Nam KC, Lee JH, Noh HW, Cha EJ, Kim NH, Kim DW. Hypersensitivity to RF fields emitted from CDMA cellular phones: A provocation study. Bioelectromagnetics. Jun 23, 2009 Ahead of print.
According to studies conducted in Sweden and the US, 1.5% and 3.2% of the population experience self-attributed electromagnetic hypersensitivity (EHS). Symptoms include headache, insomnia, nervousness, distress, fatigue, and short-term memory loss, most frequently attributed to exposure to mobile phone base stations (74%), mobile phones (36%), cordless phones (29%), and power lines (27%). However, previous studies do not indicate that people can perceive radio frequency electromagnetic fields (RF-EMF) or that their symptoms are directly invoked by them, suggesting that EHS is psychosomatic. Nonetheless, few studies have been conducted with Code Division Multiple Access (CDMA) technology, widely used in North America; similarly, few studies have investigated physiological parameters, subjective symptoms, and EMF perception simultaneously for both EHS and non-EHS groups.
To test whether EMF emitted from CDMA cellular phones influences heart rate, heart rate variability (HRV), respiratory rate, or gives rise to subjective symptoms in EHS and non-EHS subjects.
A total of 37 subjects participated in the experiment: 18 healthy EHS subjects recruited by advertisements in a University Hospital System and 19 healthy non-EHS subjects who were graduate school students and hospital staff. Subjects were in a supine position for the duration of the experiment (64 minutes) and a CDMA mobile phone was mounted on the left side of the head. Subjects were randomly assigned to receive either real or sham exposure on one day, followed by the other exposure on the next day. Subjects were blind to the exposure condition. The subjects’ heart rates, respiration rates, facial temperature, and HRV were obtained pre-test, after 15 min of exposure, after 31 min of exposure, and 10 min after exposure termination. Subjects were verbally asked about symptoms (headache, itching, warmth, etc.) several times during the exposure. Every 5 minutes throughout the session, subjects were asked if they felt any EMF.
There was no statistical difference in age, male-female ratio, body mass index, and cellular phone use between EHS and non-EHS subjects. There was no difference in facial temperature, heart rate, or respiration rate, between real and sham exposures for either the EHS and non-EHS subjects. There was a significant change in HRV from pre-test levels in both EHS and non-EHS groups. However, this trend was observed in both real and sham exposures. Neither the EHS nor non-EHS groups showed statistically significant differences between real and sham exposures for all nine subjective symptoms surveyed. Under sham conditions, the perception accuracy of the non-EHS group was higher than that of the EHS group. Under real conditions, perception accuracy of EHS subjects increased as the session progressed, while that of non-EHS subjects did not.
Interpretation and Limitations
The increase in HRV as the session progressed was likely due to increased drowsiness among the subjects caused by being in a supine position in a quiet room for an extended period of time. The difference in perception could be due to the belief among EHS subjects that they could detect EMF, causing them to answer in the affirmative more often. Similarly, non-EHS subjects assumed they could not detect EMF and were more likely to answer in the negative. This study was limited by the small sample size.
Exposures from CDMA phones did not have any effects on heart or respiration rate or subjective symptoms in either group. There was no evidence that the EHS group better perceived EMF than the non-EHS group.