Dec 08 2009

Update on Cell Phones and Brain Cancer

A new study does not show any increase in brain tumors associated with increased cell phone use. This is just the latest bit of evidence of a large literature showing some mixed results, and it is far from definitive – but it is a bit reassuring.

The concern is that radiation from cell phone use, over years, increases the risk of brain tumors. I have summarized this research previously. Essentially, the evidence fails to find any increased risk of brain tumors for cell phone use of less than 10 years. For exposure of more than 10 years the evidence is less clear – an increased risk has not been definitively ruled in or ruled out, and more research is needed.

A recent review of the literature of cell phone use an acoustic neuroma (one type of brain tumor) found that the literature is simply inadequate to answer the question, and made recommendations for the type of studies that should be done. A 2008 meta-analysis of studies (since my last review) of cell phone use and brain tumors found:

We found no overall increased risk of brain tumors among cellular phone users. The potential elevated risk of brain tumors after long-term cellular phone use awaits confirmation by future studies.

So it seems the state of the research has not fundamentally changed in the last two years – for long term exposure (>10 years) we still need more study. But the fact that the data is equivocal probably means that there is no large effect. Smaller effects are harder to rule out.

Part of the problem with nailing down this question is the nature of the question itself. There are various kinds of evidence that can be brought to bare. The first is pre-clinical or biological – testing the basic science of cell phones and their biological effects, on cells or on animals. This research has failed to find a specific mechanism by which cell phones might cause brain tumors. However, it has found measurable biological effects. The most we can say at this point is that this kind of research provides some plausibility to a possible connection between cell phones and tumors, but it cannot answer whether or not cell phones have actually increased tumor risk.

The most definitive type of research would be experimental studies – studies in which things are done to subjects in a controlled manner. In experimental studies variables can be controlled for, or averaged out with randomization, and exposure can be maximally tracked. However, this type of study will never be done. It is both impractical and unethical – we cannot expose people deliberately to a potentially harmful substance to see what happens. Also – it is simply not practical to randomize people to either use or not use cell phones.

So we are left with observational studies – studies in which we simply observe what is happening or what has happened. This is the bulk of the relevant research on this question – looking at cohorts of people to see if cell phone use can be correlated with risk of developing brain tumors. This is the research I summarized above.

Observational studies are never definitive. We have to slowly build a picture of risk by looking at data from multiple angles.  We essentially triangulate risk by looking at multiple correlations.

This latest study by itself is rather weak evidence, but put into context, it adds to the growing body of observational studies and helps us build a more complete picture. This study looks at the overall incidence of brain tumors in a Swedish cohort (retrospectively). If cell phones cause brain tumors, then brain tumors should be on the rise following increased use of cell phones in the population. They looked at cohorts from the 1970s through 2003. Cell phone use sharply increased in the mid 1990s. What they found was:

During this time, the incidence rate of cancers known as gliomas increased gradually by 0.5% per year among men and by 0.2% per year among women.

For cancers known as meningioma, the incidence rate increased by 0.8% among men and, after the early 1990’s, by 3.8% among women.

This more rapid change for women was driven, the researchers say, by the 60-79 year age group.

So while there was a slow increase, likely due to other epidemiological factors, such as an aging population, they did not find any change in this rate of increase following widespread use of cell phones.

However, this study just supports the existing status of the research. It strongly supports of lack of a short term risk of cell phones, but does not really address the long term risk – > 10 years. If we take 1995 as the time when cell phone use significantly increased, then we need data from after 2005 to assess the risk of greater than 10 years of exposure, and this data only goes to 2003. So obviously we need a follow up study with data to 2008 or later. Hopefully we will have this data sometime soon.

Given the uncertainty in the literature, what should a prudent person do? There is no simple answer to this, as each person must weigh the risks of a small possible increased risk of brain tumors from long term cell phone use against the convenience of cell phones. We accept such risks all the time. Many of us accept the risks of driving for the convenience it brings, and this risk is likely much greater than that of cell phones. But you can manage that risk a bit by wearing a seat belt, driving a safe car, not driving while impaired, not using a cell phone or other distracting device while driving, and not speeding.

