Selasa, 31 Mei 2011

The World Health Organization, cell phones, and cancer—what's actually going on


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Today, I was surprised to see posts popping up on Twitter implying that the World Health Organization's International Agency for Research into Cancer had declared radiation from cell phones to be a cancer risk. As you've read here before, and as sources like the National Cancer Institute have reported, the evidence linking cell phone use and cancer risk is actually pretty slim. So I was waiting to hear about some new study or analysis. Instead, it looks like this is really a story about context.

If you don't have the context, it's easy to look at the headlines and assume that the WHO just told you to stop using your cell phone. But, add context, and the news looks very different. In fact, with context in place, it appears the WHO isn't saying cell phones are dangerous, and isn't saying anything you haven't heard before.

Science blogger Ed Yong works for Cancer Research UK. He wrote up a very nice explanation of what the WHO announcement really means.
It means that there is some evidence linking mobile phones to cancer, but it is too weak to make any strong conclusions. Specifically, IARC's panel said that the evidence that mobile phones pose a health risk was "limited" for two types of brain tumours - glioma and acoustic neuroma - and "inadequate" when it comes to other types of cancer.
The Chairman of the group, Dr Jonathan Samet, said, "The conclusion means that there could be some risk, and therefore we need to keep a close watch for a link between cell phones and cancer risk."
IARC classifies different things according to whether they are likely to cause cancer, from tobacco to viruses to certain jobs. They are the gold standard for this sort of thing. They have five possible categories of risk:
Group 1 is the highest, reserved for things like smoking, asbestos, alcohol and so on. It means that there's extremely strong evidence that the thing in question causes cancer.
Group 2A includes things that are "probably carcinogenic to humans". Here, the evidence is "limited" in humans, but "sufficient" from animal studies.
Group 2B - this is the one that mobile phones now fall under - means something is "possibly carcinogenic to humans". It means there is "limited evidence" that something causes cancer in people, and even the evidence from animal studies is "less than sufficient". Group 2B means that there is some evidence for a risk but it's not that convincing. This group ends up being a bit of a catch-all category, and includes everything from carpentry to chloroform.
Basically, this is where we start talking about semantics, and the difference between official, bureaucratic categories and how people actually talk about risk in everyday life. When you hear someone say, "Using your cell phone probably won't give you cancer. The evidence supporting that idea is very weak," they are, more or less, saying the same thing that the World Health Organization is saying. Only the WHO has also added the (very reasonable) assertion that more research is needed if we want to say anything definitive about cell phones and cancer.

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