Biological effects begin at low levels
In 2011 AC magnetic fields were evaluated as possibly carcinogenic to humans (Group 2B) by the World Health Organization/International Agency for Research on Cancer (IARC).
This was based on the statistical association of higher-level residential ELF magnetic fields and an increased risk for childhood leukemia.
This follows the release of a number of recent meta-analyses (by Ahlbom, 2000; Greenland, 2000 and Doll, 2001) which found an increased risk of leukemia at 3-4 mG.
The lowest level linked to cancer for magnetic fields comes from the Swedish epidemiological study which reported increased leukemia for children at levels of 2.0 mG or more (Feychting & Ahlbom, 1993).
A German study has linked exposures of 1 mG to reduced survival rates of children trying to recover from leukemia (Svendsen, Weikopf, Kaatsch & Schuz, 2007).
A recent report by Li et al. (Li DK, Ferber JR, Odouli R, Quesenberry CP Jr. A Prospective Study of In-utero Exposure to Magnetic Fields and the Risk of Childhood Obesity. Sci Rep. 2:540, 2012) found an increased risk of obesity of humans exposed prenatally to magnetic fields at 2.5 mG (0.00025 mT).
Another study by Stevens (2007) indicating changes in emotional states in humans exposed to 8-12 Hz magnetic field at 50 mG (0.005 mT).
These studies do suggest magnetic fields at very low intensities can cause neurological effects in humans.
Studies show a clear link to harmful effects
In a study of more than 20,000 Swiss railway workers who were followed for 30 years, researchers found that certain workers risk of myeloid leukemia and Hodgkin’s lymphoma climbed in tandem with their exposure to very low-frequency magnetic fields.
Train drivers, who had the greatest exposure, were nearly five times more likely to develop myeloid leukemia than station managers, the workers with the lowest exposure to magnetic fields.
Drivers were also more than three times as likely to be diagnosed with Hodgkin’s disease, a cancer of the lymph system.
The findings appear in the journal Occupational and Environmental Medicine.
A recent study of real-world exposure to magnetic fields in pregnant women found a significantly higher rate of miscarriage, providing new evidence regarding their potential health risks. The Kaiser Permanente study was published December 13 2017 in the journal Scientific Reports (Nature Publishing Group).
Another study in 2011 was conducted on pregnant women that were exposed to elevated levels of magnetic fields during pregnancy. It found a much higher occurrence of asthma in offspring.
The findings of this study open up a new area in understanding the risk factors for asthma and the health effects of ubiquitous magnetic field exposure, especially during pregnancy.
Effects on Neurotransmitters
The next studies show the effects of magnetic fields at higher levels (above 0.01 mT / 100mG; the highest was 8 mT). The intensities are much higher than those commonly found in the public environment.
Neurotransmitters are chemicals that carry (transmit) signals from one nerve cell to another. Neurotransmitters are released from one nerve cell and react with molecules called receptors on another nerve cell.
The reaction alters the activity of the second nerve cell. Activities in nerve cell could also change the properties of these receptors (mainly by changing the concentration or the affinity of the receptors to neurotransmitters).
In the updated EMF literature, all the studies are on the effects of ELF EMF exposure on neurotransmitter receptors. Manikonda et al. (2007), Li et al. (2014) and Duan et al. (2014) reported effects of chronic ELF EMF exposure on NMDA receptors in the hippocampus of rodants.
Salunke et al. (2013) reported that ELF EMF-induced anxiety in the rat involved NMDA receptors in the brain. There is a report on effects of magnetic field serotonin and dopamine receptors in the brain of the rat (Janac et al., 2009).
Frilot et al. (2014) reported a change in NMDA receptor-mediated electrical activity in the rat brain after exposure a 60-Hz EMF. Changes in a subtypes of serotonin receptors 5HT(2A) in the prefrontal cortex was reported.
5HT (2A) receptors , particularly in the frontal cortex, are believed to be related to the psychiatric syndromes of depression in humans.
The serotonergic system is also implicated in the nocicetive effect of static magnetic field (Hernádi and László, 2014). Kitaoka et al. (2013) and Szemerszky et al. (2010) did report depression-like behavior in mice and rats, respectively, after chronic exposure to magnetic fields.
There are two reports on dopamine receptors. Shin et al. (2007, 2011) reported an increase in D-1 dopamine receptors and activity in the striatum of the rat after magnetic field exposure.
Dopamine in the striatum is involved in Parkinson’s disease. Wang et al. (2008) reported that ELF magnetic fields potentiated morphine-induced decrease in D-2 dopamine receptors.
