Investigators found changes in brain glucose metabolism as measured by PET in subjects using cell phones, but no clear associative links with disease were detected.
DR. NORA D. VOLKOW led the research team that compared PET scans of 47 study participants under two circumstances: when they had 50 minutes of cell phone exposure and when they had no immediate exposure.
Cell phone use increases metabolic activity in regions of the brain near the antenna, but whether the finding has health implications is not known, according to a new study.
Researchers performed brain scans on 47 study participants under two circumstances: when they had 50 minutes of cell phone exposure and when they had no immediate exposure.
“Compared with no exposure, 50-minute cell phone exposure was associated with increased brain glucose metabolism in the region closest to the antenna,” the researchers reported in the Feb. 23 edition of the Journal of the American Medical Association. They noted, however, that “this finding is of unknown clinical significance.”
The study received widespread coverage in the media and helped stir the ongoing debate over whether exposure to the low-level radiation (radiofrequency-modulated electromagnetic fields, or RF-EMFs) emitted by cell phones might be causing health problems that will only become apparent as time goes on.
A key question has been whether cell phone use, particularly when it is heavy, increases the risk of developing brain cancer. Some epidemiological studies have pointed to an increased risk for brain tumors, but other research has been inconclusive or found no connection between cell phone use and cancer. Studies using brains scans to study changes in cerebral blood flow associated with cell phone use also have yielded mixed results.
In the latest study, conducted by researchers at the NIH and Brookhaven National Laboratory, the nearly four dozen study participants each underwent two PET scans with an injection of fluorodeoxyglucose to provide a look at brain glucose metabolism, which is a measure of cell activity.
In one case, the participants were outfitted with a cell phone on each ear, though both phones were turned off. In the second case, the right phone was turned on to receive a call from a recorded message, though the sound was turned off so that auditory stimulation did not confuse the results. Both cell phone “sessions” lasted 50 minutes and the participants were blinded to the experimental conditions.
“Whole-brain metabolism did not differ between on and off conditions,” wrote the research team, headed by Nora D. Volkow, MD, an investigator and director of the NIH National Institute on Drug Abuse. “In contrast, metabolism in the region closest to the antenna (orbitofrontal cortex and temporal pole) was significantly higher for on than off conditions.” There was about a 7 percent increase in metabolic activity when the cell phone was turned on, according to the report. The regions with stepped-up activity correlated with those areas that were thought to have the greateast absorption of RF-EMFs.
“These results provide evidence that the human brain is sensitive to the effects of RF-EMFs from acute cell phone exposures,” the researchers wrote. “The findings of increased metabolism in regions closest to the antenna during acute cell phone exposure suggest that brain absorption of RF-EMFs may enhance the excitability of brain tissue.”
But the researchers were clear to say they didn't know why that was the case, though they did put forth some hypotheses.
“The mechanisms by which RF-EMFs from cell phones could affect brain glucose metabolism are unclear,” they wrote. “However, based on findings from in vivo animal and in vitro experiments, it has been hypothesized that this could reflect effects of RF-EMF exposure on neuronal activity mediated by changes in cell membrane permeability, calcium efflux, cell excitability, and/or neurotransmitter release.”
They noted that “disruption of the blood-brain barrier has also been invoked as a potential mechanism by which RF-EMFs from cell phone exposure could affect brain activity.”
It has also been suggested that the heat generated when a cell phone is placed against the head might have a detrimental effect, the reearchers said. In the case of this experiment, however, the changes in brain activity occurred closest to the antenna, not where the cell phone came in contact with the head.
“These results provide no information as to their relevance regarding potential carcinogenic effects (or lack of such effects) from chronic cell phone use,” the researchers wrote. “Further studies are needed to assess if these effects could have potential long-term harmful consequences.”
In an editorial accompany the study, Henry Lai, PhD, professor of bioengineering at the University of Washington in Seattle, said the study results “add to the concern about the possible acute and long-term health effects of radiofrequency emissions from wireless phones, including both mobile and cordless desktop phones.”
“Although the biological significance, if any, of increased glucose metabolism from acute cell phone exposure is unknown, the results warrant further investigation,” he noted.
In an interview with Neurology Today, Dr. Lai pointed out some limitations of the cell phone experiment: It involved just one model of phone and offered a snapshot of brain activity during just a short period of time. Cell phones come in a variety of designs and emit varying levels of low-level radiation. Dr. Lai has found DNA damage in brain cells of rats exposed to radiofrequency radiation.
“The main question asked by this study was whether using a cell phone can bring about changes in brain activity. The study shows that, yes, there are changes,” Dr. Lai said. But the study was not designed to answer “whether you see these changes after long-term use. Does cell phone use cause some kind of long-term damage?”
“Could the findings of Volkow, et all be a marker of other alterations in brain function from radiofrequency emissions, such as neurotransmitter and neurochemical activities?” he wrote in the editorial. “If so, this might have effects on other organs leading to unwanted physiological responses. Further studies on biomarkers of functional brain changes from exposure to radiofrequency radiation are definitely warranted.”
But the study may not do much to sway those who feel there is little scientific evidence to worry about cell phone safety.
Gary W. Arendash, PhD, research professor at the Florida Alzheimer's Disease Research Center at the University of South Florida, told Neurology Today that he is troubled by the implication that the changes in brain metabolism observed in the study must mean something bad.
“They are assuming that if there are going to be any long-term effects they are going to be harmful ones,” he said. “An increase in neuronal activity may be beneficial to human health; in particular it may be protective against Alzheimer disease.”
Dr. Arendash has published research involving mice that shows that exposure to the electromagnetic waves generated by cell phones may protect against the memory impairment caused by Alzheimer's disease and may in fact reverse the accumulation of amyloid beta. Dr. Arendash is hoping to replicate his mouse studies in humans.