Soderqvist F, Carlberg M, Mild KH, Hardell L. Exposure to a 890MHz mobile phone-like signal and serum levels of S100B and transthyretin in volunteers. Toxicological Letters. May 7, 2009 Ahead of print.
The blood-brain barrier (BBB) controls the transport of molecules between the blood and brain tissue. Its integrity protects the central nervous system from substances in the blood that are toxic to the brain. The same applies to the blood-cerebrospinal fluid barrier (BCSFB).  Low-intensity microwave radiation has been hypothesized to damage these barriers, although no experimental studies have been done in humans.  Changes in the blood concentration of brain-derived proteins, such as S100B and transthyretin (TTR) can be used to evaluate the integrity of these barriers.

The aim of the study was to investigate the association between exposure to a mobile phone-like signal and markers of blood-brain barrier and blood-cerebrospinal fluid barrier integrity, namely blood concentrations of S100B and transthyretin.

In total, 44 volunteers aged 18-30 years were recruited from the municipality of Umeå in Sweden.  Three participants were excluded from the study for health reasons. Participants were asked not to wear a wireless phone the day before or on the day of the experiment.  The experiment took place during normal working hours, from 8am to 5pm.  Blood was drawn 30 minutes before exposure, just before exposure, immediately after 30 minutes of microwave exposure, and 60 minutes after exposure. During exposure, subjects were seated in a reclining chair in front of a LCD computer screen watching a DVD.  An antenna emitting radiation was mounted on the side of the head the subject usually held their phone to.

For both S100B and transthyretin, mean and median serum concentrations decreased from the first to the fourth blood draw. No other statistically significant changes in blood concentration were observed for S100B. For transthyretin, no immediate change in blood concentrations was observed following exposure, although a statistically significant increase from the third to fourth blood draw was observed.  Overall, similar results were seen for men and women.

Interpretation and limitations
The results showed no statistically significant increase in the serum concentration of S100B after exposure to microwave radiation.  Hence, using S100B as a marker of blood-cerebrospinal fluid barrier integrity, no effect of microwaves could be seen. Serum transthyretin concentrations increased following exposure to microwave radiation. The decreasing trend in serum concentrations, especially for S100B but also in the first and second samples for transthyretin, indicated either a problem with the pre-analytic stability of the blood sample, or the influence of some external factor other than the microwave exposure, such as stress, which is plausible.  A larger study in which participants are randomized to receive real or sham exposure is needed to confirm that there really is an effect of the microwave exposure on serum transthyretin.

The clinical significance of the study findings, if any, is unknown.  Further randomized studies with use of additional brain specific markers are needed.

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