Both D-1 and D-2 dopamine receptors in the brain are involved in depression and drug addiction.
Salunke et al. (2014) reported no significant change in serotonin and dopamine levels in the cortex, hippocampus, and hypothalamus of the mouse after chronic exposure to an ELF magnetic field.
However, these authors observed obsessive compulsive disorder-like behavior in the exposed mice, which could be relate to a change in nitric oxide in the brain.
There is one study on the cholinergic system. Ravera et al. (2010) reported changes in the enzyme acetylcholinesterase in cell membrane isolated from the cerebellum after magnetic field exposure.
Interesting, these researchers also reported ‘frequency window’ effects in their experiment. Window effects, i.e., effects are observed at a certain range(s) of EMF frequency or intensity, were first reported by Ross Adey and Susan Bawin and Carl Blackman in the 1980s.
A recently study by Fournier et al. (2012) reported an ‘intensity window’ effect of ELF magnetic field on neurodevelopment in the rat. The cholinergic systems in the brain play a major role in learning and memory functions.
There were a series of studies carried out more than a decade ago showing effects of ELF magnetic field on the cholinergic systems, e.g., Lai and Carino (1999) (60-Hz magnetic field and central cholinergic activity: effects of exposure intensity and duration.
Bioelectromagnetics 20:284-289, 1999). Not many studies have been carried out in recent years to further investigate the effects of EMF on this important neurological function.
Behavioral effects of ELF EMF have been further substantiated in recent research. These included:
- Changes in locomotor activity (Balassa et al., 2009; Dimitrijevic et al., 2014; Janac et al., 2012; Legros et al., 2012; Murugan and Persinger, 2014; Raus et al., 2012b; Sakhnini et al., 2012; Shin et al., 2007, 2011; Todorovic et al., 2012).
- Learning and memory functions (Che et al., 2007; Corbacio et al., 2011; Cui et al., 2012; Duan et al., 2013; Fournier et al., 2012; Fu et al., 2008; Harakawa et al., 2008; He et al., 2011; Liu et al., 2008b; Sun et al., 2010).
- Anxiety (Balassa et al., 2009; He et al., 2011; Korpinar et al., 2012; Liu et al., 2008a; Salunke et al., 2013)
- Autism-relevant social abnormalities (Alsaeed et al., 2014)
- Depression-like behavior (Kitaoka et al., 2013; Szemerszky et al., 2011).
- Perception (Ross et al., 2008).
- Cognitive dysfunction (Davanipour et al., 2014).
- Emotional state (Stevens, 2007).
- Sleep quality (Hung et al., 2007; Liu et al., 2014; Monazzam et al., 2014).
- Comb building in hornets (Ishay et al., 2007).
Since different behavioral effects have been observed in different exposure conditions, species of animals, and testing paradigms, they provide the strongest evidence that exposure to ELF EMF can affect the nervous system.
In some of these observed neurological effects, oxidative changes (free radicals) again seemed to play a role:
(Akdag et al., 2010, 2013; Akpinar et al., 2013; Cho et al., 2012; Chu et al., 2011; Ciejka et al., 2011; Deng et al., 2013; Coskun et al., 2009; Cui et al., 2012; Cui et al., 2012; Di Loreto et al., 2009; Duan et al., 2013; Falone et al., 2008; Kantar Gok et al., 2014; Liu et al., 2014; Manikonda et al., 2013; Martinez-Samano et al., 2012; Rauš Balind et al., 2014; Reale et al., 2014; Salunke et al., 2014; Selaković et al., 2013; Tassel et al., 2012a, Turkozer et al., 2008).
Increase in free radicals causes cellular damages. Most of these effects are changes in enzymes involved in maintenance of oxidative balance in cells.
A paper by Falone et al. (2008) reported an interesting finding. The researchers observed that, after magnetic field exposure, the brain of young rats showed an increase in anti-oxidative enzymes and defense against oxidative damage, whereas that of old rat showed a decrease.
Thus, aging may make an individual more susceptible to the detrimental effects of ELF EMF.
There are other factors that could affect an animal’s response to ELF EMF.
Janac et al. (2012) reported age-dependent effects of ELF EMF on locomotor activity in the Gerbils.
Reyes-Guerrero et al. (2010) found that the fields affected olfactory bulb estrogen receptors in female but not in male rats.
Sun et al. (2010) reported that, after in ovo (in the egg) exposure to ELF EMF, chicks showed memory deficit only when they were under stress.
Indeed, Lahijani et al. (2011) reported histological changes in the brain of chicks exposed to ELF EMF in ovo.