Electromagnetic Radiation from the Electricity Grid and Leukemia in Children

Leukemia is a malignant disease (tumor) of the blood and immune systems.  It is relatively rare, but among the cancers appearing in childhood it is the most prevalent.  In Israel in 2006 leukemia constituted 22.4% of all cancers in children and adolescents up to the age of 19 years.

 

Among all the types of childhood leukemia, acute lymphocytic leukemia (ALL) constitutes 78%, while acute myelogenous (myeloid) leukemia (AML) accounts for 15%. Most cases of acute lymphocytic leukemia manifest themselves at age 2-4, while acute myelogenous leukemia may manifest itself at any period during childhood and adolescence, although it is most prevalent before two years of age and during adolescence.

White blood cells

 

The causes for the development of leukemia are unknown, but some researchers attribute it to genetic factors and various environmental factors, including radiation from extremely low frequency magnetic fields.

 

Extremely low frequency (ELF) radiation and development of leukemia in children: early observations

In 1979 Nancy Wertheimer and Ed Leeper reported finding an increased risk for developing leukemia among children up to 19 years of age in whose homes a relatively strong electric current had been measured. They associated this observation to the magnetic fields created by the electric current.  Following this finding, additional studies were conducted in various countries, to investigate the association between ELF magnetic fields (50/60Hz) and the incidence of childhood leukemia.

 

 Residential electromagnetic fields

The levels of the electric and magnetic fields inside the home depend on a number of factors, including the distance from power lines, as well as the type of wiring and their location, and the types and number of electrical appliances in the home.  The strength of the magnetic field surrounding an electrical appliance depends on its voltage and the strength of the electric current, as well as on the shape of the appliance.  The household appliances that produce the strongest magnetic fields are those with a strong electric current or a high-revolution motor (e.g. vacuum cleaners, dishwashers, washing machines, food processors and electric shavers).  The strength of the magnetic field decreases with increasing distance from the appliance.

 

Magnetic fields are not blocked by common materials such as the walls of buildings. The strength of an electric field, on the other hand, decreases significantly when passing through walls. Therefore, there is no correlation between the levels of radiation from the electric and magnetic fields inside the home.  If the home is situated in proximity to high-voltage power lines, for example, the level of radiation from the magnetic field will be relatively higher than that of the electric field. 

 

High voltage power lines near residences

High voltage power lines near residences

 

From early studies up to the IARC resolution

Most epidemiological studies that investigated the association between exposure to magnetic fields in proximity to residences and the risk of developing childhood leukemia focused on exposure to high-voltage power lines.

 

These were case-control studies that collected data on children from defined age-groups (e.g. 0-15 years) diagnosed with leukemia – the 'case group' – and on children in the same age-group with similar demographic characteristics that were not afflicted – 'control group'. The level of exposure of the two groups to magnetic fields – during a predetermined period of time – was determined  by the distance of the residence to the power lines and/or by characterizing the type of magnetic field or by measurements made on site (for a more detailed description see methods of evaluating the level of exposure to a magnetic field).  After collecting the data the researchers compared the strength of the magnetic fields to which the 'case group' (children who suffered from leukemia) had been exposed, to the strength of the magnetic fields to which the children in the 'control group' (not afflicted) had been exposed.  In case-control studies the index for understanding the results is the odds ratio.

 

 

   

 

Most humans are exposed in one way or another to magnetic fields emanating from the electric grid, so that there is no practical possibility of comparing an exposed population to one that was never exposed to this source of radiation.  Hence, in order to distinguish between different levels of exposure, most studies that investigate a possible association between exposure to residential magnetic fields  and the risk of developing childhood leukemia divided the strength of the magnetic field into categories of exposure (e.g. 0.1-<0.2 microtesla, 0.2-<0.3 microtesla, 0.3-<0.4 microtesla, and 0.4 microtesla).  The lowest category of exposure (< 0.1 microtesla) served as basis for comparing with all the other exposure levels.

