Intended for healthcare professionals


The health hazards of mobile phones

BMJ 2000; 320 doi: (Published 13 May 2000) Cite this as: BMJ 2000;320:1288

The only established risk is of using one while driving

  1. Michael Maier, senior lecturer (Michael.Maier{at},
  2. Colin Blakemore, professor (blakemore{at},
  3. Mika Koivisto, researcher (mika.koivisto{at}
  1. Division of Neuroscience and Psychological Medicine, Imperial College School of Medicine, London W6 8RP
  2. Laboratory of Physiology, University of Oxford, Oxford OX1 3PT
  3. Centre for Cognitive Neuroscience, University of Turku, 20014 Turku, Finland

    Despite repeated horror stories about mobile phones in the media, nearly half of the British public now owns one. Some 500 million people worldwide use mobile phones. Clearly, they have decided that the benefits outweigh any risks to their health. The benefits to the Exchequer in the United Kingdom are also substantial—£22bn ($13.75bn)from the recent round of bids for new licences. In this context, the publication of the Report of the Independent Expert Group on Mobile Phones, a group organised by the Department of Health, could have political implications.

    Mobile phones are low power radio devices that transmit and receive radio frequency radiation (at frequencies in the microwave range of 900-1800 MHz) through an antenna used close to the user's head. Digital systems have recently replaced analogue. There is concern that microwaves might induce or promote cancer, and the symptoms associated with their use include sleep disturbance, memory problems, headaches, nausea, and dizziness.1 Changes in the permeability of the blood-brain barrier, electroencephalographic activity, and blood pressure have also been reported.2 The validity of many of these findings is uncertain, as are the mechanisms for such actions. Even so, rather than dismiss such concerns, the report says that there is sufficient anecdotal evidence to justify further research and taking a precautionary approach to the use of mobile phones.

    UK guidelines are set by the National Radiological Protection Board and are based on the assumption that the only risk from microwave radiation arises from thermal effects—that is, from the heating of tissue that it can induce. Today's mobile phones, with a total power output of about 1 W, are estimated to produce insignificant local heating (equivalent to about a 0.1°C rise in temperature in the brain), which is unlikely to produce any deleterious effects. Although the recommended limits of exposure are similar in the United States and western Europe, there is no global consensus. Limits are stricter in some countries, especially Russia, where early research (albeit largely inadequately documented) led to concerns that microwave radiation too weak to cause serious amounts of heating might still pose risks to living systems.

    Recent research from many countries suggests, however, that there are “non-thermal” effects on living tissue, ranging from immediate early gene expression and micronucleus formation to changes in the excitability of nerve cells, permeability of the blood-brain barrier, and the ability of rats to learn mazes.

    Limits on exposure for workers have been suggested by the International Commission on Non-Ionizing Radiation Protection and are similar to those set by the National Radiological Protection Board. However, the commission recommended that the limit for the general public should be five times lower to provide additional protection for those who are ill or very young, since these groups may be more vulnerable. In the absence of stronger evidence that there is no risk from mobile phones, the recommendation of the independent group that these guidelines for public exposure should be adopted is prudent. So too are the report's recommendations to minimise power output and label phones with power ratings.

    This is a controversial field of science. In vitro experiments on cell proliferation, membrane properties, and ion channels are difficult to extrapolate to humans. Moreover, it is also difficult to extrapolate effects on brain function and behaviour from rodents to humans because the entire brain of a rat or mouse is exposed but for a person using a mobile phone only the small region of the head that is close to the phone would be exposed. Although some studies have claimed to show an increase in DNA strand breaks in rats, others have failed to replicate this finding.35 Concern was raised by the findings by Repacholi and colleagues of an increase in lymphomas occurring in transgenic mice that were prone to developing tumours and that had been exposed to microwave radiation for 18 months.6 This work is now being repeated. The greatest mystery about non-thermal effects is their lack of a theoretical basis. Biological systems might interact resonantly with microwave fields but there is as yet no robust evidence.7

    So far there is no clear evidence from epidemiological studies of a relation between mobile phone use and mortality or morbidity.8 Tantalising findings in humans include a speeding up of reaction time during exposure, particularly during behavioural tasks calling for attention, and electroencephalographic changes during cognitive processes.912 It is not clear, however, whether these findings have implications for health.

    The only established health hazard cited by the independent group comes from the use of mobile phones while driving. The risk of an accident increases with age and is equivalent (when braking times are measured) to a blood alcohol level of 0.05%. The risk is the same when the phone is used “hands free” (via a loudspeaker), implying that it is due to the distraction caused by the conversation.

    There are undeniable benefits in carrying mobile phones in vehicles: many lives have been saved by rapid reports of cardiac arrest and of serious trauma.13 But the independent group's report is clear that even hands free mobile phones should not be used while driving.

    Mobile phones have changed the way people work and communicate. But this independent group's report is right to recommend precautionary measures to encourage both manufacturers and users to limit microwave exposure until we can be more confident that the use of mobile phones is indubitably safe.


    Colin Blakemore is a member of the independent expert group on mobile phones. Mika Koivisto has worked on an independent research project examining the effects of mobile phones on brain function. This research was funded by Nokia, a manufacturer of mobile phones.


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