Too many studies and discussions on potential health risks fail to address critical variables, such as distance and transmit power variability between handsets and air interface technologies.
A statement from the World Health Organization (WHO) that cell phone use may increase the risk of brain cancer is making a lot of industry executives nervous. Lingering concerns of this nature have left a cloud hanging over the industry for decades despite numerous studies that appeared to indicate, at worst, a statistically insignificant link.
The cell phone/cancer controversy was supposed to have been put to rest last year with publication of the findings of the Interphone study, a landmark international effort involving a number of highly respected research institutions. That study’s official general conclusions were that cell phone use does not result in a statistically significant change in the risk of contracting either of two forms of brain cancer. Now, however, the WHO is citing that same Interphone study as potential evidence of elevated risk.
The published findings of the Interphone study were welcomed by the wireless industry, but they hardly brought an end to public concerns regarding cell phone safety. The city of San Francisco, for example, is considering an ordinance requiring that cell phones come with a radiation hazard label. Recently, the controversy has been given greater public exposure through several television pieces presented by Dr. Sanjay Gupta, a neurosurgeon who is also a popular on-air contributor on CNN. In one presentation, Dr. Gupta takes issue with the Interphone study, claiming that an indication of somewhat increased brain cancer risk among long-term cell phone users was mostly ignored in the study’s published results and conclusions. More on that later.
The issue of long-term cell phone use was also raised in Dr. Gupta’s interview of Dr. Keith Black, an internationally renowned scientist who is chairman of neurosurgery at Cedars-Sinai Medical Center in Los Angeles. Dr. Black pointed out that brain cancers may take many years to develop, while cell phone use has only been virtually ubiquitous in the U.S. and other developed countries for a relatively short time. And, according to Dr. Gupta, many other prominent neurosurgeons have expressed similar “latency” concerns.
The problem I have with studies like Interphone, and with discussions and presentations on the topic of potential health risks, is they often fail to address critical variables associated with cell phone use. To users, the most obvious of these is differentiation between holding the phone to one’s ear for voice calls and having the phone farther from the head, as would be the case when using a Bluetooth or wired headset and for most data applications.
To their credit, both the Interphone study and Dr. Gupta’s presentations do make this distinction, while others do not. But even when the focus is exclusively on the “worst-case” phone-to-the-ear use, most analyses completely ignore the enormous variability of handset transmit power that exists in various environments and between different network technologies. Since the physiological effect that is of concern is heating of brain tissue (much like food is heated in a microwave oven), and since such heating will be linearly proportional to the absorbed RF energy, the potential risks associated with cell-phone-to-the-ear calling, if any, will obviously be greatly dependent upon handset transmit power level.
Consider, for example, a cell phone engaged in a voice call on a CDMA (1XRTT or UMTS) channel. The cell phone may have a maximum transmit output power capability of around 200 mW (+23 dBm), but in a typical outdoor urban environment, it is likely to be transmitting at under one mW (0 dBm), and often much less. This transmit power variability is probably at least as significant, in terms of the amount of energy absorbed by any particular area of the brain, as whether the phone is held to the ear or a foot or so away.
GSM, CDMA AND OTHERS
An even bigger factor usually ignored by studies and discussions dealing with cell phone safety is the differences between air interface technologies. In a GSM system, handset transmit power will typically be dynamically adjusted so as to provide a signal strength at the base station receiver input of around -90 dBm. For CDMA systems, the level (while speech is present) is typically more like -115 dBm, around 25 dB lower. A GSM phone transmits only one-eighth of the time during a call, and with typical speech activity, a CDMA phone usually transmits at an average power about 3 dB below what it does when speech is present. Factoring in these corrections, it is reasonable to assume that, on average, GSM phones will transmit at a power level roughly 20 dB (a factor of 100!) higher than CDMA phones for voice calls.
Obviously, the variability in handset transmit power associated with operating environment and network technology might have an enormous impact on any potential health risks associated with cell phone usage. This suggests that both the wireless industry and the public at large might be well served by scientific studies that correlate physiological effects with handset transmit power as well as position of the handset relative to the user’s head.
On the other hand, it is tempting to take the official conclusions of the Interphone study at face value and assume that, irrespective of such factors, cell phone use doesn’t appear to cause brain cancer. After all, while the phenomenon of just about everybody having a cell phone is pretty recent, substantial portions of the population in many western countries have been using them for decades. One would suspect that if there were a definitive link, we would by now be seeing a significant increase in brain cancer rates – something that does not seem to have occurred.
With the new WHO warning, I doubt that such an “absence of effect equals absence of cause” argument will be effective, and perhaps it shouldn’t. The factor in the Interphone study that troubles the WHO is that, as Dr. Gupta recently noted, “The data showed people who used a cell phone 10 years or more doubled the risk of developing a glioma, a type of brain tumor.” Dr. Gupta went on to say: “Across the board – most of the studies that have shown an increased risk are from Scandinavia, a place where cell phones have been popular since the early 1990s. For these reasons, the whole issue of latency could become increasingly important.”
What else is interesting about Scandinavia is that since the early 1990s and until very recently, voice cell phone calls have used GSM channels almost exclusively. Also, while I don’t have specific data to prove this, I would suspect that owing to the relatively low population densities in Scandinavia, average handset transmit power is likely higher there than in some other regions.
In fact, I would suggest that the factor of average handset transmit power is at least as important as “latency” when it comes to potential health risks. This is something we in the industry should be concerned about because it is likely that “voice over LTE” (VoLTE) service, to be inaugurated next year by Verizon, will entail higher average handset transmit power than even GSM, and much higher than the CDMA service it is expected to ultimately supplant.
The WHO and Drs. Gupta and Black think more studies are needed. Perhaps they are needed. But next time, they should focus on handset transmit power level as a primary variable of concern.
Drucker is president of Drucker Associates. He may be contacted at firstname.lastname@example.org.