- Are there epidemiological studies showing that RF exposure from base stations is safe?
In general, epidemiology studies of radiofrequency radiation and cancer have not found significant correlations between exposure and cancer. The studies include:
geographic correlation studies that compare cancer rates among areas with different potential exposures to radiofrequency radiation
"cancer cluster" studies
studies of cancer in people occupationally exposed to radiofrequency radiation
users of hand-held mobile phones
Geographic correlation studies
Geographic correlation studies estimate the strength of RF radiation in geographic areas and correlate these estimates with disease rates in these areas. Even when the design of geographic correlation studies is optimal, they are considered exploratory and are not used for determining causality.
The geographical correlation studies done to date show no consistent relationship between exposure to RF radiation and either adult of childhood cancer.
Cancer cluster studies
Reports of clusters of cancer provide little practical information. The major steps in evaluating reports of "cancer clusters" are:
- define a logical (as opposed to arbitrary) boundary in space and time,
- determine whether an excess of a specific type of cancer has actually occurred,
- identify common exposures and characteristics.
The above steps, however, have not generally been followed in studies of RF radiation, and reports of "cancer clusters" are of essentially no value in determining whether exposure to RF radiation is a cause of cancer .
Occupational exposure studies
The majority of the occupational studies of RF radiation exposure have deficiencies in exposure assessments because occupation or job title was used as an estimate of exposure; that is, actual RF radiation exposure levels are not known.
There are four epidemiological studies of occupational exposure to RF radiation that are generally considered to have acceptable design and analysis, adequate sample size, and sufficient follow-up time: Robinette et al, Hill], Milham, and Morgan et al. These four studies do not show statistically-significant associations between exposure to radio-frequency radiation and either cancer in general or any specific kind of cancer.
The other studies of acceptable design (Lilienfeld et al], Lagorio et al, Muhm, Tynes et al, Grayson et al, and Thomas et al) have more limitations in exposure assessment, case ascertainment, or follow-up time; but they also do not suggest that RF radiation exposure increases the risk of either cancer in general or any specific kind of cancer.
Szmigielski studied Polish military personnel who may have had RF radiation exposure. The incidence of cancer of all types, brain cancer, leukemia and lymphoma are reported to be elevated in exposed personnel. Because the methods of data collection and analysis are inadequately described or unsuitable, and because assessment of RF radiation exposure is very deficient, the report does not meet basic epidemiological criteria for acceptability. Elwood also concludes that the methods used in the Szmigielski study may have created a systematic bias "that would be expected to produce an increased relative risk for all types of cancer".
Studies of exposure to mobile phone RF radiation
In 1996, Rothman et al. published a study that reviewed health records of more than 250,000 mobile phone users. They found no difference in mortality between the users of hand-held portable phones (where the antenna is placed close to the head) and mobile cellular phones (where the antenna is mounted on the vehicle). In a 1999 follow-up study the same group examined specific causes of death among nearly 300,000 mobile phone users in several U.S. cities. The investigators found no difference in overall cancer rates, leukemia rates, or brain cancer rates between the users of hand-held portable phones and the users of mobile cellular phones. The only specific cause of death that correlated with use of hand-held mobile phones was death from motor vehicle collisions.
In 1999-2001, three case-control studies evaluated brain cancer in users of hand-held cell phones: the first by Hardell et al the second by Muscat et al and the third by Inskip et al .None of studies found associations between cell phone use and brain cancer, and none found exposure-response trends. In general, the temporal lobe of the brain gets the highest RF radiation exposure in users of hand-held cell phones; Hardell et al reported a non-significant excess of temporal lobe tumors, but Muscat et al and Inskip et al reported a non-significant decrease of these tumors. Hardell et al reported a non-significant excess of temporal lobe tumors on the side of the head where the patients reported using their phones, but Muscat et al and Inskip et al reported non-significant trends in the opposite direction.
