The Electric Field

The electric field mainly causes effects on the body surface. It penetrates only slightly into the human body. Biological tissue, such as, e.g., the human body, to a high degree consists of conductive liquids and organic tissues. If an external electric field interferes with a person, field forces affect the electrically charged particles in the body and can redistribute them. The result is the induction of currents in the body. This process – called electrostatic induction – occurs until the body surface is uniformly charged and no electric field exists in the interior of the body.

In the case of time-varying fields the redistribution of electric charges is permanently repeated according to the frequency. Currents in the body are induced following the same frequency. As a consequence of the low field strength occurring in every day life the currents induced by the electric fields are also very low.

Humans can perceive electric fields above a threshold which is modulated by inter-individual differences. Small hairs on the body surface vibrate in the time-varying electric field. The frequency of the vibrations is identical with that of the electrical field.

Besides these direct effects some indirect effects of electric fields are known such as, e.g., transient discharges and contact currents. They are caused by differences of the electric potential between charged objects and the affected person. Differences of the electric potential are neutralised if the human body gets into a conducting contact with such objects. The resulting contact currents can be perceived if they are above a specific intensity. Many people receive an electric shock when touching a doorknob or walking on certain carpets. In such a case charges of the doorknob or the carpet are different from that of the skin surface. The difference of the electric potential is neutralised by sparking. Thereby a very high current density can occur for a short time.

In every day life such contact currents are usually harmless and do not present a health hazard even when interfering for a long time. Under the influence of very strong electric fields, however, very uncomfortable and painful transient discharges can occur. Such cases are rare; they may occur if, e.g., large metal surfaces below high voltage power lines are isolated from ground.

The Magnetic Field

In contrast to time-varying electric fields time-varying magnetic fields directly produce circulating electric currents in the interior of the body as a consequence of magnetic induction.

The dominant quantity for the evaluation of a possible health impact is the density of the current in the body. It is reported as milliampere per square meter (mA/m²).

Even without external fields electric currents occur in the human body. Nerves transmit their signals via electric pulses. The heart is electrically active, too – this can be demonstrated by means of an electrocardiogram (ECG). Nearly all metabolic processes are accompanied by a displacement of charged particles (ions). The naturally occurring current densities are in the range of 1 to 10 mA/m².

If additional currents are induced in the body biological effects occur above a certain threshold value, and health hazards may occur with higher currents. The basic mechanism is the stimulation of nerves which can even provoke cardiac fibrillation and additional heart contractions.

The internationally recommended basic limits for low frequency electric and magnetic fields are based on the naturally occurring current densities in the body and on threshold values for established health effects: a basic limit of 2 mA/m² has been defined for induced current density in the body.

Cardiac pacemakers and other electronic implants may be influenced by electric and magnetic fields below the limit values. The susceptibility of pacemakers and other implants depends on the type of implantation, the programmed sensibility and the type of device. The danger level of an interference has to be assessed for each individual case by the physician in charge.

For older types of pacemakers an interference with their functionality is possible at an electric field strength of as low as 2.5 kilovolt per meter (kV/m) or a magnetic flux density of 20 microtesla (µT).

The consequences for affected persons are difficult to predict. Normally the pacemaker should recognise any interference from outside and should switch to a secure mode. Sometimes, however, uncomfortable irregular heartbeats may occur. Even life-threatening situations cannot be excluded completely. Therefore, affected persons should avoid strong fields. Please contact your physician in case of doubt!

In homes, a distance of some 30 cm from household equipment gives sufficient protection.

While the acute effects of low frequency fields described above are scientifically established, considerable uncertainties exist on possible long-term effects and biological effects at field intensities below the limit values. These effects have been subject to scientific investigation for some time. Among others, effects of low frequency fields on the cellular membrane, the metabolism of hormones, activities of enzymes, DNA-synthesis and certain biological messengers have been reported. Even an effect on tumour growth cannot be excluded. In many cases the reported biological effects could not be reproduced by subsequent investigations. Extrapolation of biological effects found in cell or animal experiments to human beings and the relevance of effects to human health has not been clarified in many cases.

Since the end of the seventies of the last century a possible association between low frequency, low intensity fields and cancer has been examined in epidemiological studies. In adults no elevated risk of cancer due to a long-lasting exposure to low frequency fields was found.

The situation is different for leukaemia among children. In some epidemiological studies a slightly but significantly elevated risk of leukaemia was found in children exposed for relatively long time to magnetic fields which were well below the limit value. A corresponding study in the Federal Republic of Germany showed that exposure during night time seems to play a special role. The height of exposure above which the elevated leukaemia risk has been observed is, however, in the upper level of exposure measured in German households. The study states that up to 1 % of leukaemia cases among children could be explained by an elevated exposure to low frequency magnetic fields, if a causal relationship should definitely exist (final report of the study in German). As with all epidemiological studies a cause-effect-relationship cannot be proven by a statistical association. So far a biological mechanism that would explain how low frequency magnetic fields could initiate leukaemia or promote the growth of leukaemia cells is not known. Several factors are involved in the induction of childhood leukaemia. Their interaction is not yet understood. Moreover relevant risk factors for leukaemia in children are possibly still unknown so that they could not be considered when evaluating the data. On the basis of the epidemiological evidence the International Agency for Research on Cancer (IARC) classified low frequency magnetic fields in 2002 as "possibly carcinogenic to humans". This classification was confirmed by WHO after reviewing again all available scientific data in 2007 and despite the still missing information on possible mechanisms. Therefore the potential risk for children due to low frequency magnetic fields has to be taken seriously. Precautionary measures are indicated.

Electrosensitivity

Approximately two percent of the German population claim to be electrosensitive, i.e., they attribute various complaints such as, e.g., headache, sleep disturbances, fatigue, concentration disorders etc. to the existence of electromagnetic fields in their surroundings. For a long time the complaints were mainly related to low frequency electric and magnetic fields but since the rapid extension of mobile phone networks, the blame is also put on high frequency fields. In several scientific studies (e.g. within the German Mobile Telecommunication Research Programme) the phenomenon “electrosensitivity” has been examined mainly with the aim to make the complaints more clear and to better understand the possible causal relationship between electromagnetic fields and adverse health effects. Up to now there is not enough scientific evidence available to establish such a causal relationship. It could be shown by the German Mobile Telecommunication Research Programme that electrosensitive persons can be characterised by a reduced capability to discriminate a sham from a real magnetic pulse. Shielding of high frequency electromagnetic fields in the subjects' bedrooms did not improve their sleep quality. However their subjective sleep behaviour improved when they believed that they were shielded. However measurable objective sleeping parameters did not support the subjective reports. The relationship to an accumulation of allergies and/or a special sensitivity to chemicals which is often claimed by the affected persons could not be confirmed.