For cell phones there is no comparable list of easy things to do that clearly reduce possible risk. You can minimize unnecessary cell phone use. It may be useful to alternate which ear you hold the cell phone to, to spread out exposure. If you are going to have a long conversation from your home or office, use a land line. Hands free devices may be helpful, or you can hold the cell phone in front of you on speaker like a Star Trek communicator. Radiation blockers or other devices, however, are probably not helpful – there is no way to shield your head from cell phone radiation without shielding the signal the phones need to operate – so don’t fall for any magical device claims. It may also be prudent to limit or delay cell phone use in children.

It will probably be 5 years or more before we have a strong consensus on the long term risks of cell phone use. There is no way around the fact that long term risks require long term studies, and therefore take time. So be patient and stay tuned.

16 responses so far

16 thoughts on “Update on Cell Phones and Brain Cancer”

  1. scotth says:

    Would there be interest in a supplimentary article on this issue from a physics perspective? Perhaps “Why it is unlikely cell phones will ever be linked with cancer”.

    As a physics nerd and 8 years as a RADAR tech, I should be able to provide something useful.

  2. CrookedTimber says:


    An article
    in Skeptical Inquirer by S.T. Lakshmikumar discusses the physics of cell phone radiation (as well as power lines) and seems to conclude that the amount of radiation is vastly insufficient to cause cancer.

    “Unless one is willing to discard the concept of photons, Planck’s law, and the interaction between photons and atoms—and thus the entire body of quantum physics—it is simply not possible for the photons associated with either a power line or a cell phone to cause cancer.”

    Your thoughts?

  3. scotth says:

    Steve, those are exactly my thoughts.

    Unless we throw the photoelectric effect, and indeed all of quantum electrodynamics on the trash heap…. There is no way to conclude other than shining a flashlight on someone would be billions of times more dangerous than using a cell phone. Sitting by a fireplace should make someone virtually explode with cancer.

    The only thing I would add is that we have much better human data on the dangers of microwave (cell phone) RF than just the cell phone data. People who work in the RADAR and communications fields have spent decades receiving full body doses at far higher power than anything a cell phone could hope to deliver. If this effect is dose dependent, one would expect a cause/effect signal to show up in this population very clearly.

    From a plausibility perspective, cell phones causing cancer is right in there with homeopathy’s claim of water having memory.

  4. scotth says:

    And to be clear, it isn’t the “amount of radiation” that should be of concern, but the energy of each photon.

  5. CW says:

    I showed this blog and reference links to a co-worker, and his response was … “just because we think that there’s no link [between cell phone use and brain cancer] in the short term doesn’t mean that it won’t have a link in the long term. We should just account for the fact that it probably does happen because we can’t wait until it’s too late to do anything about it.”

    This seems to be a logical fallacy, but I’m not certain as to which one. It sounds like it’s Ad Ignoratum, but typically that involves just uncertainty, not believe in future evidence. False Dichotomy?

  6. johnc says:

    The inverse square law tells us that we’re kept reasonably safe as long as we don’t have extremely close proximity, which is exactly what we have when holding a cellphone to our ear, so I would keep an open mind.

    If cigarettes were as old as cellphones, we’d be looking at a clear ten years of safety, with some small amount of uncertainty past that point.

    Ultimately we are all guinea pigs on this one, anyone who claims to know how safe cellphones are has a nobel-winning expertise in physics, oncology and neurology combined.

    @scotth If you think microwave radiation is harmless, try putting your pet in a microwave oven. Wavelength is a rather important factor, as well as strength.

  7. johnc says:

    BTW – I’d be far more concerned about terahertz devices. There is some evidence they can mess with DNA, again,like microwaves, it’s about resonance, not energy:

  8. =/

    “It will probably be 5 years or more before we have a strong consensus on the long term risks of cell phone use.”

    Nature does not need a consensus from us. The physics is pretty clear, theoretically and empirically.

    The energy of a photon at the wavelengths used in telecommunications is far to low to produce the ionizing radiation required for DNA damage.
    And no, increasing the number of photons will not do anything different, just read about the photo-electric effect. And no, time of exposure will not do anything different for the same reasons.

