A biophysicist weighs in on the NTP results.
The National Toxicology Program (NTP) study of the effects of cell phone energy on rodents has gotten widespread media coverage and has provoked discussion. My own article from several days ago attempted to examine important features of the study in order put the reported findings in perspective. As one can gather from examining the NTP technical report on the study and from the points I and others have made, a study like this raises many questions.
When confronted with the publication of a substantial study, like the NTP rodent study, there is an understandable desire to believe that it tells us something about what we want to know – in this case, whether radiofrequency (RF) energy from cell phones can promote cancer in humans. This applies to scientists as well as to non-scientists. But this is precisely what needs to be scrutinized and assessed critically. This is where the hard work of examining the methods and the results of the study in the light of what is known about RF emissions and cancer, in both rodents and humans, comes in.
In other words, we have a tendency to want the study to deliver a clear message, but there is no a priori reason why any experimental study – whether conducted in animals or in humans – must necessarily deliver a clear and relevant answer to the question that interests us.
The lead NTP scientist has stated that, “We believe that the link between radio frequency radiation and tumors in male rats is real, and the external experts agreed.”
In my column I pointed out characteristics of the study exposure which differ from the human situation involving cell phone use. In addition, I drew attention to the very small number of positive results, inconsistency of the results by sex, and questions about their relevance to cancer in humans. Raising questions is an essential part of the process of critically evaluating published evidence to see what it contributes to existing knowledge, in order to determine whether further and better studies can and should be done.
Since studies like this are extremely difficult to interpret and to assess in terms of their relevance to humans, I contacted Kenneth Foster, a professor of bioengineering at the University of Pennsylvania, who studies the interactions of non-ionizing electromagnetic energy, including radiofrequency energy, with biological systems.
I was curious to see what someone with his background had to say about the NTP study and whether he agreed with the points I raised.
Foster acknowledged that there does seem to be a trend in the heart schwannoma results in male rats, particularly for one of the frequency modulations (CDMA). The increase with GSM was never statistically significant.
But he went on to point out that, “None of these results are corrected for multiple comparisons, however, and I am sure that correcting for that would yield a totally negative study.” “Correcting for multiple comparisons” addresses the point I made in my column that one has to examine the highlighted result against the background (the denominator) of all analyses that were conducted. This is because if one conducts, say, 100 different analyses (looking at tumors in different organs in male and female rodents), just by chance alone, one would expect to obtain statistically significant results in 5 of those analyses.
Foster also addressed the biological mechanism involved in subjecting test animals to RF energy, “Another consideration is that the increase occurred at the highest exposure levels (6 W/kg whole body absorption). That is well above the level at which rats show behavioral thermoregulatory responses. The exposed rats maintained their core body temperatures (although some rats increased core temperature by a degree or so at 6 W/kg exposure), but that does not preclude significant metabolic changes due to the imposed heat load. The metabolic rate of adult rats is about 6 W/kg, i.e. comparable to the highest exposure levels used.”
He concluded, “So there are three possibilities: (a) a statistical fluke; (b) a real effect due to thermophysiological changes; (c) a direct effect of RF energy. Occam’s razor suggests that the first two are more likely.”
Foster’s closing comments were:
“The main effect of the study is that it will trigger another $20M or so in added research. Already 2 Asian countries are talking about repeating the study.”
And finally, “Seems to me to be a textbook example of fragile results. Try to explain that to the media however.”
Geoffrey Kabat is a cancer epidemiologist and the author, most recently, of Getting Risk Right: Understanding the Science of Elusive Health Risks.
Original Article can be found by clicking here