Exposure to microwave radiation from mobile phones cause brain tumors
The life style and quality of life of human beings have changed a lot during the last few decades. Advancements in the area of science and technology have made this possible. Even though this has made life easier for modern man, they bring with them lot of health related issues in the form of many non-communicable diseases. Developments in science happen at such a rapid pace that most of the times the health consequences will be understood very late. The use of mobile phones has dramatically increased during the last 10 years all around the world. Since the introduction of cellular phone services in the 80s, the number of subscribers has steadily increased. But there has been a rapid increase in the number from the year 2000 which almost got doubled by 2004. According to the International Telecommunication Union (ITU), by the middle of 2004 the total number of mobile phone subscribers around the globe crossed 1.5 billion. This comes to around one – fourth of the total world population.
Mobile phones use electromagnetic radiations for functioning and use microwaves as carrier waves. There are two types of mobile phones known as analogue (first generation) mobile phones and digital (second and third generations) mobile phones. Since they are using microwaves, they can raise the temperature in the tissues which are kept close to them. This is explained by the fact that there will be absorption of high energy from electromagnetic radiations, which is dependent on electromagnetic field strength, wavelength of the electromagnetic waves and dielectric properties of the tissues (Kundi et al., 2004). The intensity of energy transfer is found to be higher with the first generation analogue mobile phones compared to the later digital ones. Since majority of mobile users hold the mobile phones close to their ears and use it, there is a concern that this could lead to pathological conditions in the brain.
Health concerns associated with the use of mobile phones include brain tumors, short-term memory, depression, sleep disturbances and tiredness. Of these, brain tumor is the most important pathological condition affecting the health with far reaching consequences, associated with the use of mobile phones. A number of epidemiological studies have been conducted to evaluate the role of mobile phones in the causation of brain tumors. But the existing scenario poses different problems as the population has never been exposed to this much electromagnetic radiation and that too at very close ranges. More over, only two decades have elapsed after the introduction of mobile phones. Due to these reasons the concern of an association between mobile phone use and brain tumor incidence still prevails.
The hypothesis for this research analysis can be stated as ‘there is an increased risk for developing brain tumors with exposure to microwave radiation from mobile phone use’. This research paper will assess the scientific basis of this hypothesis, evaluate the scientific evidence in support of and against this hypothesis, and critically analyze the evidence.
Studies in support of the hypothesis
Many biological studies have shown that there are changes in the brain that includes leakage of blood-brain barriers, increased frequency of micronuclei and activation of heat shock proteins. Studies conducted in rats show that there is significant leakage of albumin through the blood-brain barrier. Neuroanatomical studies conducted in Sweden conclude that mobile phone electromagnetic radiations cause neuronal damage in the cortex, hippocampus, and basal ganglia in the brains of exposed rats (Salford et al., 2003). Human endothelial cell cultures were exposed to mobile phone radiation. It was observed that one hour exposure to mobile phone radiations produced phosphorylation changes in the neurons and there was abnormal expression of heat shock proteins, a protein expressed in the stress response pathway (Leszczynski et al., 2002). The uthors of this study presumed that repeated use of mobile phones over a long period of time could lead to brain tissue damage and brain tumors as the heat shock proteins are well known to facilitate the development of brain cancer by inhibiting the cytochrome c/caspase-3 apoptotic pathway and cause an increase in blood-brain barrier permeability.
Many epidemiological studies also support the hypothesis that there is association between brain tumors and mobile phone use. Hardell et al (1999) published the first epidemiological study showing a relation between brain tumors and mobile phone radiations (Hardell et al., 1999). It was a case control study done in reported cases of brain tumors. The study included 233 brain tumor patients from different parts of Sweden. Matched controls, two for each case, were also selected from the Swedish population. The study concluded that there was increased risk for developing brain tumor with increased use of mobile phones and the authors suggested the possibility of an increased risk for brain tumor in the anatomical area close to the use of a cellular telephone.
Another publication by the same authors in the year 2001 evaluated the association between the side on which the brain tumor was observed and the side on which mobile phone was used. This was also a case control study conducted in 233 patients aged 20 – 80 years with brain tumors. This questionnaire based survey concluded that use of a cellular telephone increased the risk of tumours on the same side in the temporal, temporoparietal and occipital areas, the anatomical areas with highest exposure to microwaves from a mobile phone (Hardell et al., 2001).
