Every time I see a headline proclaiming cell phones cause cancer, I cringe. In nearly every case, the study is almost always flawed, in some cases because the results are based on a limited time frame in which results are extrapolated, or because the testing was on animals, or exposure lengths times were accelerated.
These cell phone/cancer studies all are hampered by the lack of a large enough control group in real world conditions tracked over a long enough period of time for the results – i.e. cancers to appear – to have any validity.
We now have such results.
A Danish study has found absolutely, positively no indications that cell phone usage cause cancer. Or, more scientifically, cell phone users contracted cancers just as often as non-cell phone users.
HOORAY!
Except apparently some Debbie Downers deign to disagree.
Why are Danes different?
Why is the Danish cell phone/cancer study valid where previous ones were flawed?
Longevity.
The most recent study results, which tracked Danish cell phone use between 1990-2007, are actually an update of a 2001 report in the Journal of Radiological Protection, which tracked users from 1982-1995. That gives us 30 years of data. (Denmark launched cell phone service in 181, two years ahead of the U.S.)
But if cell phones didn't become available until 1983, how and why would the Danes start tracking cell phone usage before anyone had one?
In Denmark, folks are issued national ID numbers, and the cell phone companies use these ID numbers to identify subscribers. As a result, the Danish researchers could easily break the population into cell phone users and non-cell phone users, and break subscribers into length-of-usage groups.
Here are the exact results and conclusions as published in an abstract in the most recent edition of the British Medical Journal (we replaced the symbol for "greater than or equal to" symbols with words):
Results 358,403 subscription holders accrued 3.8 million person years. In the follow-up period 1990-2007, there were 10,729 cases of tumours of the central nervous system. The risk of such tumours was close to unity for both men and women. When restricted to individuals with the longest mobile phone use — that is, greater than or equal to 13 years of subscription — the incidence rate ratio was 1.03 (95% confidence interval 0.83 to 1.27) in men and 0.91 (0.41 to 2.04) in women. Among those with subscriptions of greater than or eqaul to 10 years, ratios were 1.04 (0.85 to 1.26) in men and 1.04 (0.56 to 1.95) in women for glioma and 0.90 (0.57 to 1.42) in men and 0.93 (0.46 to 1.87) in women for meningioma. There was no indication of dose-response relation either by years since first subscription for a mobile phone or by anatomical location of the tumour — that is, in regions of the brain closest to where the handset is usually held to the head.
Conclusions In this update of a large nationwide cohort study of mobile phone use, there were no increased risks of tumours of the central nervous system, providing little evidence for a causal association.
WHOOPEE!
I think.
Not so fast
As scientific folks often do, there has been some blowback from these optimistic, non-threatening results, not surprising considering the preponderance of previous cell phones-cause-cancer results. (Finding cell phones cause cancer has become a cottage industry – "Ignore Cell Phones-Cause-Cancer Reports.")
One admitted fly in the Danish study ointment is the study couldn't track actual usage, as in how many hours a day some folks spend on their phone. For instance, the researchers admit the study couldn't – and, therefore, didn't – break out business users, who are on their phones a lot more than the rest of us.
One protester also noted only a study that tracked "millions…followed for decades" could be considered valid.
You can read more from the dissenting voices at this blog posting at PsychCentral.com.
But the Danish study tracked nearly 400,000 users in each study for a total of 30 years. I'm not saying I know more than these PhDs about how to interpret and study statistical data – I don't (I did study statistics in college, though) – but how will the results of millions of people differ significantly from 400,000? And isn't 30 years "decades"? And at what point does the different usage patterns of such a massive number of cell phone users tracked for so long simply average out?
While I guess this cell phone/cancer issue is unlikely to be fully settled scientifically, and since I am more-or-less a casual cell phone user (for conversation, anyway, and I always use headphone), I'm buoyed by the Danes, as I often am.
And if you are a casual cell phone user dogged by lingering cell/cancer paranoia, hopefully you will be buoyed, too.