Number of US cell phone subscribers by year (data source: Cellular Telecommunications Industry Association, 2007). 

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... of cell phone systems, or “ 2G. ” Mass deployment was present in most countries from the mid 1990s ( Fig. 1). The latest system currently in mass deployment is based on adaptations of CDMA and TDMA (800 and 1900 MHz; “ 3G ” ). Radio waves emitted by modern GSM handsets have a peak power of 1 to 2 W, whereas other digital cellular technologies have power outputs of below 1 W, levels generally regarded as being safe by international regulatory authorities. The 3G has less than 0.25 W of peak power. Through “ adaptive power control, ” the power generated by a cell phone can vary during a conversation according to the amount of interference with the signal, for example, due to the user being in a moving vehicle or within a building or elevator. The output power of the phone is generally set to the highest level during “ handovers ” between networked base stations as a user moves from one geographic area to another or when signal interference is greatest. The output power of the new 3G is measured for small cells to be, on the average, 0.25 mW, and in a larger cell, about 12 mW. It should be noted that cordless phones operate as transmitters and receivers like GSM cell phones despite shorter signal distances to the home desktop base station. Although such phones have lower peak power than cell phones, user call times tend to be longer. Furthermore, because of adaptive power control of cell phones, the average power output of cordless phones is comparable to cell phones at least in urban areas. Cell phone base stations or masts emit EMR continuously and at far greater power than cell phones which emit EMR continuously only during calls. Between calls or “ at rest ” with the “ screen asleep ” but the power on, cell phones emit a regular pulse of EMR in order for base stations to continuously keep track of the geographic position of the phones in their “ cellular network. ” The GSM antennae are associated with transmitter powers of 10 to 100 W, although 3G antennae use less power — on average 3 W in urban areas. In rural areas, base station power output is much higher because of the vast areas requiring coverage between sparsely distributed base stations, and cell phones rurally are more often at their maximum power output during use in order to maintain good communication [13,37]. Overall, the number of towers has increased tremendously in the past decade and smaller, but even more numerous “ microcell ” antennae throughout metropolitan environments now enable clear cell phone reception within previously reception-poor locations such as in elevators and building basements. An EMF is composed of an electric field generated by differences in voltage and a magnetic field generated by the flow of current. The field propagates at the speed of light in waves of a certain length that oscillate at a certain frequency. In the electromagnetic range, gamma rays given off by radioactive materials, cosmic rays, and x-rays are all dangerous to humans and other organisms because of the relatively high-energy “ quanta ” they carry via high- frequency or short-wavelength waves. Such rays lead to dangerous “ ionizing ” radiation with an ability to break intermolecular bonds. Cell phone systems also act via EMR but in the microwave or radiofrequency range close to that of a microwave oven (although cell phone power output is much less). These systems are supposedly safe because of the lower-energy quanta they carry via relatively low- frequency or long-wavelength waves, that is “ nonionizing ” owing to insufficient energy to break intermolecular bonds. This notion, however, has been contested in the scientific literature [27,28,38] and, as detailed below, has led to concerns regarding nonthermal rather than thermal (direct tissue heating) effects of cell phone – related EMR on cells and tissue systems within the near-field of the antenna. The intensity of EMR (power density) varies with the distance from the source according to the inverse square law. The SAR measures the rate at which radiation is absorbed by the human body and is therefore relevant to “ exposure. ” For the head, the FCC has set an acceptable SAR of 1.6 W/kg. In cellular telephony, the SAR depends on several factors, including the antenna type and position, head morphology, the distance between the phone and the head, and the power output of the phone that can vary [3,13]. Exposure of the brain depends on the type of phone and position of the antenna [3] but tends to be highest in the temporal lobe and insular region and overlying skull, scalp, and parotid gland tissues. Irrespective of the type of phone, exposure is highest on the side of the head against which the cell phone is held [3] and appears to be even higher in children owing to thinner scalps and skulls, increased water content of their brain, and lower brain volume [26,65]. There are currently over 3 billion cell phone users globally, with developed nations already approaching the saturation point (Fig. 2). Users starting as young as 3 years of age are expected to be exposed to near-field cell phone EMR for their entire lifetimes. There has been much controversy regarding