Studies were conducted to understand the nature and histopathology of tumors associated with mobile phone use. A case control study was conducted in 649 adult patients identified with malignant brain tumors. 1:1 matching was adopted for cases and controls. All patients were alive during the study period and the tumor characteristics were verified histopathologically. It was concluded that mobile phone use increased the risk of developing a same-sided malignant brain tumor like astrocytoma (Hardell, Mild et al., 2002). Similar studies with 1303 brain tumor patients showed an increased risk for acoustic neurinoma (Hardell, Hallquist et al., 2002) and vestibular schwannoma (Hardell, Hansson Mild et al., 2003) among analogue mobile users.
A later study evaluated whether there was any difference between analogue and digital mobile phones in increasing the risk for brain tumors. The same study assessed the relation between the duration of use of mobile phones and brain tumor incidence. This case-control study enrolled 1617 patients with diagnosed brain tumors. It was found that analogue mobile phones increased the risk for developing ipsilateral astrocytomas, where as digital mobile phones did not increase the risk significantly (Hardell, Mild et al., 2003). When duration of use was analyzed as a continuous variable in the total material, the risk for brain tumors increased per year for analogue phones substantially.
Auvinen et al studied the risk of brain tumors and salivary gland cancer associated with mobile phone use (Auvinen et al., 2002). The study was designed as a population based case-control study. There were 398 brain tumor patients, 34 salivary gland cancer patients and 2160 controls matched for age and sex. The study was conducted in Finland with the help of Finnish Cancer Registry. 61% of the study participants used analogue mobile phones and 32% used digital mobile phones. The remaining patients used both types of mobile phones. These patients were followed up for 2 years and the study concluded that there was a significant risk for all brain tumors with analogue phone use.
Studies against the hypothesis
There are studies with a negative outcome that there is no evidence of an increased risk for developing brain tumors with the use of mobile phones. A cohort study with one year follow-up included 152138 portable bag/car analogue mobile phone users and 133423 hand-held analogue mobile phone users. One of the outcome measures was brain cancer. Exposure assessment was based on company records and outcome assessment was based on National Death Index. The average phone use was 1.9 years. The study did not show any significant association between brain cancer occurrence and mobile phone users (Dreyer et al., 1999). Another hospital based case-control study (Muscat et al., 2000) considered 469 cases with brain cancer and 422 controls and evaluated the risk of brain cancer with mobile phone use using interview method and pathological examinations. 88% of the mobile phones were analogue type phones and 74% of the cases were using mobile phones for less than 4 years. The average phone use was 2.8 years. It was concluded that there was no increased risk for brain cancer cases with mobile phone use.
A well conducted retrospective cohort study evaluated the incidence of brain and nervous system cancer, salivary gland cancer and leukemia patients. 420095 mobile subscribers were enrolled which included 154 brain and nervous system tumors and 84 cases of leukemia. 42% cases were using analogue mobile phones and 58% were using digital mobile phones. 93% of cases were using mobile phones for less than three years. There was no overall increased incidence of brain tumors with the use of mobile phones (Johansen et al., 2001).
The biological studies conducted in rats which show neuroanatomical changes with microwave radiations used radiations which are having more energy than the type of radiations used in mobile phones. These results cannot be extrapolated to human beings as the exposure is far less and the skull thickness is also different in humans compared to rats. Similarly endothelial culture studies which showed the expression of heat proteins in the endothelial cells was conducted using radiations more powerful than the electromagnetic radiations used in mobile phones. Until these effects can be matched with the situations seen in human beings, these results do not hold any power for acceptance in real life situations.
In the case control study published in 1999 (Hardell et al., 1999), 37% of the cases were mobile phone users. But the number of patients selected for the study was less. Telephone interview method was also used, which could have caused some recall bias in outcome evaluation. With a small number of cases, where no adequate measures were considered for overcoming recall bias, the results cannot be considered as valid. The study published in 2001 by the same authors (Hardell et al., 2001) considered the same patient population and assessed the relation of mobile phone use with the laterality of brain tumor occurrence. This questionnaire study has not clearly verified the occurrence of brain tumor pathologically, and adding on to that, the recall bias and the small sample size would have made the objective assessment of brain tumor difficult. In both studies, average use of mobile phone was 5 years.
