Monday May 9 2016
Around 4.7 billion people own a mobile phone
"Mobile phones don't increase the risk of brain cancer, 30-year study concludes," the Mail Online reports.
The Australian study found the massive increase in mobile phone use over the past 30 years was not matched by a similar rise in brain cancer cases.
The first official mobile phone call in Oz took place in 1987 by the then Minister of Communication, Michael Duffy. Now, mobile phone ownership rates are estimated to be around 94%.
Despite the explosion in Australian mobile phone ownership, the researchers found no corresponding spike in brain cancer rates. They therefore concluded there was no evidence that mobile phones cause brain cancer.
But the researchers only had the number of Australians with mobile phone contracts to play with – they didn't have any individual data, for example, with information about how often or for how long people had their phones to their heads or, increasingly in the smartphone era, held over their faces.
The study tells us that at a population level, it's unlikely mobile phone ownership is responsible for any moderate or larger increase in brain cancer in Australia. But it doesn't tell us about individual risk patterns.
Despite this uncertainty, when it comes to other risk factors for cancer, such as smoking, poor diet, drinking too much alcohol and lack of exercise, mobile phone ownership is probably not a significant risk to your health.
If you are concerned, read more about the potential risks of mobile phone use.
Where did the story come from?
The study was carried out by researchers from the University of Sydney and the University of New South Wales, Australia. No funding source was mentioned.
It was published in the peer-reviewed journal, Cancer Epidemiology.
The Mail Online coverage was accurate and contains a link to an article by the lead author, which may be of interest to those wanting more information about the background to the study and its possible implications.
What kind of research was this?
This ecological study set out to look for a link between mobile phone ownership and brain cancer incidence since the first mobile phone call in Australia in 1987.
Since the 1980s, mobile phone use has rocketed in most countries, including Australia, where more than 90% of the adult population use them today.
But mobile phones have been dogged by consistent and high-profile concerns that the electromagnetic radiation they give off might cause or contribute to cancer.
The researchers reference several reports showing an alleged link between mobile phone radiation and cancer, but say they had problems with the methods used in these studies, which meant the results were inconsistent and hard to replicate, and so may be wrong.
In an attempt to clear up the controversy, they set out to do a large, long-term study assessing the alleged link, bypassing many of the methodological flaws of previous research.
This sort of study is the most appropriate type to uncover any link between mobile phone ownership and cancer at a country level.
But as it is an ecological study, we need to resist the natural temptation to apply the country-level findings to individuals. We are dealing with averages of large groups, not individual cases.
What did the research involve?
All cases of cancer are recorded in Australia and have been for many decades. The percentage of Australians with mobile phone accounts was obtained from large mobile phone companies and governing bodies.
Putting these two pieces together, the researchers had mobile phone accounts dating between 1987 and 2014, and brain cancer diagnoses of 19,858 male and 14,222 females between 1982 and 2012.
Their analysis looked at whether the rise in mobile phone ownership was linked to a rise in new cases of brain cancer, and they did this separately for different age groups and genders.
The researchers then probed the alleged link in more detail. Assuming a 10-year lag between phone radiation exposure and resulting cancer, they calculated the number of cancer cases they would expect to see if phone radiation caused cancer in a 20-year period, using the best estimates of risk increase from recent studies.
Their assumption was that mobile phones raised the risk of brain cancer 1.5 times for "ever-users" – those who'd used a mobile phone at any point in their lives – and 2.5 times for "heavy users", defined as more than 896 hours of total life use, which represented around 19% of Australians. These risk estimates were informed by previous research.
Using these assumptions, they were able to calculate an expected number of brain cancer cases if mobile phones caused brain cancer and compare it with the number of cases actually observed.
What were the basic results?
Mobile phone use in Australia rose from 0% in 1987 to 94% in 2014. Over a similar time period, 19,858 males and 14,222 females aged 20 to 84 were diagnosed with brain cancer from 1982 to 2012.
Age-adjusted brain cancer incidence rates over this time rose slightly in men but not at all in women. The rise in men was not attributed to mobile phone use.
Assuming mobile phones caused brain cancer, the researchers expected to see much higher rates of cancer than they did.
For example, the actual rate of brain cancer in men was 8.7 cases per 100,000 men, which should have been around 11.7 per 100,000 if the causal theory was true.
Combining men and women of all ages, they expected around 1,867 cases of brain cancer in 2012 if mobile phones were part of the cause (ever-users), but found significantly less: 1,434. The difference was even larger for heavy users: 2,038 expected compared with 1,434 actually observed.
One age group, 70 to 84 years, did show up as having similar expected and observed cases, but the rise in cases started in 1982, before the introduction of mobile phones, leading the researchers to conclude it couldn't be caused by mobiles.
They thought it was probably the result of more access to better cancer diagnosis over time – picking up more cancer cases than in the past – leading to higher rates of cancer overall.
How did the researchers interpret the results?
The researchers concluded that: "After nearly 30 years of mobile phone use in Australia among millions of people, there is no evidence of any rise in any age group that could be plausibly attributed to mobile phones."
This ecological study found an explosion in Australian mobile phone ownership since the 1980s coincided with relatively little change in brain cancer rates, suggesting mobile phone ownership is unlikely to cause brain cancer.
This conclusion is based on assuming there would be a 10-year lag between mobile phone use and cancer, and 1.5 and 2.5 times risk increases due to mobile phone use. Using different assumptions may lead to different conclusions.
The study has many strengths, including its large size, comprehensive information on brain cancer rates over many decades, and research-based assumptions when modelling the expected number of cancer cases – assuming mobile phones do raise the risk of cancer.
What might be less obvious is that the study was more about mobile phone ownership rather than use. While you'd expect the two to be closely linked, it's important to spot the difference.
The data the researchers had was about having a mobile phone contract – they didn't have individual patterns of use in terms of how often the phone was pressed up against users' heads emitting different strengths of radiation, for example.
As such, it's probably wise to use the term phone ownership, rather than phone use – used in the media – when talking about this study.
The study's conclusions are in line with other research quoted by this study, which showed no link between mobile phones and brain cancer.
The big problem with ecological studies are that they don't tell us about individual risk patterns, only about averages of large groups, in this case Australians. This is really useful for public health professionals who deal in population level issues, but less relevant for you and I.
For example, we can't infer from this study, however tempting, that mobile phone use doesn't contribute to brain cancer in some way, as the data simply isn't individualised or detailed enough to find out.
These caveats aside, it would be surprising, given the now massive ownership of mobile phones across the globe, if there was a strong cause and effect association, such as that between tobacco use and lung cancer.
If you are concerned, read more about the potential risks of mobile phone use.