We live in an age geared towards spectacle. In order to attract our attention, content providers create ever more dramatic headlines to steal our focus (if only for a moment). Earlier this week, the World Health Organization (WHO) released their findings on a certain food product and here are some of the ways that news was reported:
As you can see, the headlines just get more and more dramatic as you go on.
While they are all based in a nugget of a fact, there is a certain sleight-of-hand going on. Most people will only note the headline. It's easier to remember just the lede and forget about any level of nuance buried deep within the story. The real truth remains well hidden.
These reports started with the WHO's International Agency for Research on Cancer (IARC). This team of scientists actually has a narrow task.
The IARC is an organization of scientists, not policy makers. It publishes monographs to identify hazards and sift them into five piles: group 1 (carcinogenic), group 2A (probably carcinogenic), group 2B (possibly carcinogenic), group 3 (not classifiable), and group 4 (probably not carcinogenic.) Group 1 includes processed meat, and also asbestos. Also alcohol (boo!) and sunlight (yup!).Identifying hazards involves looking at existing data—lots and lots of it—to do essentially a meta-analysis of studies already out there. And it’s relatively objective.
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What the IARC doesn’t do—and where things get a lot fuzzier—is risk assessment, or figuring out the danger to humans in the real world. Risk assessment involves looking at different scenarios, finding out real-world exposure levels, and weighing possible benefits. (Useful drugs like Tamoxifen—used to treat breast cancer—are also carcinogens, for example.) Those factors can vary from person to person, country to country.
When IARC looked at the evidence to see whether or not substances in processed meats caused cancer, they found clear and convincing evidence that it could. But there is a critical distinction missing from all of the headlines:
Here’s the thing: These classifications are based on strength of evidence not degree of risk.
Two risk factors could be slotted in the same category if one tripled the risk of cancer and the other increased it by a small fraction. They could also be classified similarly even if one causes many more types of cancers than the other, if it affects a greater swath of the population, and if it actually causes more cancers.
So these classifications are not meant to convey how dangerous something is, just how certain we are that something is dangerous.
But they’re presented with language that completely obfuscates that distinction.
Group 1 is billed as “carcinogenic to humans,” which means that we can be fairly sure that the things here have the potential to cause cancer. But the stark language, with no mention of risks or odds or any remotely conditional, invites people to assume that if they specifically partake of, say, smoking or processed meat, they will definitely get cancer.
To give you some idea of how that might change the reality of their findings, here is another tidbit:
That latest press release offers only this by way of numbers: “The experts concluded that each 50 gram portion of processed meat eaten daily increases the risk of colorectal cancer by 18 percent.” But without context, that information is useless—increases by 18 percent over what?—and says nothing about how processed meat compares to other Group 1 carcinogens like smoking or asbestos.
And what are those odds?
The scientific evidence linking both processed meat and tobacco to certain types of cancer is strong. In that sense, both are carcinogens. But smoking increases your relative risk of lung cancer by 2,500 percent; eating two slices of bacon a day increases your relative risk for colorectal cancer by 18 percent. Given the frequency of colorectal cancer, that means your risk of getting colorectal cancer over your life goes from about 5 percent to 6 percent and, well, YBMMV. (Your bacon mileage may vary.) “If this is the level of risk you’re running your life on, then you don’t really have much to worry about,” says Alfred Neugut, an oncologist and cancer epidemiologist at Columbia.
I don't think I'm giving up bacon any time soon!
Here are some articles for reference:
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