 

It is important to remember that the division into different exposure levels is a technical one, and has no biological basis whatsoever.  Moreover, it should be noted that a relatively low proportion of individuals is exposed to a level higher than 0.4 microtesla.  According to studies conducted in various countries, only 4-5% of the population is exposed to an average level higher than 0.3 microtesla, and only 1-2% to a level higher than 0.4 microtesla.  Thus, the highest category is determined for practical purposes and should not be considered as reflecting the level from which the actual risk begins.

 

  

 

In 2000 two pooled analyses of case-control studies were published.  One pooled analysis summarized the data from nine different studies, and the other  summarized the data from twelve studies. Although all of these were case-control studies, the assessment of exposure to magnetic fields was performed by different methods – measurements in homes and/or magnetic field calculations. The results of both pooled analyses indicated that prolonged exposure to relatively high levels of magnetic fields (above 0.3-0.4 microtesla – equivalent to 3-4 milligauss) increases the risk of developing childhood leukemia by a factor of 1.5-2.

 

In 2001, on the basis of population studies of this topic published until 1999, the International Agency for Research on Cancer (IARC) categorized extremely low frequency magnetic fields as possibly carcinogenic to humans (category 2B).

 

It should be noted that most experimental studies conducted on tissue cultures or laboratory animal models failed to confirm this association.  Moreover, to date no proven biophysical mechanism has been found that could unequivocally explain the association observed in the population studies described above.

 

 
   

 

In residences in proximity to high voltage power lines, the magnetic field originates mainly from the power line.  However, in most countries the number of residences situated in proximity to high voltage power lines is minimal.

 

According to data from the Israeli Ministry for Environmental Protection, the average exposure to a magnetic field originating from the electric grid does not exceed 1 milligauss (0.1 microtesla) in the majority of residences in Israel and abroad.

 

 

Later studies

The findings of follow-up studies published after the IARC resolution, as well as pooled analyses of population studies published subsequently, confirmed the previous findings, and also supported the existence of an association between exposure to magnetic fields originating from high-voltage power lines and the risk of developing leukemia in childhood.  The report of a World Health Organization Working Group (Environmental Health Criteria) published in 2007, and reviews by the European Commission published in 2009 and updated in 2015 – SCENIHR – (pdf document available for downloading), and in 2012 – EHFRAN – (pdf document available for downloading), strengthened the validity of the previous conclusions of the IARC.

 

In 2005 the findings of a case-control study conducted in England and Wales were published.  This study investigated whether living in proximity to high-voltage power lines influences the risk of developing childhood cancer.  In this study the researchers used the residential address of the mother at the time of giving birth as a measure for exposure to magnetic fields emanating from power lines, and investigated the possible association between distance of the home from the high-voltage power line and the risk of developing childhood leukemia.  The study comprised 30,000 children up to 14 years of age diagnosed with cancer between the years 1965-1995 (over a period of 30 years) and a similar number of healthy children matched by sex, date of birth, and mother's residence at childbirth.  The findings indicated an increased risk of 69% (95% confidence interval 1.13-2.53) for developing leukemia in children whose residential address at the time of birth was within 200 meters from high-voltage power lines, compared to children who lived 600 meters or more from the high-voltage power lines.

 

A later case-control study, published in 2014, conducted by the same British researchers re-examined the issue. This time the sample included a higher number of childhood leukemia cases (53,515) in children and adolescents up to 15 years of age collected throughout Britain over the years 1962-2009 (46 years) – i.e. a longer period of time.  In this study too the distance of the mother's residence from the electric power lines at the time of childbirth served as a measure for the level of exposure to magnetic fields.  However, in contrast to the previous study, the results of this study did not indicate an increased risk of developing childhood leukemia among children who lived in proximity to power lines at the time of birth.  One of the interesting findings was that data analyzed by decades indicated that during the years 1960-1980 there was an increased risk of developing leukemia among children who lived up to 600 meters from high-voltage power lines of 275 or 400 kV, while children who lived more than 1000 meters from power lines of the same voltage did not manifest an increased risk.  During later decades data analysis did not indicate an increased risk of developing leukemia among children who lived up to 600 meters from the power lines.  The researchers suggested that the difference in findings between the first decades and the last two could be explained by changes in the characteristics of the population that resided in proximity to the power lines. The same researchers also performed a similar analysis using the same data while focusing on the magnetic fields of high-voltage underground cables. They did not find indications of an association of risk for childhood leukemia with distance from the child's residence or of trend in risk with increasing magnetic field.  

