Researchers atWashington University School of Medicine
have found that the electromagnetic radiation produced by cell phones does not activate the stress response in mouse, hamster or human cells growing in cultures.
The stress response is a cellular protection mechanism set into motion by various adverse stimuli, including heat shock, heavy metals, and inflammation. High levels of the stress response in cells are thought to result in changes associated with malignancy.
"We performed highly sensitive, extremely well-controlled tests on living cells irradiated with energy like that from mobile phones, but at levels 5 to 10 times higher than those set for the devices by regulatory agencies," said Andrei Laszlo, PhD, associate professor of radiation oncology and a researcher at the Siteman Cancer Center at Barnes-Jewish Hospital and Washington University School of Medicine.
Prior research into the effect of cell phones on the stress response has been fraught with contradictory results, which in part may be due to less-than-ideal experimental conditions. For example, in the past it has been difficult to prevent temperature changes caused by microwave exposure.
Because heating of tissues has been shown unlikely to be a component of the effect of cell phone radiation on biological systems, Laszlo and his group sought to reduce as far as possible any heating of the cells in culture during the study. Using sensitive equipment that continuously monitored and adjusted temperature, they were able to keep temperature variations to plus or minus 0.3 degrees centigrade.
The researchers tuned their room-sized irradiator to emit cell phone frequency microwaves for both FDMA (frequency domain multiple access—used for cell phone analog signals) and CDMA (code domain multiple access—used for digital signals) modulation at power outputs standard for mobile phones. The large size of the irradiator enabled them to expose a large number of living cells so that sufficient material could be collected for highly accurate measurements.
To test whether the cell's stress response was activated by irradiation, the group looked for activation of a protein called heat shock factor (HSF). The activation of HSF is a necessary first step in the cascade of events that induce the stress response.
Under both short-term exposures (5-60 minutes) and long-term exposures (1-7 days), all tests on the cells in culture showed that HSF was not activated by microwave radiation of either type, indicating the stress response was not initiated.