Why there is little cause for heightened alarm based on these new results
On Friday, May 27th, results from a highly anticipated, $25 million study conducted by the US National Toxicology Program hit the headlines and reignited the well-known debate about the connection between cellphone use and developing brain cancer. Here’s how leading health and life science publication STAT put it:
“A major new [animal] study out this morning finds there’s a connection between cell phone exposure and two types of cancer. The peer-reviewed, longitudinal study — which was conducted by the National Toxicology program — exposed rats to the same type of radiation found in cell phones. Total-body exposure to radiofrequency radiation was tied to higher incidence of gliomas in the brain and schwannomas in the heart, and researchers say there’s likely a direct connection between the two.”
However, as the article (and others that followed) note, there are a number of caveats with this study, which should give pause to drawing any drastic conclusions. NBTS spoke to a number of experts in the field of brain tumor epidemiology and glioma risk and compiled the following:
- The study was done in rats, not humans. The scientific and biomedical research field has consistently found throughout its history that often results in animals do not always translate to humans. Our biology is different.
- Only male rats developed gliomas, and it is curious why female rats did not develop a glioma.
- Not all rats had actual tumors, some of them only had hyperplastic glial changes (i.e. inflammatory changes to the glial cells).
- In only one of six experimental groups of rats was an increased risk for gliomas observed and it was in the group that had a very high dose exposure. The exposure began in-utero and continued throughout life. This dose level is not comparable to real life exposure.
- Only 2-3% of all exposed animals developed a glioma; this was similar to control-group results in previous, similarly-designed studies that have been done on the topic.
- The actual incidence of glioma in general is very low to begin with, and thus the statistical power for this study to make conclusions on very small increases and differences in incidence is low, based on the actual number of rats used in this study. In general, when you want to see very small differences, such as those described in this study, you need much larger numbers of animals than used in this study.
- Recently published studies in humans on incidence trends analysis using U.S.-based cancer registry data found no increases in incidence of gliomas from 2000-2010 (coinciding with the major rise in cellphone use).
- Additionally, other human, observational data collected in earlier, large-scale population-based studies have found limited evidence of an increased risk for developing cancer from cellphone use.
- The authors of this study say their findings, “appear to support” the World Health Organization’s (WHO) conclusion that cellphones are only a “potential carcinogen.”
- The authors of the study note that these are only preliminary findings, and there are still more data to analyze. Thus, there is no telling if the small connection seen to-date will hold over larger studies.
Overall, throughout the years there have been conflicting results about whether cellphones cause brain tumors, because of various study designs, methodology, and sample size –but the prevailing sentiment from experts in this field, was that there is no definitive link…or at least, we could not yet definitively say either way.
Bottom line, this new animal study – despite generating even more mainstream media attention than others in the past have – does little to advance a consensus forward in either direction. As such, the National Brain Tumor Society’s position on cellphone risk remains the same:
“The latest studies have not been able to definitively conclude a direct link between cell phone usage and brain tumors in humans, but it has not been ruled out either. Most of these studies report correlations, and not actual causation, therefore other factors that are hard to account for may be affecting that results. Additionally, many studies in the past have not taken into account the latest technology and change in how cell phones are used. It is also of note that the incidence rate for brain tumors has not increased in the past decade. Thus, without conclusive results, the National Brain Tumor Society can not say that cell phones cause brain tumors, and can only encourage continued further research into this topic. We also would encourage any individuals who are concerned about emissions from their cellular phones to consider using a headset, as per World Health Organization recommendations.”
Further suggested reading:
- The National Cancer Institute’s very detailed page on this issue, including statements from other organizations, including the WHO: http://www.cancer.gov/about-cancer/causes-prevention/risk/radiation/cell-phones-fact-sheet
- A comprehensive article from 2014 on the sum of the evidence to date from Reuters: http://www.reuters.com/article/2014/05/22/us-mobilephone-brain-tumor-idUSKBN0E22AJ20140522
- A CNN story from last year: http://www.cnn.com/2015/07/28/health/cell-phones-brain-tumor-risk-berkeley/index.html