Our civilization is increasingly bathed in electromagnetic fields, including radio frequency waves, microwaves, and higher frequencies. It is understandable that people would worry if this sudden increase in exposure poses any health risk. Fortunately, the evidence so far is reassuring.

Despite the negative evidence to date, in 2011, the International Agency for Research on Cancer classified EMF as a “possible” carcinogen. They have a low threshold for this category, which is rather long. It requires limited evidence of carcinogenic potential in humans and inadequate evidence in animals. This is the, “Probably should do more research just to be sure, but basically don’t worry about it,” category.

EMF and cancer

A new study takes a close look at occupational exposure or electromagnetic fields (EMF), specifically radiofrequency (RF) and intermediate frequency (IF) EMF, and also show no association. The researchers individually rated workers by their exposure to radio frequency and intermediate frequency EMF, and compared 4,000 cases of either meningioma or glioma (the two most common types of brain tumor) and 5,000 controls. They found:

Overall, around 10% of study participants were exposed to RF while only 1% were exposed to IF-EMF. There was no clear evidence for a positive association between RF or IF-EMF and the brain tumors studied, with most results showing either no association or odds ratios (ORs) below 1.0. The largest adjusted ORs were obtained for cumulative exposure to RF magnetic fields (as A/m-years) in the highest exposed category (≥90th percentile) for the most recent exposure time window (1–4 years before the diagnosis or reference date) for both glioma, OR = 1.62 (95% confidence interval (CI): 0.86, 3.01) and meningioma (OR = 1.52, 95% CI: 0.65, 3.55).

Essentially, this is a negative study. The possible correlation between the highest and most recent exposure with brain tumors was not statistically significant. The authors conclude that this possible association deserves further research, which is what authors always say, but this needs to be put into context.

When looking for so many possible correlations, there is going to be a lot of statistical noise. In this study, some of the groups had risks less than one, which if taken literally means that the EMF had a protective effect. No one would conclude this, however. This is just the random noise in the data. Even statistical significance does not necessarily mean an effect is real, but it is a minimum threshold for the data being interesting. In these kinds of studies, and generally, a non-statistical trend should just be treated as negative.

But this also highlights an important aspect of research that is looking for risks – such studies can never prove a risk of zero. There is no such thing as zero risk in science, because that would require complete evidence, which is impractical. So unless you study every human being on the planet, you cannot conclude zero risk, and even then you can just conclude that the risk is less than one in 7.5 billion.

Studies looking for correlations to determine potential risk can only make statistical statements about the probability of risk of a certain magnitude. So in this case the study failed to find a risk from occupational exposure to EMF big enough to be detected by the power of this study, but a smaller risk cannot be ruled out. In other words, any remaining risk must be too small for this study to have detected.

This potentially means that we are never fully done looking for potential risks – we can keep looking for smaller and smaller risks from some exposure. When is the possible remaining risk small enough that we can treat it as no risk? That is a judgement call, but generally we use the background risk as a guide. Once any possible risk is so small that it gets lost in the background risk of just being alive, then it is probably not worth worrying about at that point.

Is EMF there? That’s the question. I think we are close, if we are not already there, and this study brings us closer.

But there is another type of evidence that can be used to address this question also – plausibility. Is there a known mechanism for causing cancer or some other harm, and would we predict based on basic mechanisms that the exposure should convey some risk?

For EMF in the RF and IF range and risk of cancer the answer is that there is no proven plausible mechanism for causing cancer. High frequency EMF carries enough energy that it can break chemical bonds, and therefore cause damage to proteins and DNA. This is a known cancer risk.

Low and intermediate frequency EMF, however, are too low-energy to break bonds. Some have concluded from this that we can eliminate any potential risk on theoretical grounds alone, but I would not go that far. The history of science teaches humility in this regard – even low frequency EMF is a real detectable thing, and carries energy that could potentially have an effect on living tissue, short of breaking chemical bonds.

So I would consider the plausibility of harm as low, but non-zero. Still, this is also reassuring. When we combine low plausibility, with reassuring observational evidence of a lack of correlation, then we are starting to get to the point that we can stop worrying about low frequency EMF.

Unfortunately, I don’t think we are at the point where there is yet enough of a consensus that research will stop. There is still a lot of statistical noise in the research, like in this study, and those who fear a link between EMF and cancer point to that noise as showing a possible risk and demanding more research.

As cell phone use continues to increase, and with each new wave of technology (now with 5G coming), fears of cell phones causing brain cancer continue. I suspect that for years, and probably decades, there will be continuing fear of Wi-Fi, cell phones, and similar technologies causing adverse health effects. Researchers will continue to search for possible links, and the data will probably continue to look like it does now – overall negative, but with the unavoidable randomness that will continue to stoke fears and prompt yet more research.

For now I think it is reasonable to continue to use cell phones and Wi-Fi, reassured that if there is any risk, existing research says it is probably too small to worry about.

Posted by Steven Novella

Founder and currently Executive Editor of Science-Based Medicine Steven Novella, MD is an academic clinical neurologist at the Yale University School of Medicine. He is also the host and producer of the popular weekly science podcast, The Skeptics’ Guide to the Universe, and the author of the NeuroLogicaBlog, a daily blog that covers news and issues in neuroscience, but also general science, scientific skepticism, philosophy of science, critical thinking, and the intersection of science with the media and society. Dr. Novella also has produced two courses with The Great Courses, and published a book on critical thinking - also called The Skeptics Guide to the Universe.