Blood-brain barrier

In the brain, there is a network of fine capillaries, which provides e.g. nutrients and oxygen to the nerve cells. The walls of these vessels exhibit special features in comparison to other capillary vessels in the body. The endothelial cells which line the vessels in the brain have no pores (fenestrations) for the transport of substances. Moreover, they are connected to each other by so called tight junctions at their edges. Both features prevent an uncontrolled passage of most substances (glucose, most amino acids, but also drugs and germs) into the brain. Only few small molecules can pass the semipermeable cell membrane of the endothelial cells without hindrance per diffusion (lipophilic substances and gases) or are able to slip through the spaces between plasma membranes of adjacent cells despite tight junctions (e.g. urea and glycine). Thus, all other substances which are to be transported from the blood into the brain or vice versa, have to be channeled through the vessel wall cells (endothelial cells) by special transport systems. This makes a controlled exchange of substances between the nerve cells and the blood possible and protects the nerve cells against harmful substances. This barrier is called the blood-brain barrier.

Theoretically, an increase of the permeability of the blood-brain barrier could lead to a transfer of undesirable substances and as a consequence to possible brain damage. The permeability of the blood-brain barrier is subject to temporal fluctuations even under normal physiological conditions, though it can be additionally affected by external factors. According to a statement by the German Federal Office for Radiation Protection (BfS, online 2016), it is e.g. indisputable that an increase of temperature in the brain causes an increase of the blood-brain barrier’s permeability. This can happen due to fever but also in the case of temperature rises caused by radiofrequency electromagnetic fields at intensities distinctly above the legal limits (following ICNIRP, at 7 W/kg or more (ICNIRP 2009, p.190). The object of research was to find out if the blood-brain barrier can also be damaged by radiofrequency electromagnetic fields below these limit values.

The effect of mobile phone related electromagnetic fields on the permeability of the blood-brain barrier have been investigated in several studies. A survey of all experimental studies on this subject can be found in the study overview on mobile phones in the EMF-Portal.

Different international and national committees evaluate existing data consistently regarding the evidence of an effect of radiofrequency fields on the blood-brain barrier. According to the International Commission on Non-Ionizing Radiation Protection (ICNIRP), most studies did not find any effect of radiofrequency electromagnetic fields below the limit values on the blood-brain barrier. The few studies with positive results were mostly older studies with methodical deficits, such as small groups or insufficient description of exposure and dosimetry. Thus, they had a limited validity (ICNIRP 2009, p.190 ff). The Scientific Committee on Emerging and Newly Identified Health Risks of the EU agrees with this opinion (SCENIHR 2015, p.128).
In a synopsis of all present studies and with reference to the results of the German Mobile Telecommunication Research Programme (DMF), the German Commission on Radiological Protection (SSK, 2011, p.23) does not see sufficient evidence for an effect of radiofrequency electromagnetic fields below the legal limits on the blood-brain barrier. Hence, it does not see any need for further research into this topic.
The Swiss Federal Office for the Environment (FOEN, 2014, p.27) also deems the evidence with regard to an effect on the blood-brain barrier from present literature insufficient. According to the FOEN, evidence for an effect originates mainly from studies by a single Swedish research group (Salford et al. 1994, Salford et al. 2003, Eberhardt et al. 2008, Nittby et al. 2009, Nittby et al. 2011 among others). Following the FOEN, all of these studies exhibit methodical deficits regarding the collection and analysis of data and the description of dosimetry, and there is no information available whether the temperature was controlled during exposure. Moreover, the observed effect has no relevance on health. Aside from these studies, evidence for an effect of radiofrequency electromagnetic fields on the blood-brain barrier is deemed very weak.

To summarize, it can be concluded, that international and national expert committees assume that there are no effects of radiofrequency electromagnetic fields on the permeability of the blood brain barrier. A new and detailed opinion from WHO regarding effects of radiofrequency electromagnetic fields is expected in 2016 (WHO Fact sheet № 193, 2014).