Aspartame Declared ‘Possible’ Carcinogen. Here’s What That Really Means

The artificial sweetener aspartame is now considered “possibly carcinogenic to humans,” declared the International Agency for Research on Cancer (IARC), which evaluates substances’ risk of causing cancer, late on Thursday EDT. The agency specifically found that consumption of artificially sweetened beverages was associated with an increased risk of a type of liver cancer called hepatocellular carcinoma.

The ruling does not mean you need to stop consuming all aspartame-containing products, nor does it change the acceptable daily intake put forth by the World Health Organization (WHO). In a separate ruling released at the same time, the Joint Food and Agriculture Organization/WHO Expert Committee on Food Additives (JECFA), which evaluates the levels of exposure to food additives that pose a risk, found there was no convincing evidence for harm with aspartame consumption below the current acceptable daily intake limit of 40 milligrams per kilogram of body weight. That limit was established by JECFA in 1981. For a 70-kilogram (155-pound) person, it’s equivalent to about 14.5 cans of Diet Coke.

The rulings leave consumers with the confusing message that aspartame could possibly cause cancer but that consuming less than the currently recommended limit is probably not a big risk. Nevertheless, both groups called for more research to assess any potential harms of consuming the popular sweetener.

“The working group classified aspartame as possibly carcinogenic to humans—that is, group 2B—based on limited evidence for cancer in humans,” said Mary Schubauer-Berigan, acting head of the IARC Monographs program, in a press briefing on Wednesday. “The IARC classification reflects the strength of the scientific evidence as to whether an agent can cause cancer in humans, but it does not reflect the risk of developing cancer at a given exposure level.”

IARC is a WHO agency. Based on available data, the committee categorizes substances as group 1 (“carcinogenic to humans”), group 2A (“probably carcinogenic to humans”), group 2B (“possibly carcinogenic to humans”) or group 3 (“not classifiable as to its carcinogenicity to humans”). IARC put aspartame in group 2B based on “limited” evidence that it causes cancer in humans. There was also limited evidence it causes cancer in laboratory animals and limited mechanistic evidence that it shows key characteristics of a human carcinogen.

The increased liver cancer risk finding was based on three studies of four large cohorts in the U.S. and in 10 European countries, according to Schubauer-Berigan.

IARC concluded the evidence of human carcinogenicity was “limited” because the agency was not able to rule out all other factors that could explain the results. It also could not rule out reverse correlation—that people who have other risk factors for cancer may be more likely to consume foods or drinks sweetened with aspartame. In addition, there aren’t many long-term data on aspartame consumption because it has only been incorporated into foods since the mid-1970s.

JECFA concluded that “there’s no convincing evidence from experimental or human data that aspartame has adverse effects after ingestion within the limits established by [the] previous committee, which is the acceptable daily intake of 40 [milligrams] per kilogram body weight,” said Francesco Branca, director of the department of nutrition and food safety at the WHO, in the news briefing. JECFA analyzed studies of cancer-causing genetic mutations in both living subjects and in lab-grown cells, but the investigations gave conflicting results and did not find evidence of such toxicity, he said. The committee also did not find evidence linking aspartame to other diseases risks, except for one paper that showed a risk of type 2 diabetes. The analyzed studies were not sufficient to justify changing the recommended daily limit, Branca said.

Should people who consume aspartame-containing foods or drinks change their behavior? That depends on why you are consuming nonsugar sweeteners. At the briefing, Branca noted that the WHO recently stated that long-term consumption of artificial sweeteners for weight loss is not effective. “If consumers are faced with the decision of whether to take cola with sweeteners or one with sugar, I think there should be a third option considered, which is to drink water instead and to continue to limit the consumption of sweetened products altogether,” he said. “This is particularly important for young children,” who are developing lifelong taste preferences.

IARC rulings are famously cautious—the agency has previously declared everything from aloe vera to pickles to cell phones to be possible carcinogens. Angelo Moretto, a professor at the department of cardiothoracic and cardiovascular sciences and public health at the University of Padua in Italy, and his colleagues wrote in the online publication the European Scientist that the IARC Monographs are like the supercomputer Deep Thought in Douglas Adams’s novel The Hitchhiker’s Guide to the Galaxy: In that book, Deep Thought’s answer to the question of “Life, the Universe, and Everything” is “forty-two.” Yet no one seems to remember what the question itself was.

Like Deep Thought, “the ‘42’ answer that IARC has for everything is ‘carcinogenic’ because its pronouncements are limited to: carcinogenic, probably or possibly carcinogenic to humans, or ‘I don’t know,’” Moretto and his colleagues wrote. “But as another famous line from The Hitchhiker’s Guide to the Galaxy tells us, ‘Don’t Panic.’”