In the first of the cell phone studies, Hardell et alanalyzed mobile phone use in 233 Swedish brain tumor patients, some of whom has used hand-held mobile phones for as long as 10 years. This was done as part of a larger study of possible causes of brain cancer (other possible causes evaluated included occupation, radiation therapy for cancer, exposure to diagnostic radiation, and exposure to a wide variety of chemicals). Exposure was assessed by questionnaires, and analyses were based on use of hand-held cellular telephones (use of "hands-free" devices and use in a car with a fixed antenna were not considered to be "exposure"). No elevation of brain tumor incidence was found in users of either digital or analog phones, and no exposure-response trend was observed (see figure below). When analysis was restricted to temporal lobe (or temporal, occipital plus temporoparietal lobe) tumors on the same side of the brain where the cell phone was reported to have been used, a non-significant excess incidence was found. This "handedness" was seen for use of analog phones, but not for the use of digital phones.
Brain Cancer in Cell Phone Users
(Hardell et al, 1999).
Relative risk of brain cancer (odds ratio with 95% confidence interval) in users of hand-held cell phones from the epidemiological study of Hardell et al. The number of cases in the overall analysis, and the sub-analyses are shown in parentheses. The analog phones are either at 450 (NMT 450) or 900 MHz; the digital phones are GSM. The lines highlighted in red are probably the ones most relevant to cancer risk assessment as they look at long-term heavy use.
The line highlighted in blue refers to tumors in the lobe of the brain that should get the highest RF radiation exposure in users of hand-held phones.
The last 4 rows look at which side of the head (L=Left, R=Right) the phone was used on.
In December 2000, Muscat et al published a similarly-designed study of 469 brain tumor patients in the US, some of whom has used hand-held mobile phones for as long as 4 years. Exposure was assessed on the basis of in-hospital interviews. No elevation of brain tumor incidence was found in users of hand-held phones, and no exposure-response trend was observed (see figure below). The incidence of temporal lobe tumors (where RF radiation exposure should be the greatest in users of hand-held phones) was not elevated. There was a non-significant trend for tumors to be on the side of the head where the patients reported using their phones; but when analysis was confined to the temporal lobe tumors, there were fewer tumors than expected on the side of the head where the phones were used.
When Muscat et al analyzed tumors by histopathological type, there was no excess of gliomas (the most common and deadly form of brain tumors); but there was an excess of neuroepitheliomas (see figure below). This increase was not statistically significant. Hardell et al. did not explicitly analyze this histopathological subtype of tumor, but Inskip et al found a decreased incidence of neuroepitheliomas.
Brain Cancer in Cell Phone Users
(Muscat et al, 2000)
Relative risk of brain cancer (odds ratio with 95% confidence interval) in users of hand-held cell phones from the epidemiological study of Muscat et al [138]. The number of cases in the overall analysis, and the sub-analyses are shown in parentheses. The analysis is for a mix of analog (88%) and digital phones.
The lines highlighted in red are probably the ones most relevant to cancer risk assessment as they look at long-term heavy use.
The line highlighted in blue refers to tumors in the lobe of the brain that should get the highest RF radiation exposure in users of hand-held phones.
The last 3 rows look at different histological types of brain tumors.
As soon as Muscat et al was published, NEJM rushed a similar study onto their website that had been scheduled for publication in January of 2001. Inskip et al studied 782 brain tumor patients in a different part of the US, some of whom had used hand-held mobile phones for as long as 5 years.
They found no elevation of brain tumor incidence in users of hand-held phones, and observed no exposure-response trend (see figure below). The incidence of temporal lobe tumors (where RF radiation exposure should be the greatest in users of hand-held phones) was not elevated. There was a non-significant trend for tumors to be on the side of the head opposite to where the patients had reported using their phones. When Inskip et al analyzed tumors by histopathological type, there was no significant excess of any types of malignant or benign brain tumors (see figure below).
Brain Cancer in Cell Phone Users
(Inskip et al, 2001)
Relative risk of brain cancer (odds ratio with 95% confidence interval) in users of hand-held cell phones from the epidemiological study of Inskip et al. The number of cases in the overall analysis, and the sub-analyses are shown in parentheses. The phones used were "primarily analog".
The lines highlighted in red are probably the ones most relevant to cancer risk assessment as they look at long-term heavy use.
The line highlighted in blue refers to tumors in the lobe of the brain that should get the highest RF radiation exposure in users of hand-held phones.
The last 3 rows look at different histological types of brain tumors.
