3. Can mobile phones cause cancer?
- 3.1 Have studies on mobile phone users revealed an increased cancer risk?
- 3.2 Have studies on laboratory animals revealed an increased cancer risk?
- 3.3 Have studies on cell cultures revealed genetic effects?
- 3.4 Discussion on cancer
3.1 Have studies on mobile phone users revealed an increased cancer risk?
More than 2 billion people use mobile phones worldwide Credit: Juha Blomberg
In 2007 and 2008, most studies on cancer in relation to mobile telephone use focused on brain tumours and other tumours in the head because exposure to radio frequency fields from mobile phones is concentrated in a small part of the head near the handset. Tumours investigated included notably a type of benign tumour of the inner ear known as acoustic neuroma and tumours of the salivary glands. A small number of studies investigated the link between exposure to radiofrequency fields from broadcast transmitters and tumour development.
In animal studies, where whole body exposure is sometimes assessed, other forms of cancer were also investigated. In vitro studies aimed to find out if biological effects relevant to cancer development can occur at exposure levels that are typical for mobile telephony.
Previous studies had found no increased risk of brain tumours among people who had been using mobile phones for up to 10 years. For longer duration of use, uncertainties remained as the number of such long-term mobile phone users was still small. Although none of the well-conducted studies indicated a substantial risk increase, they left the possibility open for a small-to-moderate risk increase among frequent mobile phone users, especially for glioma and acoustic neuroma.
The Interphone study, which has not yet been published, pools data from 13 countries and is coordinated by the International Agency for Research on Cancer (IARC). It involves case-control studies that compared the mobile phone use of a group of people with head tumours to that of a similar group who did not have such tumours. Results so far found no increased risk among people who had been using mobile phones for 10 years or more, neither for glioma nor meningioma nor tumours of the parotid gland.
Absorption of radiofrequency fields from mobile phones is concentrated in a small part of the head near the handset. In practice, whether the phone is preferably held to the right or the left side of the head will lead to a different exposure.
Case-control studies compare the mobile phone use of a group of people with head tumours to that of a similar “control group” without such tumours. When patients with a head tumour are asked about their preferred side of phone use, it may be difficult for them to remember and their answers might be biased by the fact that they know which side of their head is affected by the tumour. People in the control group, without such tumour, are less likely to be biased, since they do not know which side of their head will be relevant for analyses. This problem had already been identified in the very first such study which observed an increased tumour risk on the side that was said to be preferred and a decreased risk on the opposite side, whereas there should not have been a decrease in risk on the opposite side compared to the control group. That was found in one study, but there was, in that particular case, no correlation between an increase in exposure and an increase in risk on the preferred side. It remains unclear whether findings of studies reporting an increased risk of tumours on the preferred side are due to bias alone or also to actual effects.
A number of studies looked into the potential cancer risk of exposure to radio frequency fields from transmission towers. In most cases, no conclusions could be drawn, but some have shown an increased risk of leukaemia in children living close to strong radio or television broadcast transmitters. Two case control studies were recently completed in Korea (2007) and Germany (2008). The Korean study found an increased number of childhood leukemia cases in a 2 km radius of AM radio transmission towers, but no correlation was found between the estimated field strength and the increase in leukaemia. The German study observed no increased risk as a result of exposure from FM and AM transmission towers, during the decade prior to potential dilution from mobile telecommunication networks. More...
3.2 Have studies on laboratory animals revealed an increased cancer risk?
In the past, a number of studies on laboratory animals looked at the possibility of radio frequency (RF) energy causing cancer, and most found no causal link. One exception was a 1997 study that exposed a strain of mice prone to lymphoma to radio frequency signals similar to those transmitted by GSM-type handsets every day over 18 months. The researchers reported more new lymphoma cases among exposed mice.
Other researchers who carried out a similar experiment in 2002 found no significant effect on the number of new lymphoma cases in mice. Other studies had tested whether exposure to radio frequency fields alone could trigger any type of cancer in normal or genetically predisposed animals. Other studies have investigated whether exposure to RF fields could enhance the development of tumours triggered by cancer-causing chemicals, X-rays or UV radiation. No significant increase in the number of tumour cases has been reported among exposed laboratory animals, but most of these studies used relatively low exposure.
In the last few years, a number of lifetime and long-term exposure studies were performed on laboratory animals by exposing them to 900 MHz GSM signals and other higher frequency signals at higher exposure levels than previous studies. All studies concluded that there was no effect of radiofrequency fields on the risk of developing tumours even at the higher exposures. One study found a reduced survival rate in exposed animals, but this finding remains unexplained. More...
3.3 Have studies on cell cultures revealed genetic effects?
Scientists have studied a number of possible effects by exposing cell cultures to electromagnetic radiation in the radio frequency range (in-vitro studies). Most of the studies completed prior to 2007 did not provide evidence for any effect of radio frequency field exposure on isolated cells and tissues at an intensity level below the one that causes a warming effect.
One study found that the exposure increased DNA damage in connective tissue cells (fibroblasts), but not in white blood cells (lymphocytes). However, the scientific validity of this study is unclear, making any interpretation of the results difficult at this point.
Another study found changes in the number of certain chromosomes (missing or extra chromosomes) in human white blood cells.
Studies of other cell components have provided mixed results of increases in the activity of certain enzymes, in the presence of free radicals, and the onset of cellular decay. However, there is little agreement between studies, and the health significance of the effects observed remains unclear. More...
3.4 Discussion on cancer
Studies on users that have had mobile phones for less than ten years indicate no increased risk of developing a brain tumour.
However, due to the relatively recent introduction of mobile phone technology and subsequent widespread use, it is difficult to investigate the risks associated with long-term use through studies on human populations. Few users have had mobile phones for more than ten years.
This prevents firm conclusions related to the use of mobile phones beyond 10 years, as only a few such long term users have been included in studies on cancer. Moreover, estimates of past exposures are uncertain and finding representative study participants is difficult.
The new data released in the last few years have not ruled out the existence of a small cancer risk increase. The data from the complete Interphone study, which should be published in 2009 could shed light on the remaining uncertainties.
Recent studies on human populations provide evidence against an association between exposure to radiofrequency fields from broadcast transmitters and the risk of childhood leukaemia. Exposure from new sources such as mobile phone base stations, cordless phone base stations or wireless networks is generally lower than the ones investigated in studies on radio broadcast towers. Thus, there appears to be no immediate need for further studies related to these sources. However, studies on mobile and cordless phone use among children and adolescents are still completely lacking.
Overall, the results of the new studies are consistent with results from previous studies, and add to the evidence that the radiofrequency fields such as those emitted by mobile phones are not carcinogenic in laboratory rodents.
Different biological effects have been investigated in cell cultures exposed to radiofrequency fields, using a variety of cell types and exposure conditions with diverse outcome. For radio frequency fields that led to an energy absorption below the recommended safety limit for the head (2 W per kg of tissue), in vitro studies have not identified reproducible effects by which carcinogenicity in living systems could be explained. More...