.2%) were normal. Out of 9, 3 (0.6%) were 20–25 year and 36–40 year old and only 1 were 31–35 year. Among cases with 1–3 h of exposure, incidence of hearing loss was 5 (1.0%) while among cases with 4–6 h of exposure, incidence of hearing loss was 4 (0.8%). There was statistically highly significant difference in incidence of hearing loss according to hours of exposure and degree of hearing loss (P = 0.003) (Table 2).
Table 2.
Incidence of hearing loss according to hour of exposure and degree of hearing loss
| Hour of exposure | Degree of hearing loss | ||
|---|---|---|---|
| 56–65 dB | 66–75 dB | Total | |
| 1–3 h | 5 (1.0%) | 0 (0.0%) | 5 (1.0%) |
| 4–6 h | 0 (0.0%) | 4 (0.8%) | 4 (0.8%) |
| Total | 5 (1.0%) | 4 (0.8%) | 9 (1.8%) |
| Chi square value | 9.00 | ||
| Significance ‘P’ value | 0.003 (HS) | ||
Discussion
The widespread use of mobile phones has been going sky-high over the past decade and now its use is an essential part of business, commerce, and society. Widespread concerns have been raised about the possibility that exposure to the RF fields from mobile phones or their base stations could affect people’s health as there has been the rapid growth of the mobile telecommunications.
Braune et al. have reported acute effects on blood pressure in human volunteers exposed to a conventional GSM digital mobile phone positioned close to the right side of the head. The study and control groups were found to be comparable with respect to the age and sex distribution.
In our study, age group considered is 20–40 year. In 2002 Thomas and Andrew of Canada conducted a study on 100 male and 100 females in age group of 17–45, regarding adverse effect of mobile phone on hearing sensitivity and brain. They found that maximum age group affected is 20–35 which also matches with our study (20–30).
In our study most of the individuals were asymptomatic. In a study conducted by l-Khlaiwi et al. [12], the overall mean percentage for presenting complaints in all chronic mobile users were headache (21.6%), sleep disturbance (4%), tension (3.9%), fatigue (3%), and dizziness (2.4%). Meo and Drees in a study showed about 34.59% of problems were related with impaired hearing, earache and/or warmth on the ear, and 5.04% of complaints with decreased and/or blurred vision.
In our study 1.7% of subjects had SNHL who were using mobile phones for 4–6 years while no hearing loss was noted in subjects using mobile phones for less than 3 years. This indicates that the moderate severe hearing loss (55–65 dB) noted in the study group depended not only on years of exposure, but also on hours of exposure per day and type of mobile and its SAR. This correlates with the findings of Panda et al. [13]. He assessed the effects of chronic exposure to electromagnetic waves emitted from the GSM mobile phones on the auditory function in users. No significant differences were found for high frequency hearing loss, distortion product oto-acoustic emissions (DPOAE), auditory brain stem response (ABR), in the overall users. High frequency hearing loss was seen in subjects using the phone for more than 4 years (P = 0.04).
However, there appear to be no harmful effects of mobile phone usage on their audiovestibular systems within exposure range of the study, in so far as can be detected by the self-report method employed.
In a study by Sievert et al., to investigate the biological effect of the high frequency radiation produced by the GSM mobile phone on the inner ear with its sensors of the vestibular and auditory systems showed that the electromagnetic fields generated in using the mobile phone do not have an effect on the inner ear and auditory system to the colliculus inferior in the brain stem and on the vestibular receptors in the inner ear and vestibular system. In our study Maximum incidence was seen among subjects with 1–3 and 4–6 h of exposure. Out of 9 subjects with hearing loss, 5 (1.0%) were using mobiles 1–3 h/day and 4 (0.8%) were using mobile 4–6 h/day. There was statistically no significant difference in the incidence of hearing loss according to hours of exposure (P = 0.552). This relates to the study by Callejo and Santamaria [14] in a group of 323 healthy and normoacoustic volunteers who were usual customers of mobile phone for whom an audiometric evaluation was made at the beginning of its use and 3 years later, inquiring about the periods of time per day and ear employed on direct contact contacts with the phone. A healthy and normoacoustic control group of non-users was studied too and study found no significant difference in hearing loss according to exposure hour.
Conclusion
With the increase in use of mobile phones there is increasing concern about their safety. Although our study did not show any significant hearing loss in mobile phone users since 0–25 dB hearing loss is taken for all practical purpose as normal, but we observed significant moderate to severe hearing loss in those participants exposed to mobile phone usage of more than 4 h/day, for continues 4–6 years. Hence we recommend a follow up study in long-term and long duration mobile users before we can come to a definitive conclusion.
Compliance with Ethical Standards
Conflict of interest
Shalini Jadia, Sadat Qureshi, Leena Jain, Mritunjay Shringirishi declare that they have no conflict of interest.
Ethical Approval
All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.
Informed Consent
Informed consent was obtained from all individual participants included in the study.
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