 

Another case-control study, conducted in France during the years 2002-2007, comprised 2779 children up to 14 years of age diagnosed with leukemia, and 30.000 children in the control group.  This study indicated a higher risk (not statistically significant) for children who lived 0-50 meters from high-voltage power lines (225 or 400 kV) compared with children who lived more than 50 meters from power lines of similar voltage.  No increased risk was detected among children who lived close to power lines of lower voltage (63-150 kV).

 

In an additional case-control study conducted in Denmark during 1968-2000 (38 years), data were collected on 1698 children diagnosed with leukemia and 3396 healthy children in the same age-group.  In this study too the exposure level was assessed according to the distance of the children's residences from the power lines in the year of birth.  The results showed no increased risk of developing leukemia among children who lived up to 600 meters from power lines with a voltage of 132-400 kV.  When the data analysis focused on children who lived close to power lines with a voltage of 200 or 400 kV, an increased risk of developing leukemia (not statistically significant) was revealed in children who lived 200-600 meters from these power lines (compared with those who lived more than 600 meters from them); the researchers claimed that this finding might be incidental.

 

In 2014 a meta-analysis of nine case-control population studies was published, comprising studies conducted in seven countries, the results of which were published between 1997 and 2013.  The meta-analysis comprised data on 11,699 children aged 0-15 years diagnosed with leukemia, and 13,194 healthy children in the same age group (controls).  The data were collected over a period of 45 years (1962-2007) in the different case-control studies.  In the quantitative conclusion of the meta-analysis it was found that there was a 2.4-fold increase in the risk of developing acute lymphocytic leukemia (ALL) among children exposed to magnetic field radiation of 0.4 micro-tesla or more in the vicinity of their residences, compared with children exposed to radiation lower than 0.1 micro-tesla (95% confidence interval 1.30-4.55).

 

Summary

Despite the evidence presented above, most of which points to an increased risk of developing leukemia in children who lived close to high-voltage power lines, a causal relationship has not yet been proven, between exposure to magnetic fields emanating from high-voltage power lines and the risk of developing childhood leukemia.  In order to prove a causal relationship between an exposure factor and the risk of developing a disease, one must consider additional criteria, such as those outlined by Austin Bradford Hill for determination of a causality.

 

In any case, most researchers today posit that the attributable risk of developing leukemia following exposure to magnetic fields emanating from power lines is low.  This is because the average level of exposure in residences rarely exceeds 3 milligauss (0.3 microtesla).  As mentioned, according to the Israeli Ministry for Environmental Protection, the average level of exposure in most homes in Israel and abroad does not exceed 1 milligauss (0.1 microtesla).

 

According to various estimates, based on assessment of the rates of exposure to magnetic fields (subject to the model according to which the estimate was made), in different countries,  exposure to high-voltage power lines can account for no more than 1-4% of all cases of childhood leukemia.  Consequently, these evaluations state that even if a causal relationship between magnetic fields and childhood leukemia exists, the number of cases worldwide that can be attributed to magnetic fields ranges between 100-2400 per year, constituting 0.2-4.9% of the total incidence of the disease in one year (up to the year 2000).  Hence, even if magnetic fields indeed increase the risk of developing leukemia, the effect on public health is relatively limited.

 

Apart from the studies described above, public debate continues in Israel and abroad, relating to the restrictions required regarding exposure to magnetic fields, especially prolonged exposure to low frequencies of these fields, and relating to policy-making on the issue of exposure.

 

To read on Policy in Israel regarding exposure to the electric grid

      

Related articles:

Research methods for assessment of exposure to magnetic fields at the electric grid frequency in epidemiological studies

 

References

  • World Health Organization, Extremely low frequency fields environmental health criteria. Monograph No. 238. WHO (2007) Extremely low frequency fields environmental health criteria. Monograph No. 238,. Available at http://www.who.int/peh-emf/publications/elf_ehc/en/index.html
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