This article was originally posted in the Montreal Gazette.
If you’ve never heard of the International Agency for Research on Cancer (IARC), I wouldn’t be surprised. But I can almost guarantee you’ve heard of its work.
You might remember a few years back when multiple headlines claimed hot dogs were as bad as cigarettes. Depending on where you lived, it might have been hamburgers or smoked meat. It’s not, of course. Smoking is far, far worse for you.
But now the IARC is at it again and according to leaked documents, on July 13 it will declare the artificial sweetener aspartame a possible carcinogen. There was predictable online panic, with equally alarming headlines. But it’s not actually true.
In order to put this story in context, you have to understand what the IARC is and what it actually does. Its mission is to review the studies done on a given product and determine how strong the evidentiary link to cancer actually is. It reviews lab data, animal studies, observational research and any randomized trials that may exist.
Sometimes the data is strong and sometimes the data is wishy-washy, contradictory and uncertain. The IARC’s grading system assigns products to Group 1 (carcinogenic), Group 2A (probably carcinogenic), Group 2B (possibly carcinogenic) and Group 3 (not classifiable).
When something gets listed in Group 2B, as possibly carcinogenic, that usually means human data is lacking or inadequate and the agency is making an extrapolation from animal or in-vitro lab data.
Over the years, the IARC has labelled many things as possibly, probably or definitely carcinogenic. Of note, there’s nothing currently listed in Group 4 as not carcinogenic. And while “possibly carcinogenic” still seems worrying, it is instructive to look at other things that have received similar or worse designations.
Aloe vera is listed as possibly carcinogenic. Higher up on the list as probable carcinogens in Group 2A are drinking hot liquids, working as a barber and doing shift work. At the apex, in Group 1, the definite carcinogens include things like birth control pills and tamoxifen (the medication used to treat breast cancer).
At this point, the careful reader is probably confused. Allow me to explain. Birth control pills have estrogen in them. Estrogen increases the risk of breast cancer. Both of those statements are undeniably true. So when the IARC committee reviews the evidence on birth control pills, it concludes the link between them and cancer is clear and unambiguous, hence the designation as a Group 1 carcinogen.
But most people would point out that birth control pills contain low doses of estrogen and pose virtually no risk for the millions of women who use them regularly. Similarly, tamoxifen is an effective breast cancer treatment and has saved untold numbers of lives. Yet it does carry a small increased risk of uterine cancer. That’s true, but is clinically of little concern given its overall reduction of cancer mortality.
The absurdity of these contradictions can be explained once you understand what the IARC is doing. It evaluates hazard, not risk. In this context, hazard reflects whether something is linked to cancer, not how dangerous that something is. (In statistics, hazard has a different definition, but that’s a story for another day.) So the IARC only cares whether estrogen is linked to breast cancer or if tamoxifen is linked to uterine cancer. It doesn’t evaluate whether they actually pose a risk, because that’s not its mandate.
As for aspartame to be listed in Group 2B, the data is far from convincing. Also, most people will not consume enough of it to achieve anything resembling dangerously high blood concentrations. Estimates are you would have to drink at least 12, if not closer to 36, cans of diet soda per day to get that much aspartame in your system. Stay under that threshold and you should be fine.