In studies which considered pathological characteristics of the brain tumors, the average time of mobile phone use was 7 years. These studies have not considered other factors which are well known to cause neurological tumors like exposure to X-rays and occupational hazards due to chemicals. The study was conducted as questionnaire and telephonic interview, which might include a possible recall and response bias.
Auvinen et al concluded that there was a significant risk for all brain tumors with analogue phone use. Since the study was conducted using records from the Finnish Cancer, Registry, the chances of recall bias is less. But there is insufficient data on the classification of cases based on their mobile phone use, and in cases this could have resulted in misclassification of cases. This study was not considering other confounding factors which could have affected the occurrence of brain tumors. More over, majority of brain tumor cases were using mobile phones for less than 2 years. The authors have not correlated the duration of use of mobile phones with age of the patient. This does not explain whether the risk with 2 year mobile phone use is same in younger age group and elderly.
The study by Dreyer et al was considering the overall effect of mobile phone use on the mortality due to many causes (Dreyer et al., 1999). The number of cancer cases was very less and so the study does not have sufficient power to claim that the there is no association between brain tumor occurrence and mobile phone use. More over, since the study was based on company records, there was misclassification of microwave exposure from mobile phones. More than 70% of mobile phone users were excluded from evaluation. So the results are inconclusive.
Muscat et al concluded that there was no increased risk for brain cancer cases with mobile phone use, from the hospital based case-control study. The study did not consider other causes of brain tumor. Even though the power of the study was more than 80%, excluding the glioblastoma cases, the power is less than 20%. Histopathology was not unequivocal in all cases. More over, cases were interviewed within 48 hours after surgery which might have caused some recall bias and response bias in the study. These factors together make results of this study unreliable.
Even though the study by Johansen et al was well conducted, the study excluded 42% of mobile phone subscribers (Johansen et al., 2001). No data on the intensity of mobile phone use was available for analysis. But there was data on the duration of use in the case of digital mobile phones from mobile company records. There was insufficient classification of analogue mobile users based on the mobile use and there was misclassification of exposure based on mobile use in many cases. These are the weaknesses of this study.
A well conducted prospective cohort study with sufficient follow up would be useful in identifying the relationship between mobile phone use and the occurrence of brain tumors. The cases should be adequately classified according to mobile phone use and data regarding mobile phone use should be obtained from mobile phone companies. The studies should be conducted in sufficiently large population, after considering other confounding factors like exposure to irradiation, exposure to industrial chemicals after matching for socioeconomic factors, age and sex. Since age and sex are the most important confounding factors in brain tumors, these should be taken care of when the study subjects are enrolled. There should be objective methods for assessment of outcome measures like brain tumors. Data should be supported by sufficient pathological and radiological findings to measure the objectivity of outcomes. Measures should be adopted to exclude recall bias and response bias from the study measurements. Risk assessment should be correlated with the duration and intensity of mobile use. Studies should be conducted to find out if there is a possible lower limit for duration of use below which there is no increased risk. Studies should be designed to find out the types of cancer that have more risk from mobile phone exposure.
Comparison of tumor growth rate with determinants of mobile phone use should be conducted to avoid bias due to interference if the disease with mobile phone use. If a case control study is conducted, the grades of brain tumors should be also matched between cases and controls to avoid bias caused by the different disease progression rates seen with high grade and low grade brain tumors. Since the radiation levels of different mobile manufacturers may differ, there should be consideration for this factor also when studies are designed. Ideally appropriate exposure meters should be used to evaluate the extent of exposure to different patients and this would give uniformity in evaluation.
Never before in history, were human beings exposed to microwave radiations at very close range. Since mobile phones were introduced in 1980s, there is insufficient time to get concrete data to substantially prove whether there is a relation between mobile phone use and brain tumor occurrence. Even though epidemiological studies point to a moderately increased risk with the use of mobile phone for several years, it is unclear whether this data is dependable due to the interference of recall bias and response bias. The studies which were concluding that there is no association between brain tumor occurrence and mobile phone use either did not have sufficient power to make the claims or the study designs were faulty by excluding many mobile phone users and not taking care of recall bias and response bias. Presently, considering all these studies, the evidence is inconclusive to support of refute the hypothesis that there is an increased risk for developing brain tumors with exposure to microwave radiation from mobile phone use. Studies with more robust designs, considering all precautionary measures to avoid the lacunae that were present in already conducted studies, should be conducted to get an answer for this hypothesis.
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