鈥�This article was first published in听.
If anyone ever tried to convince you that cellphones cause brain cancer, they probably referred to the U.S. National Toxicology Program (NTP). In 2016, the NTP published preliminary results suggesting that cellphones increased the risk of brain and heart cancer. The wave of concerned headlines was predictable. Many criticisms could be made about the study, but the main one was that the final data had not been published.
Fortunately, we now have the听final report听and can look at the data more carefully.
A few things to mention before we begin: The positive finding occurred in rats, but not mice. The positive finding听occurred in male rats, but not female rats. There were no humans in this experiment. The authors used the word 鈥渆quivocal鈥� a lot.
Now, let鈥檚 examine the data. The scientists exposed their animals (starting when they were embryos) to cell phones for nine hours a day, every day for two years. They then examined them for several kinds of cancer.
Ultimately, the only positive finding was an increased incidence of cardiac schwannomas, a rare form of cancer you probably have never heard of.
Contrary to what is being reported, the study did not show an increased risk of brain cancer (see Table 22 on Page 102 of the report if you don鈥檛 believe me). There were too few cases to demonstrate a statistical trend, and in fact the rates of brain cancer went down as cellphone power output was increased, which is nonsensical.
Finally, the report actually showed that those rats exposed to cellphones lived longer than the control group. Thus a more appropriate headline could have been, 鈥淐ellphones make you live longer鈥� rather than 鈥淐ellphones cause cancer.鈥�
The problem with the cellphone-cancer discussion is that it lacks biological plausibility. Cellphones emit radio frequency waves, which is actually quite different from what most people understand as 鈥渞adiation.鈥� Energy exists on a spectrum, of which we are only able to perceive a very narrow band, visible light.听We can see red, orange, yellow, green, blue, indigo and violet light, but nothing else.
Beyond violet light we have we have ultraviolet or UV radiation, which is emitted principally by the sun. Beyond that, we have X-rays and gamma rays. All these forms of radiation are called ionizing because they are high-energy waves and have the ability to damage DNA when passing through human tissue. Ionizing radiation is well known to cause cancer.
But at the other end of the spectrum, beyond red light, are infrared light, microwaves, radio waves and TV signals. These are non-ionizing radiation. They are low-energy signals and do not have the ability to alter or damage DNA. Non-ionizing radiation, like radio frequency waves, can heat up body tissues exposed long enough (that is how your microwave works), but cannot disrupt DNA. So if someone wants to posit that cellphones cause cancer, they must first explain how, exactly.听
So why did this study show a positive result if cellphones don鈥檛 cause cancer? Remember the association was only in rats, not mice, and only in male rats, not females. Also they tested nine different forms of cancer in four groups of animals, which led to 36 comparisons. If you accept a 5 per cent false positive rate (standard in medical statistics), the probability that you would have at least one false positive here is about 84 per cent. Given that we have a single positive finding among many negative analyses, I think we can assume it was a false positive.
If the statistics are not enough to reassure you, remember that this study probably doesn鈥檛 apply to you anyway. You probably don鈥檛 talk on your cellphone for nine hours a day. Also you are probably a human, and not a rat.
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