WHO cancer arm deems aspartame 'possible carcinogen,' consumption limits unchanged

The rulings are the outcome of two separate WHO expert panels, one of which flags whether there is any evidence that a substance is a potential hazard and the other which assesses how much of a real-life risk that substance actually poses.

Aspartame is one of the world's most popular sweeteners, used in products from Coca-Cola diet sodas to Mars' Extra chewing gum.

In a press conference ahead of the announcement, the WHO's head of nutrition, Francesco Branca, tried to help consumers make sense of the seemingly conflicting declarations, particularly those who seek out artificial sweeteners to avoid sugar.

In the decisions announced on Friday Geneva time, the International Agency for Research on Cancer (IARC) said aspartame was a "possible carcinogen", its first declaration on the additive. The classification means there is limited evidence that the substance can cause cancer. It does not take into account how much a person consumes.

A separate panel, the WHO and Food and Agriculture Organization (FAO) Joint Committee on Food Additives (JECFA), has that role. After undertaking its own comprehensive review, this body said on Friday that it did not have convincing evidence of harm caused by aspartame, and continued to recommend that people keep their consumption levels of aspartame below 40mg/kg a day. It first set this level in 1981, and regulators worldwide have similar guidance for their populations.

Several scientists not associated with the reviews said the evidence linking aspartame to cancer is weak. Food and beverage industry associations said the decisions showed aspartame was safe and a good option for people wanting to reduce sugar in their diets.

The WHO said that the existing consumption levels meant, for example, a person weighing between 60-70kg would have to drink more than 9-14 cans of soda daily to breach the limit, based on the average aspartame content in the beverages - around ten times what most people consume.

The IARC panel said on Friday it had made its ruling based on three studies in humans in the United States and Europe indicating a link between hepatocellular carcinoma, a form of liver cancer, and sweetener consumption, the first of which was published in 2016. It said limited evidence from earlier animal studies was also a factor, although the studies in question are controversial. There was also some limited evidence that aspartame has some chemical properties that are linked to cancer, the IARC said.

Scientists with no links to the WHO reviews said the evidence that aspartame caused cancer was weak.

'Stevia... a safer alternative to aspartame' - scientist on aspartame

"While it's important that consumers avoid aspartame, they should not replace it with sugar," said Dr Thomas Galligan, principal scientist for food additives and supplements of the US-based Center for Science in the Public Interest (CSPI). "When it comes to beverages, which are by and large the major source of aspartame in the US, water really is your best beverage choice. Unsweetened beverages like coffee and tea can also be good options, but really, water is your best choice. So if you currently drink diet soda, switch to water or unsweetened drinks, or worse comes to worst, drink it sweetened with stevia if you want something that has a sweet taste, that's a safer alternative to aspartame in our opinion."

"This is something that industry, consumers and regulators really need to take notice of," Galligan said. "This is very concerning. CSPI would like to see the industry begin to reformulate its products, use safer alternatives and help consumers avoid and minimize their exposure to aspartame. Similarly, policymakers can also take this very important and authoritative evaluation under consideration and start taking steps to protect consumers as well. CSPI has long recommended that consumers avoid aspartame because of concerns about cancer. So now, IARC, a respected international authority on cancer, is echoing those concerns, classifying this very widely used sweetener as possibly carcinogenic."

The IARC first said aspartame was a "medium priority" for review in 2008. It was nominated for review in 2014 by the CSPI. After the 2014 nomination, aspartame was listed as "high priority" by the IARC "because of its widespread use, lingering concern over its carcinogenic potential, and recent reports of positive findings in studies of carcinogenicity in animals," according to documents published at the time by the agency. But no action was taken until 2022 after aspartame was again nominated for review by CSPI in 2019.

"CSPI has nominated aspartame to be evaluated by IARC on a couple of occasions, most recently in 2019, and that's because IARC is really the authority on these matters," Galligan said. "They are the experts. They really specialize in cancer. And so we knew that IARC could provide much-needed clarity on the link between aspartame and cancer using their scientifically rigorous, comprehensive, transparent and systematic approach to evaluating the evidence, and that's exactly what they've done."

The IARC declined to comment on the lack of action on aspartame for over a decade. The agency updates its priority list every five years, and usually deliberates on many – but not all – of the substances in each period. Some items are reconsidered: coffee, for example, was listed as a possible carcinogen in the 1990s, but taken off the list in 2016.

A recent study on artificial sweeteners came out in March 2022. It was an observational study from France among 100,000 adults and showed that people who consumed larger amounts of artificial sweeteners, including aspartame, had a slightly higher risk of some cancers.

However, the NutriNet-Sante study led by researchers at the University of Paris does not show that the risk was caused by aspartame and critics say its design, based on people self-reporting their real-world consumption of sweeteners, is a limitation. The French researchers declined to comment.

"Self-report bias is a limitation, but that absolutely does not invalidate their findings," Galligan said. "The NutriNet-Sante study performed I think one of the best aspartame exposure assessments of the human studies that I've seen. And they also did find significant positive associations between aspartame exposure and the incidence of certain cancers. So this study was strong for a number of reasons, they had a very large sample size and they used really high quality repeated dietary assessments to calculate the actual dose of aspartame being consumed by their subjects."

Reuters