A Danish study involving 358,403 people over an 18-year period found no evidence of an association between long-term cellphone usage and the risk of brain or CNS (central nervous system) tumors. The researchers, from the Danish Cancer Society and the International Agency for Research on Cancer (IARC) reported in the BMJ (British Medical Journal) that theirs is the largest study ever made to investigate whether there might be a link between long-term cellphone usage and cancer risk.
The study was funded by the Danish Strategic Research Council, the Swiss National Science Foundation, and the Danish Graduate School in Public Health Science. No funds came from the mobile phone industry or companies that supply the industry.
Mobile phone usage has grown enormously over the last ten years - in 2010 there were over 5 billion subscriptions globally, the authors wrote. An ever-growing concern has been whether such communication devices eventually raise the risk of developing tumors in the central nervous system.
Global mobile phone subscribers per country from 1980-2009
The central nervous system or CNS is the part of the nervous system that includes the brain and spinal cord. It is one of the two major divisions of the nervous system - the other being the peripheral nervous system (PNS) which is outside the spinal cord and brain and connects the CNS to sensory organs, such as the ear and eye, and other organs, as well as muscles, glands and blood vessels.
Central Nervous System (2) consists of the brain (1) and spinal cord (3)
The researchers explained that prior studies that set out to determine whether cellphone usage affected tumor risk have been inconclusive, especially with regards to long-term use. Some of the case control studies were found to be flawed, while others were undermined by bias. The IARC (International Agency for Research on Cancer) recently classified radio frequency electromagnetic fields as potentially carcinogenic to humans. Cellphones emit radio frequency electromagnetic fields.
A Danish study involving 420,095 Danish cellphone subscribers who were tracked from 1982 to 1995 and then again with follow-ups in 1996 and 2002, is the only cohort study to look into cellphone usage and cancer risk.
This large study was unable to find any link between long-term mobile phone usage and brain and nervous system tumors.
Researchers, led by the Institute of Cancer Epidemiology (part of the Danish Cancer Society) continued monitoring the cellphone subscribers up to 2007.
They focused on Danes aged at least 30 years who were born in Denmark after 1925. They divided them into two groups, those who had been subscribers since 1995 and people who had a cellphone before 1995. They gathered data from the Danish phone network operators as well as the Danish Cancer Register.
Below are some highlighted details of their findings:
- 10,729 nervous system tumors were reported from 1990 to 2007.
- CNS tumor rates among long-term cellphone users (at least 13 years usage) were nearly the same as for those with no cellphone.
- There was no overall increase of any type of tumor risk for long-term cellphone users, compared to those with no cellphones
"The extended follow-up allowed us to investigate effects in people who had used mobile phones for 10 years or more, and this long-term use was not associated with higher risks of cancer.
However, as a small to moderate increase in risk for subgroups of heavy users or after even longer induction periods than 10-15 years cannot be ruled out, further studies with large study populations, where the potential for misclassification of exposure and selection bias is minimised, are warranted."
Accompanying EditorialProfessors Anders Ahlbom and Maria Feychting, from the Karolinska Institute, Sweden, wrote that this new study provides reassuring news. However, they added that monitoring of long-term cellphone users should continue.
They explained that this study has two key advantages over any previous ones:
- It used a computerized cohort that was followed passively on registries. There was no need to contact individuals, thus avoiding the risk of non-response and selection bias.
- Rather than using retrospective questionnaires or interview information, it used digitized subscriber information gathered from the telephone operators. This avoids a recall bias which had undermined previous studies.