health risks associated with cell phones, with confusion partly arising from the relatively short length of participant follow-up in most of the published epidemiologic studies. In studies testing any association between long-term (ie, ≥ 10-year) cell phone use and brain tumor development, the three groups of brain tumors assessed are glioma (specifically, astrocytoma), acoustic neuroma, and meningioma. In this section, the authors focus on all the currently published peer-reviewed epidemiologic studies that have attempted to address whether 10 or more years of cell phone use is associated with the development of intracranial tumors on the same side of the head (ipsilateral) as that preferred for cell phone usage (ie, all long-term studies with a “ laterality analysis ” ). In order to be included in the present meta-analysis, studies were required to have met all of the following criteria: (i) publication in a peer-reviewed journal; (ii) inclusion of participants using cell phones for 10 or more years (ie, minimum 10-year latency); and (iii) incorporation of a laterality analysis of long-term ( ≥ 10-year) users. The PubMed database was comprehensively searched up to December 1, 2008, using terms including mobile phone , cell phone , brain tumor , neoplasm , incidence , acoustic neuroma , meningioma , glioma , and astrocytoma . If a study had more than one publication on certain epidemiologic aspects, the latest publication giving the most relevant data was used. The present analyses are based on the adjusted ORs in the different studies. It should be reiterated that participant overlap (redundancy) has been avoided in the present meta- analysis by the appropriate handling of pooled versus individual INTERPHONE publications where individual national data sets were available. Furthermore, there is no overlap of participants in the 2 pooled studies of Hardell [14,18], as well as no overlap in participants between the Swedish studies of Hardell [14,18] and the Swedish arm of INTERPHONE [29,30,35,36] since persons from different parts of Sweden were included in those 2 groups of studies. The present statistical analysis was carried out using a fixed- effects model based on the case-control design of all of the included studies (Stata/SE 10.1 for Windows; StataCorp, College Station, Tex). To the authors' knowledge, there are only 11 published studies examining long-term cell phone use (ie, use for ≥ 10 years) and the risk of developing a brain tumor [8,9,14,18,23,29,30,35,36,54,55] (Table 1). These 11 studies fall into two distinct streams of data, namely, (i) the “ Hardell group ” studies [14,18] from Sweden that were the first case- control studies to report an association between the use of cellular and cordless phones and brain tumors [16] and (ii) the “ INTERPHONE group ” studies [8,9,23,29,30,35,36,54,55] authored by researchers of the multinational INTERPHONE consortium (see below). The Hardell studies are comprehensive case-control studies looking at data exclusively from Sweden acquired between 1997 and 2003, whereas the INTERPHONE study is a multinational collective of several comprehensive case- control studies looking at data acquired between 1999 and 2004. Detailed reviews of the methodological aspects of these two data streams, including their limitations pertaining to the extent of subject participation and selection and recall biases, are given elsewhere [4,15,63]. The studies incorporate thousands of cases and controls, although notably far fewer using cell phones for 10 or more years (Table 1), and are briefly summarized below. Since the latter half of the 1990s, Lennart Hardell and his colleagues from Sweden have performed six case-control studies in the area of cellular and cordless phones and tumors [19]. Three of the studies concerned brain tumors; one, salivary gland tumors; one, NHL; and one, testicular cancer. Exposure was assessed by detailed self-administered questionnaires. The Hardell brain tumor studies had approximately 90% case and control participation rates, with cases (n = 2158 participants) and controls (n = 2162 participants) identified from Swedish cancer and population registries, respectively [14]. Pooled analyses of their results regarding brain tumors are incorporated in the present review. In brief, significantly elevated risks of developing an ipsilateral astrocytoma and acoustic neuroma were found in analogue and digital cell phone and cordless phone users. The OR increased with latency period, particularly more than 10 years, and with cumulative cell phone use more than 2000 hours. Higher ORs were calculated for WHO grade III and IV astrocytomas than for WHO grade I and II astrocytomas. No association was found with salivary gland tumors, NHL, or testicular cancer, but fewer persons in ...

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... are currently over 3 billion cell phone users globally, with developed nations already approaching the saturation point (Fig. 2). Users starting as young as 3 years of age are expected to be exposed to near-field cell phone EMR for their entire lifetimes. There has been much controversy regarding health risks associated with cell phones, with confusion partly arising from the relatively short length of participant follow-up in most of the published epidemiologic ...