Aspartame a ‘possible carcinogen’ says WHO cancer group

Aspartame — a popular artificial sweetener found in diet sodas, breakfast cereals, medications, toothpaste and much more — will be declared a possible carcinogen next month by the cancer research arm of the World Health Organization (WHO), reports say.

The International Agency for Research on Cancer (IARC) is poised to declare aspartame as “possibly carcinogenic to humans” following review by independent international experts, two sources with knowledge of the process told Reuters Thursday.

The IARC told the Star it “assessed the potential carcinogenic effect of aspartame,” but that it hasn’t researched how likely this harm is to occur, including how much aspartame one can safely consume in a day. That’s being handled by the Joint FAO/WHO Expert Committee on Food Additives (JECFA), a spokesperson for the agency said; both the IARC and JECFA reports will be published on July 14.

Without the JECFA’s risk analysis, it’s hard to say how seriously we should take this report, said David Ma, a professor researching nutrition and cancer at the University of Guelph: “There are safe limits for the consumption of aspartame.”

What’s a “possible carcinogen?”

There are four categories for carcinogens determined by the IARC, ranked in terms of how certain we are the substance can cause cancer. From most to least certain, these are: “carcinogenic to humans,” “probably carcinogenic,” “possibly carcinogenic” and finally “not classifiable as to its carcinogenicity in humans.”

“Possible carcinogens” are when a substance has limited evidence of cancer risk in humans, “sufficient” evidence in animals and “strong” evidence that the substance shares key characteristics with known carcinogens, according to the IARC.

Notably, the ranking doesn’t relate to how dangerous the substance is. The “possible carcinogens” category includes over 300 substances, from lead and gasoline engine exhaust to aloe vera. It also includes species of chlorinated paraffins, a since-banned chemical that was recently discovered in commercial products and toys sold across Canada.

Aspartame has been studied extensively since its inception in 1965. The IARC’s latest findings come after months of screening over 7,000 studies, with approximately 1,300 being included in the final review.

Is aspartame bad for you?

Aspartame may be linked with cancer, but that doesn’t mean it’s necessarily dangerous — it depends how much you consume.

For a 60 kg individual (or about 130 lb), “the threshold for adverse health effects (of aspartame) is something on the order of 12 to 36 cans of diet soda,” Ma said. “That’s a lot — so it’s overall a low risk based on today’s science.”

More specifically, in 1981, the JECFA ranked the acceptable daily intake of aspartame as 40 milligrams per kilogram of body weight per day. With canned diet sodas averaging around 200 milligrams of the sweetener, that’s about 12 drinks a day for a 60 kg individual.

“If you’re having an occasional can of diet soda, I wouldn’t be too worried,” Ma said. “Though I would be very concerned if you are exceeding ten or more drinks per day, consuming some kind of artificial sweetener.”

That said, this figure was based on over 40-year-old data. Whether the JECFA’s recommendations has changed since then will be revealed in July.

While aspartame’s harms are debatable, so too are its benefits, according to Reinhold Vieth, a professor emeritus of nutritional sciences and laboratory medicine at the University of Toronto.

“There is absolutely no evidence that a person is any healthier by consuming products that contain artificial sweeteners in general,” Vieth said in an email to the Star. “ … My family and I have long avoided artificial sweeteners for reasons beyond any awareness of risk of cancer.”

Muddied research on aspartame

Despite the reams of research into the topic, it’s difficult to parse how aspartame might affect us in daily life, Ma said. For example, the amounts of aspartame being tested in the lab may differ wildly from the amounts we consume day-to-day.

“In these research studies, very large amounts are being tested and they may not be equivalent to usual consumption,” Ma continued. “Back to our diet soda analogy, on average someone might only be consuming one (soda) every other day — but in the research study, they might be testing (exposure to the equivalent of) 10 to 20 cans per day.”

This gets especially muddied when dealing with cancer, which often takes years or even decades to develop after exposure.

“There’s still a need for long term studies for determining if something will cause cancer. It takes many years to sort out,” Ma said. “So where a lot of the data comes from is using experimental models and animal models or cell culture, and then trying to extrapolate (to humans).”

Industry pushback

Already, voices from the beverage and sweetener industries are pushing back against the IARC’s findings.

In a press release Thursday, the International Council of Beverages Associations said the agency’s “leaked opinion contradicts decades of high-quality scientific evidence and could needlessly mislead consumers into consuming more sugar rather than choosing safe no- and low-sugar options — all on the basis of low-quality studies. ”

The council then cited a 2022 systematic review by the WHO that found “no significant association” between non-nutritive sweeteners like aspartame and cancer mortality.

“We remain confident in the safety of aspartame given the overwhelming weight of scientific evidence and positive safety determinations by food safety authorities in more than 90 countries around the world,” said the group’s executive director Kate Loatman in the release.

The International Sweeteners Association, whose members include PepsiCo, Mars Wrigley and a Coca-Cola unit, also released a statement saying: “The ISA has serious concerns with preliminary speculation about the IARC opinion, which may mislead consumers about the safety of aspartame.”

Popular items containing aspartame

Aspartame is not limited to all stripes of diet sodas — it’s used as an artificial sweetener in a great many goods, some of which you might not be aware of.

These include: tabletop sweeteners, gum and candies, gelatin, breakfast cereals, ice cream, sugar-free cocoa mix, medications (like cough drops or gummy vitamins), toothpaste and more.

Ma also warns that products containing artificial sweeteners may not list exactly how much of the substance it contains, so shoppers should be wary. But if you’re cooking for yourself and avoiding highly-processed foods, he believes “you have little to be concerned about.”

Consuming aspartame “on occasion is perfectly fine, based on current evidence, but excessive levels is where we might get into trouble,” he continued. “My wife hates this message, but everything in moderation. And I think that applies in this case.”