The Interphone Study found that brain cancer (glioma) occurred 3.5 times more often in people who talked on their cell phone for at least one hour every day over 4 years (accumulating 1640 or more hours of talk-time). Moreover, the tumours mainly occurred in the brain’s temporal lobe, nearest the ear to which the cell phone was held.
Although other studies reported a similar association, the Interphone Study Group appeared to doubt this disturbing finding, suggesting that any increase in brain tumours was of dubious significance. Why? Because the excess in gliomas was seen only at the highest level of cell phone use, with no evidence of any effect at low or moderate exposure to radiofrequency electromagnetic field (REF) emissions from cell phones. Indeed, there appeared to be a 20% decrease in brain tumours in all but the most avid cell phone users — something the authors dismissed as biologically “implausible”.
Their conclusions were based on a rigid adherence to the standard “linear dose-response” model of risk assessment favoured by toxicologists and health regulators: a chemical or physical agent (such as REF) must show a progressive linear (straight-line) rise in a harmful effect over a range of doses or exposures to be considered a danger to health. Yet, there are hundreds upon hundreds of examples of substances, or physical agents, including ionizing radiation, whose dose responses are not linear, but “J-shaped” or “hormetic” (derived from hormone, meaning differing effects at low and high levels of exposure). One notable example is alcohol: it is now widely accepted that low to moderate daily consumption of spirits increases longevity because of significant protection against cardiovascular disease, while higher consumption decreases longevity, in part by increasing cardiovascular deaths.
This and the all-too-many other exceptions to the linear rule led me to conclude that, “A ‘J-shaped’ dose-response (decreased risk of brain tumours with low to moderate use; increased risk with excessive use) is highly consistent with the findings of the Interphone Study Group.” Is it possible that the comments in my blog influenced scientists at the World Health Organization’s International Agency for Research on Cancer (IARC)?
While thinking so would be highly presumptuous, let alone erroneous, I certainly welcome the agency’s May 31st announcement that it has now put “radiofrequency electromagnetic fields…associated with wireless phone use”, on its Category 2B list of “possible [not proven] carcinogens. In reaching this decision, IARC scientists examined the findings of the Interphone study, among many others (both positive and negative), and decided it was “credible” that exposure to cell phone radiation could be a cause of brain cancer, although “chance, bias or confounding could not be ruled out with reasonable confidence.”
The IARC also correctly pointed out that some of the epidemiological studies it reviewed were carried out several years ago when cell phones emitted significantly higher levels of REF than those in use today. What undoubtedly did influence their thinking was a recent U.S. National Institutes of Health (NIH) study showing that holding a cell phone to the ear for 50 minutes markedly increases brain activity in the area closest to the antenna. Could a daily “revving up” of brain cell metabolism lead to the development of tumour years down the road? At this point, nobody knows.
Of even more potential concern, the study was carried out only in adults. What would be the long-term effect of cell phones on the brain tissue of children and pre-teens, whose thinner skull bones provide less protection from REF emissions? Responding to these concerns, Dr Nora Volkow, the lead NIH investigator, commented, “This study does not in any way indicate that [cell phones cause cancer]. What the study does is to show the human brain is sensitive to electromagnetic radiation from cell phone exposures.”
What does she, and the IARC recommend? More studies (of course). In the meantime, they also suggest that cell phone users buy an earpiece to keep the phone away from the head, or send text messages rather than speak (thank goodness today’s youngsters would much rather text than talk!). As for those teens who literally “wear” their turned-on cell phones next to their skin (for example, under the bra), or sleep with their head next to them on the pillow every night, officials caution that they should stop.
Final word: I continue to believe that, like exposure to alcohol and ionizing radiation, a J-shaped hormetic dose-response applies to REF emissions from cell phones. Unlike heavy users, adults who use their cell phones in moderation probably need not worry about an increased risk of brain cancer; the hormetic dose-response model predicts that they even may be protected!