In early 2001, Johansen et al published a retrospective cohort study of all types of cancer in Danish cell phone users, some of whom has used cell phones as long as 5 years. This included 154 brain cancer patients. Cell phone use was associated with a significantly decreased overall risk of cancer that was attributable largely to less smoking-related cancer. No increased risk of brain cancer, leukemia, lymphoma, ocular cancer or melanoma was found in cell phone users. No significant increase in any types of cancer were found in cell phone users. No exposure response trends in leukemia or brain cancer incidence were seen in cell phone users. There was no increase in temporal or occipital lobe tumors in cell phone users. See figure below.
In the accompanying editorial Park wrote:
"Regardless of how convincing the evidence exonerating cell phones may be, there will continue to be those who will argue that the issue has not been completely settled. In science, few things ever are. The scientific community has a responsibility to put all the evidence in to perspective for the public."
Cancer in Cell Phone Users(Johansen et al, 2001)
Relative risk of cancer (odds ratio with 95% confidence interval) in users of hand-held cell phones from the epidemiological study of Johansen et al. The number of cases in the overall analysis, and the sub-analyses are shown in parentheses.
The line highlighted in red is probably the one most relevant to brain cancer risk assessment as it looks at long-term heavy use.
The line highlighted in blue refers to tumors in the lobe of the brain that should get the highest RF radiation exposure in users of hand-held phones.
The last 4 rows look at other types of cancer. In a study published in early 2000, Morgan and colleagues studied all major causes of mortality (with emphasis on brain cancer, lymphoma and leukemia) in employees of Motorola, a manufacturer of wireless communication products. Based on job titles, workers were classified into high, moderate, low, and background RF exposure groups. For workers with moderate or high RF radiation exposure no elevation in rates of brain cancer, leukemia and lymphoma were found. Actual peak and/or average RF radiation exposure levels are not known.
In January 2001, Stang et al reported that the use of "radio sets, mobile phones, or similar devices at [the] workplace for at least several hours per day" was associated with uveal (intraocular) melanoma. Of 118 individuals with intraocular melanoma, 6 (5.1%) reported that they were "probable or certain" to have "ever been exposed" to mobile phones at work. According to the authors, this occupational mobile phone use is 4 times higher than expected. Mobile phone use outside of work was not assessed, and other risk factors (for example, UV exposure and light skin color) were not assessed. In the only other comparable study, Johansen et al found less melanoma and ocular cancer than expected in cell phone users. According to the accompanying editorial:
Stang and colleagues raise that possibility that we should add a new type of cancer to those already under leading consideration as possible hazards of RF radiation, and it may well be that future studies will support their hypothesis. At this point , however, given the small size of the study, the relatively crude exposure assessment, the absence of attention to UVR exposure or other possible confounding variables, and limited support from the literature, a cautious interpretation of their results is indicated.
Summary of the epidemiology
The lack of associations between exposure to RF radiation and total cancer, and the lack of consistent associations between exposure to RF radiation and any specific type of cancer, suggests that RF radiation is unlikely to have a strong causal influence on cancer.
In a 1999 review of the RF epidemiology literature, Elwood concluded that:
Several positive associations suggesting an increased risk of some types of cancer in those who may have had greater exposure to RF emissions have been reported. However, the results are inconsistent: there is no type of cancer that has been consistently associated with RF exposures. The epidemiologic evidence falls short of the strength and consistency of evidence that is required to come to a reasonable conclusion that RF emissions are a likely cause of one or more types of human cancer. The evidence is weak in regard to its inconsistency, the design of the studies, the lack of detail on actual exposures, and the limitations of the studies in their ability to deal with other likely relevant factors. In some studies there may be biases in the data uses.
In a 2000 review of the RF epidemiology literature, Rothman concluded that:
Based on the epidemiological evidence available now, the main public health concern is clearly motor vehicle collisions, a behavioral effect rather than an effect of RF exposure as such. Neither the several studies of occupational exposure to RF nor the few of cellular telephone users offer any clear evidence of an association with brain tumors of other malignancies. Even if the studies in progress were to find large relative effects for brain cancer, the absolute increase in risk would probably be smaller than the risk stemming from motor vehicle collisions.
- Will mobile phone base station antennas affect medical devices such as cardiac pacemakers?
still working on.. few questions are still remaining
0 comments:
Post a Comment
Thanks for your Valuable comment