Apr 30 2012

Another Cell Phone – Cancer Review

There is an ongoing scientific discussion about the safety of long term cell phone use. The primary question  is whether or not long term exposure to non-ionizing radiation can increase the risk of brain cancer. There are further questions about whether or not such radiation can cause any health problems or symptoms.

As with any complex area of scientific research, perhaps the best way to evaluate the question is to put together a panel of experts to review all the existing evidence and then come up with a consensus opinion about that evidence. This is no guarantee of being right – the primary issue that tends to come up with such expert panels is that they were systematically biased toward one side of the debate. But assuming no major asymmetry in the constitution of an expert panel, they are an excellent way to evaluate the current state of the evidence on a specific question. Even better, of course, is when multiple independent panels all agree.

Recently an expert panel for the UK’s Health Protection Agency (HPA) reviewed the evidence for cell phone safety concluded that there is no clear evidence for any harm. This is good news. Their findings are similar to other reviews of the evidence, although often there is a difference in emphasis. For example, last year the International Agency for Research on Cancer (IARC) reviewed the same evidence and concluded that:

 “the evidence, while still accumulating, is strong enough to support a conclusion and the 2B classification. The conclusion means that there could be some risk, and therefore we need to keep a close watch for a link between cell phones and cancer risk.”

They are not really saying anything different from the HPA – both groups concluded that there is no clear evidence of risk, but that further monitoring is prudent. The HPA, however, chose to emphasize that there is no conclusive evidence of risk, while the IARC chose to emphasize that there is no conclusive evidence that there is no risk. There  classification means that there may or may not be a risk, but further research is warranted. Meanwhile the FDA has concluded that: “the weight of scientific evidence has not linked cell phones with any health problems.” The Federal Communications Commission has this to say:

“There is no scientific evidence that proves that wireless phone usage can lead to cancer or a variety of other problems, including headaches, dizziness or memory loss. However, organizations in the United States and overseas are sponsoring research and investigating claims of possible health effects related to the use of wireless telephones.”

These all sound like variations of the same conclusion – there is no clear evidence of harm or risk, but we should continue to do research and monitor the results. Overall there is more caution when children are concerned, because there are fewer studies, children’s heads are smaller, and if cell phone use is started at a young age then lifetime use will be greater. Still there is no evidence of harm, but there are a priori reasons for greater caution.

Getting back to the new review by the HPA, here are their key conclusions:

  • The evidence suggests that RF field exposure below guideline levels does not cause symptoms in humans and that the presence of RF fields cannot be detected by people, including those who report being sensitive to RF fields.
  • A large number of studies have now been published on cancer risks in relation to mobile phone use. Overall, the results of studies have not demonstrated that the use of mobile phones causes brain tumours or any other type of cancer.
  • As mobile phone technology has only been in widespread public use relatively recently, there is little information on risks beyond 15 years from first exposure. It is therefore important to continue to monitor the evidence, including that from national brain tumour trends. These have so far given no indication of any risk.
  • Studies of other RF field exposures, such as those at work and from RF transmitters, have been more limited but have not given evidence that cancer is caused by these exposures.
  • Research on other potential long-term effects of RF field exposures has been very limited, but the results provide no substantial evidence of adverse health effects; in particular for cardiovascular morbidity and reproductive function.

There are several types of evidence that address this question. The first is the basic science plausibility of health effects from non-ionizing radiation. By definition, non-ionizing radiation (like radio-frequency radiation used by cell phones) is not energetic enough to break chemical bonds. It therefore should not cause DNA mutations, which is believed to be the primary mechanism by which high energy radiation causes mutations that lead to cancer. Some scientists have concluded from this that cell phones cannot possibly cause health effects, and while this conclusion may be true it is a bit premature. More subtle biological effects are not likely but are also not completely implausible. There is some local tissue warming, for example. The magnitude of this effect is very small, but it is not zero. My own feelings on the question is that biological effects from cell phone radiation is very unlikely, but it would be premature to declare them impossible. Therefore clinical research into the effects of chronic cell phone use are warranted.

There are two basic types of clinical evidence – observational and experimental. We do not have any experimental data on cell phones and humans because such studies are both unethical and impractical. You cannot randomize study subjects to either be exposed to or not be exposed to a potential environmental risk factor. You can’t force people to use cell phones (or smoke, or eat a possible toxin, etc.) to see if they cause harm. So we have to get by with observational data.

There have been a number of observational studies of cell phones and brain cancer. They generally take two forms: either looking at people with and without brain cancer and then finding out their cell phone use history, or dividing people into groups based on their cell phone use and then following them for their subsequent rate of brain cancer. We can also look at overall brain cancer incidence to see if it correlates with overall cell phone use.

These are the studies that the above expert panels and agencies have been reviewing, and which do not show a clear correlation between cell phone use and brain cancer. One limitation of such studies is that they cannot be extrapolated beyond the duration of observation. We now have about 15 years of observational data for cell phone use, so our conclusions about safety from this data are limited to about 15 years. We cannot know that cell phone use is safe when used for 20 or 30 years until after we have observed effects for that long.

Another way to look at this type of data is this – if we take the hypothetical situation that there is zero health risk from cell phone use, what would our observational data look like? We would never be able to prove that the risk is zero. Rather, the more data we gather then the smaller the possible remaining risk (risk that is too small to be detected by the current data). This uncertainty will approach, but never quite reach, zero. So we can never prove a zero risk, but we can increase our confidence that the risk is too small to worry about. Also, the longer we gather data and make observations then the longer the period of exposure over which we can say there is likely no risk.

Of course if there is a small risk from cell phones the data will look exactly the same, until we gather enough data to detect with statistical confidence this small risk.

Agencies and panels who have reviewed the data all agree that we have not detected a statistically significant risk from cell phone use out to the current limits of the data – 15 years. They also all agree that we should continue to conduct research and monitor cancer rates. Where there is some difference is in the application of the precautionary principle. Given this current state of the data, how cautious should we be about the potential health risks of cell phones. There is no objective scientific answer to this question. This comes down to philosophy and personal choice. How valuable, for example, are cell phones? Many people find their convenience worth even a known small risk, let alone a possible but unproven small risk. We also have to consider how many lives are saved by the availability of cell phones in emergency situations.

Cars are an obvious analogy to cell phones. In the US there are about 40,000 motor vehicle related deaths per year. This is far more than the possible remaining risk from cell phone use, given current evidence. Yet, we accept this risk because of the convenience that motor vehicles provide, in addition to being a critical part of the infrastructure of our modern society.

It is interesting to think about what risk you would accept from cell phone use. Let’s say that eventually we find there is a small increased risk of cancer from cell phones. At what point would you conclude that this risk is high enough to stop using cell phones? I think there is sufficient evidence to conclude that we are already below that number for me personally. Even if there is a small risk, it is too small to worry about. But I also welcome reassurance from further research.

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