Ask the Doctors

Dear Doctor: I've heard that cellphones increase the risk of brain tumors -- and also that they don't. Which is true?

Dear Reader: First, let's look at brain tumors in general. They are classified as either benign or malignant, meaning cancerous. The most common type of benign brain tumor is a meningioma, which arises from the meninges, the outer lining of the brain and spinal cord. The most common type of malignant brain tumor is a glioma, which arises from glial cells that line the individual nerve cells.

Ionizing radiation from nuclear accidents or explosions, radiation therapy, or even too-frequent dental X-rays can increase the risk of brain tumors. This type of radiation can lead to mutations within the DNA, increasing the risk of tumor cells.

Cellphones and cordless phones, on the other hand, emit radiofrequency energy, a form of non-ionizing radiation. This type of radiation has little potential to cause DNA damage. From that perspective, because cellphones produce non-ionizing radiation, their risk of cancer should be pretty low. Now let's check out the data.

A 2015 Swedish study in the Journal Oncology Reports looked at meningiomas diagnosed between 1997 and 2009. People with meningiomas filled out questionnaires asking about their use of cellphones, home cordless phones and analog phones (phones attached to a wire). The authors also asked whether the patients had placed the phone toward one ear or the other, or used both ears equally.

The authors found no statistical difference between mobile phone use and cordless phone use when compared to analog phones. However, those with the greatest amount of cordless and cellphone use had a higher rate of meningiomas compared to those with the lowest amount of cordless and cellphone use.

The interesting aspect of this is that those who frequently used analog phones also had more meningiomas than those who used analog phones less frequently. So this research carries the possibility of recall bias, in which someone with a disease may overly represent a possible risk factor.

A 2017 analysis of many studies, published in the journal Neurological Sciences, found no overall association between cellphone use and brain tumors. Rather, the authors found that many studies on the topic were methodologically flawed.

The authors did note that the higher-quality studies showed a correlation between cellphone use and brain tumors. The authors also concluded that in the higher-quality studies, long-term use of mobile phones was linked to an increase in the risk of brain tumors. Long-term use was defined as greater than 10 years, or more than 1,640 hours.

Another 2017 analysis, published in the International Journal of Occupational Medicine and Environmental Health, reached a similar conclusion.

It's difficult to make judgments based on this data. There does appear to be some evidence that more than 10 years of cellphone use may increase the risk of brain tumors. Yet the potential for recall bias means the data aren't irrefutable. Nonetheless, I would recommend being conscious of the amount of time you spend with a cellphone or a cordless phone against your head. Luckily, we can now communicate through a Bluetooth device, reducing whatever risk there may be.

One encouraging note? Rates of both benign and malignant brain tumors decreased in the United States between 2009 and 2013.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

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