How safe are our cell phones really? The evidence over the years has remained unclear, with the World Health Organization designating cell phone radiofrequency waves as a possible human carcinogen (cancer-causing). In animal studies, some evidence does appear to indicate that radiofrequency waves can cause cancer, with a study from the US National Toxicology Program demonstrating that high exposure in male rats and mice was associated with an increased likelihood of developing tumors in their hearts, brains, and adrenal glands.
Nonetheless, the animal studies demonstrating an increased likelihood of developing tumors are not directly generalizable to cell phone usage in humans. In these studies, the rodents received radiofrequency waves across their entire bodies for many hours a day and for most of their lives, so they received a much higher exposure to radiofrequency waves than most people experience in their everyday life.
To that end, the best way to assess whether or not cell phone usage is associated with cancers, and brain tumors in particular, is to use epidemiological studies in humans. Epidemiological studies are studies in which large datasets of people are examined over a period of time to determine whether or not a certain exposure (in this case, cell phone usage) is associated with a certain disease outcome (in this case, brain tumors).
There are a few different types of epidemiological studies. One type is called a case-control study, in which researchers look at individuals who already have a disease and then compare their history to individuals without the disease. Another type is called a prospective study, in which researchers select a group of participants and track different exposures (such as cell phone usage) over time, not knowing which participants will develop the disease.
A key limitation of case-control studies, however, is that they rely on the patient’s memory, which can be prone to recall bias. For example, brain tumor patients may be more likely to think they had greater cell phone usage than they actually had. For this reason, many epidemiologists consider prospective studies to provide stronger evidence than case-control studies.
Prospective studies examining cell phone usage are limited, but recently, researchers in the UK have published a prospective study in which participants were followed over 14 years to determine whether cell phone use was linked to brain tumors. In this study, participants were recruited between 1996 – 2001 through the UK National Health Service’s breast screening program (because it was a program screening for breast cancer, all the participants were women).
In 2001, the average age of the participants was 59.9, and women were given surveys and answered questions on their medical and lifestyle factors, including their cell phone use. Participants were then separated into several categories based on whether or not they used cell phones and length of cell phone usage. After a period of 14 years of follow-up, 776 156 women out of the original 1.3 million that were recruited reached the trial endpoint and had answered questionnaires on cell phone usage.
The study authors found that across a multitude of different measures, no increases in brain tumors were seen in cell phone users versus non-users. In addition, there were no differences in brain tumor rates between participants that had used cell phones for 10 years or more compared with non-users.
These findings stayed consistent even when separating their analysis to look at specific kinds of brain tumors, such as glioblastomas, a type of brain tumor with the poorest outlook for patients. The study authors concluded that based on their analysis cell phone usage does not increase the risk of brain tumors under usual conditions. Still, the study authors note that a drawback of their study is the lack of analysis on different levels of cell phone usage, as well as how cell phone usage may have changed from the initial recruitment period in the early 2000s until now.
Additionally, future studies may expand on the sample population to include both men as well as women, as this study only included women. While there are questions still to be explored, it appears that for now cell phone users can rest a bit easier knowing that the radiofrequency waves from cell phones are unlikely to cause brain tumors.