    Thermal energy could be a different story, but a cell phone puts out a small amount of power. If you are concerned do a calorimeter study and see how much you can raise the temperature of a given substance via microwave heating. Over 4pi steradians the heat produced is trivial in the human body, and even if focused by the antenna in a cell phone the energy/area is very small.
    So cooking is out.

    Sorry Dr. Novella, but even allaying the fears of your readers by suggesting use of inverse square law (distance) or hands free is simply leading credence to the idea that there is a danger.

    Secondly, comparing a risk assessment with respect to automobiles, which have very sound physics behind how they can hurt you (F=ma and various conservation laws), and cell phones (which are all but ruled out by physics) can only serve to validate the fears of the general public.

  9. scotth says:

    Earlier I was confusing CrookedTimber’s post with a reply from Steve. Sorry if I confused anyone (besides myself).

    And johnc…. Read the link CrookedTimber posted, what I said, and Michael Varney is saying. This is open and shut. The inverse square law does not come into play (other than after the frequency has been increased to ionizing levels).

    And remember…. microwave ovens were originally known as ‘radar ranges’. That is because they are driven with parts straight from the world of RADAR. I know exactly how they work. It is true that high power RF can harm you, but only through thermal effects (making something hot). Giving cancer is something else entirely.

  10. Potato says:

    You’re forgetting that not everything is photoelectric. Physicists were screaming that biological effects of RF (not just cancer) were impossible, until after the effects were proven. Many animals (esp. birds) can navigate by the earth’s magnetic field. In birds at least, this depends on a free-radical recombination reaction that can be disrupted by an RF field. If cellphones similarly act on some free radical recombination reaction that through some biological pathway can lead to cancer (or attention/decision making changes that could lead to say car crashes) then it’s worth investigating, especially given the prevalence.

    Fortunately (unfortunately?) the effect, if there at all, appears to be very small, so it’s very difficult to tease out of these observational studies (which always have a number of confounds lying under the surface — one that was raised at the last conference was that one of the epidemiological studies was grouping people by cellphone use but not controlling for other RF exposure like WiFi or portable (non-cellular) phones in the home).

  11. TRC says:

    Although I know this comment will ratchet down the intellectual ‘atmosphere’ produced by comments thus far, I feel I must make it…

    Any cell phone/brain cancer discussion immediately I think HAS to include Ace Ventura:Pet Detective circa 1994.

    Jim Carey as Ace tells Lt. Einhorn to “Be careful with that phone…In time, you could develop a tumor”.

    Of course, I chuckle, and then think it’s ironic how Carey is now the poster boy for the anti-vaccination scare-mongering, and probably, would move off into the anti-cell phone usage campaign if there could be a connection found between autism and Verizon contracts.

    Keep up the great work, Dr. Novella! Love the blog!


  12. Tracy W says:

    What I find striking about the cellphone-cancer link story is that people are not abandoning cellphones en masse in response, any more than they are abandoning car driving. It seems that people are quite willing to tolerate risk as long as they personally directly see benefits from the behaviour.

    And car driving is worse in terms of a moral perspective because by driving a car you put other people, such as pedestrians, at risk. I still drive.

  13. DavidCT says:

    The vary term “cell phone usage” is a mixed bag. How many cell phones we use today are comparable in radiation output to the phones used in the past when the lack of towers required higher wattages. Heavy usage today with lower transmission wattage is not what it was 10 years ago. When we have more definitive studies in 5 years, will the equipment even be the same?

  14. tmac57 says:

    One thing is for sure, there is an increased risk of being mistaken for a schizophrenic when using a hands free device while walking alone in public.

  15. erichirota says:

    Didn’t a bunch of scientists from WHO come out with a letter accusing some of their execs being previously long term employees of Motorola? And isn’t the IARC funded by the Mobile Manufacturers’ Forums (an international association of telecom manufacturers) and the GSM Association (a manufacturer of mobile phones). The government is obviously putting pressure on the IARC and other research groups… Besides, my neighbor was recently diagnosed with a malignant glioma and he had a satellite dish for his internet that he was using for 10 years right next to his bed on his balcony, so idk…

Leave a Reply