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?
3.1 Have studies on mobile phone users revealed an increased cancer risk?
More than 2 billion people use mobile phones worldwide
Credit: Juha Blomberg
Research indicates that a person who has used a mobile phone for up to 10 years does not have a higher risk of brain tumours or other cancers in the skull. This also appears to be the case for someone who has used a mobile phone for more than 10 years but more research is needed to confirm this.
In 2001, few studies were available on exposure to radio frequency fields from mobile phones and transmitters, and those had serious shortcomings. Since then, there have been about 30 studies on mobile phone use and cancer. Most of the recent studies have focused on brain tumours and other tumours in the head because the energy generated by radio frequency signals is concentrated in a small part of the head near the handset.
The largest study followed hundreds of thousands of Danish mobile phone subscribers for up to 21 years. The study, which looked at a variety of cancers, found no increased risk among people who had been using mobile phones for 10 years or more.
All other studies were case-control studies, meaning they 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. Several were conducted as part of the Interphone programme, which pools data from 13 countries and is coordinated by the International Agency for Research on Cancer (IARC).
Results from four countries participating in this programme – Sweden, Denmark, the United Kingdom and Germany – suggest no increased risk of two types of brain tumours (meningioma and glioma) that have been suspected to be linked to mobile phone use. However, a Swedish group not participating in the Interphone programme has repeatedly found increased risks for brain tumours. In 2006, the group reported statistically significant risk increases for both analogue and digital mobile phones as well as cordless phones after just one year of use. The relative risk estimates doubled after 10 years of mobile phone use. This research group also found an increased risk for a type of benign tumour of the inner ear known as acoustic neuroma.
Three countries in the Interphone study – Denmark, Sweden, and Japan – have reported their acoustic neuroma results. Sweden estimated that people who routinely use mobile phones for 10 years are twice as likely to develop acoustic neuroma as those who seldom use mobile phones. The study suggested an even stronger link between preferred mobile phone use on one side of the head and an increased risk of acoustic neuroma on that side of the head. The results from Denmark and Japan, which were based on fewer long-term users, did not support this.
Five of 13 countries in the Interphone study (including Denmark, Finland, Norway, Sweden, and the United Kingdom) pooled their results on the risk of acoustic neuroma. Long-term mobile phone use in itself did not appear to increase a person’s risk for acoustic neuroma in general. But the data suggested that long term mobile phone use on one side of the head may increase a person’s risk for these tumours on that side of the head.
All these studies faced limitations because the exposure was determined either on the basis of a list of subscribers provided by the operators or on self-reported mobile phone use. More...
3.2 Have studies on laboratory animals revealed an increased cancer risk?
Previously a number of studies on laboratory animals looked at the possibility of radio frequency 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 daily doses of radio frequency signals similar to those transmitted by GSM-type handsets during 18 months. The researchers reported that the number of new lymphoma cases among exposed mice was twice that of non-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. One difference between the two experiments was the mode of exposure. In the 2002 study the exposure was one hour a day five days a week, whereas in the 1997 study it was 30 minutes twice a day, seven days a week.
Other studies have 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. More...
3.3 Have studies on cell cultures revealed genetic effects?
In 2001, scientists had studied a number of possible effects by exposing cell cultures to electromagnetic radiation in the radio frequency range (in-vitro studies). Much of this research looked for damage to the cell’s genetic material, and some reports indicated such genotoxic effects.
Additional types of cell cultures have since been studied, mostly focussing on effects of short-term exposure. Overall, the studies show little evidence of health-relevant effects when exposure is below existing safety guidelines. But some studies suggest gene expression is affected at exposure close to guidelines.
It is generally accepted that radio frequency fields do not directly damage DNA because they are not powerful enough to break chemical bonds (ionize). However, it is possible that when cellular constituents are altered by exposure to electromagnetic fields, DNA could be indirectly affected.
One study by 12 research groups in seven European countries looked at EMF effects at cellular and sub-cellular levels. In 2005, one of the groups in this so-called REFLEX study reported effects on chromosomal content, including DNA strand breaks in certain kinds of human and rat cells after RF exposure. But a subsequent study failed to reproduce these results.
As for other effects on cells unrelated to genetic change, several studies researched how RF fields affect cell proliferation but most detected no effect. Other studies have addressed whether RF fields can cause programmed cell death (apoptosis), which is when cells start dying in response to mild damaging stimuli. Apoptosis is an important protection mechanism against cancer as it removes potential tumour cells. No difference was detected compared with normal cells not exposed to RF fields. While one study suggested that abnormal leukemia cells survived longer if exposed to RF fields, another found that exposure could induce apoptosis in skin cancer cells.
The REFLEX study looked at various aspects of cellular life and reported no effects of RF fields on cell proliferation, cell differentiation, programmed cell death, DNA synthesis, and the functioning of immune cells. Some studies showed changes in gene expression for different RF exposure conditions and different cell types.
Some researchers have found increased levels of heat-shock proteins after RF field exposure. These important proteins eliminate other proteins that appear when a cell is under stress from temperature or other external factors. However, the increased levels have not been confirmed by other studies. In particular, one of the research groups that initially reported increased heat-shock protein levels has been unable to reproduce those results. More...