The largest scientific study yet by sample size investigating the link between cell phone use and cancerous tumors in the central nervous system -which surveyed some 358,403 adult cell subscribers age thirty and over in Denmark over a 17 year period and compared them to all non-subscribers – has concluded that “there were no increased risks of tumours of the central nervous system, providing little evidence for a causal association.”
Still, the results of the study, published in the British Medical Journal on Thursday, note that a “a small to moderate increase in risk for subgroups of heavy (cellphone) users” remains to be determined in further study.
“Our study provides little evidence for a causal association, but we cannot rule out a small to moderate increase in risk for subgroups of heavy users,” said Patrizia Frei, of the Institute of Cancer Epidemiology in Copenhagen, Denmark, one of the paper’s authors, the Associated Press reported.
The study is actually the third follow-up of a Danish study that was originally undertaken in 1982, comparing cancer risk of 420,095 subscribers who signed up for mobile phones when they were first available in the country. The original study lasted until 1995 and found no evidentiary support for “an association between use of these telephones and tumors of the brain or salivary gland, leukemia, or other cancers.”
The second update, in 2002 found that “Among long-term subscribers of 10 years or more, cellular telephone use was not associated with increased risk for brain tumors… and there was no trend with time since first subscription.”
The newest study only bolstered those findings. As the latest paper’s authors noted in their discussion of the results: “Importantly, there was no increase of glioma in the temporal lobes in long term subscribers, as the temporal lobe has been described as the region of the brain with highest absorption of energy emitted from mobile phones.”
The latest study update did find a slightly increased, but statistically insignificant, correlation between male cell phone users and gliomas, a type of tumor that originates in the brain. Interestingly, the “the incidence rate ratio was highest in the shortest term users (1-4 years)” and there was a decreased risk for longer term cell phone use. “. In women, there was no association between mobile phone subscription and glioma regardless of duration.”
As for the incidences of meningioma, another type of brain tumor that develops from the meninges, protective linings of the brain and spinal cord, the researchers actually found a “reduction in risk of 22% for male subscribers… but again no indication of dose-response relation.”
However, the researchers noted that there was potential that they miscategorized some users as being cell phone users who weren’t and vice versa (putting non cell phone users into the group of 358,403 adult subscribers), because they only counted the number of subscriptions, which isn’t necessarily demonstrative of use. I.e., A person may regularly use a cell phone over a long period of time and not be a subscriber, whereas a subscriber might never use their phone (finding it continually borrowed by the non-susbcriber)!
There was another big caveat to the latest, reassuring data: As for the decreasing sample size (420,095 to 358,403 adults) in the latest update, the researchers noted that a portion the study’s participants died from various causes, and that “For those who had died, data on exposure were collected from relatives up to 11 years after death. No validation of this approach was conducted, making it impossible to assess the impact of the likely and potentially large recall bias.”
And yet, the study remains the largest one of cell phone users taken over the longest period of time, providing some reassurance in the face of the World Health Organization’s alarming recategorization in May of cell phones as Category 2B risks, “Possibly carcinogenic to humans,” alongside banned pesticide DDT, lead, exhaust, pickled vegetables and coffee, among other substances.
At the time, a working group of 31 scientists analyzing a collection of studies under the World Health Organization’s International Agency for Research on Cancer (IARC) said that the radiofrequency electromagnetic fields produced by cell phones could pose “an increased risk for glioma.”
But on Friday, in response to the October 20 update to the Danish study, the IARC said that it wasn’t about to reconsider the reclassification, further saying that the findings of its working group weren’t necessarily contradictory with the Danish results, noting that it did not have access to the Danish update at the time it made its recommendation in May. “These are new results that were not available at the time,” the IARC wrote.
The IARC continued:
“The studies to date do not permit to rule out a relationship between mobile phone use and risk of brain cancer although the evidence is limited… Avoiding frequent use of mobile phones, particularly in children, or using hands-free sets can reduce exposure while waiting for future research to provide a more definitive answer on the possible carcinogenicity of radiofrequency electromagnetic fields…
“The Danish cohort study has no information on amount of mobile phone use and consequently cannot investigate risk in the subgroup of heaviest users. Therefore it confirms the overall Interphone findings of no association, but with reduced potential for bias. It does, however, leave open the possibility that there is a small increase in heavy users. All studies have in common that risk only becoming apparent after 15-20 years of use could not be investigated.”
Hence, the lack of an impetus to reclassify cell phones again from Category 2B.
That said, there is of course remains a fierce, ongoing debate around the potential cancer risk posed by cell phone radiation, especially in terms of the metaresearch, or studies of previous studies. In July, in fact, a group of international researchers called the largest international study of cell phone users flawed and said that there was increasing evidence that cell phones did not cause cancer.
A group of activists from several countries on Thursday preemptively deemed the Danish study “seriously flawed,” expressing their misgivings collectively in a release posted on the website ElectromagneticHealth.org.
According to Alasdair Philips, a self-described “expert” on electromagnetic radiation and advocate on tougher cell phone restrictions, wrote:
“This study only looks at 7% of the Danish population who had a personal cellphone subscription for at least one year during the period 1987 to 1995. It ignores corporate subscribers (the heaviest users then) and the researchers have no data at all on cellphone use since 1995 so the extra 86% of the population who started to use a cellphone since 1996 were left in the “non subscriber part of the population. This study uses seriously flawed data to make a flawed analysis and should be condemned as misleading spin.”
Similarly, Devra Davis, PhD, masters of public health, cancer epidemiologist and President of Environmental Health Trust, an activist group that has also called for cell phone restrictions, added: “By extending an earlier analysis on the same group of cellphone users this new report provides unsurprising, biased and misleading conclusions.”
We’ve reached out the Danish study’s authors to obtain their response to these critiques and will update when receive a response.
