Focus on Food Safety: Aspartame and cancer ‘risk’

The International Agency for Research on Cancer (IARC) has deemed aspartame as a “possible carcinogen”. This is a concern for manufacturers formulating with this popular non-caloric sweetener. When a manufacturer hears the term, “possible carcinogen,” it becomes a moment of alarm for food safety, but what does ‘possible’ mean within the context of this report?

It’s important to reflect on the power of words in hazard and risk assessment. Media coverage of IARC’s assessment does not do justice to the science that was conducted, and the actual evidence presented.

IARC is a United Nations World Health Organization (WHO) agency tasked with monitoring cancer risks within the human environment. IARC uses a classification system with four levels. Group 1 is “Carcinogenic to Humans,” and this grouping has either sufficient evidence to prove carcinogenicity in humans, or strong evidence in humans supported by sufficient evidence in experimental animal models, along with a known mechanism for carcinogenicity.

Group 2 is split into two subgroups. Group 2A is “Probably carcinogenic to humans,” which has limited evidence of carcinogenicity in humans but sufficient evidence in experimental animals or inadequate evidence in humans but sufficient evidence in animals along with a strong understanding of a mechanism of carcinogenesis, or limited evidence in both humans and animals but a similar molecular structure to a compound already listed in Groups 1 or 2A.

Group 2B is “Possibly carcinogenic to humans,” meaning there is limited evidence in humans and less than sufficient evidence in animals, or inadequate evidence in humans but sufficient evidence in animals or inadequate evidence in humans and less than sufficient evidence in animals but supporting evidence from mechanistic and other data.

Group 3 is “Not classifiable as to its carcinogenicity to humans,” and this group does not imply that compounds are not carcinogenic or safe, it just means that more research is required, because evidence is inadequate in humans and animals, the mechanisms do not support carcinogenicity, or the agent does not fall into normal classifications.

Risk vs. hazard

The power of words is vital. In almost all modern IARC monographs, there is a preamble that’s typically overlooked by media. The term, “carcinogenic risk,” in IARC monographs series is taken to mean that an agent is capable of causing cancer. The monographs evaluate cancer hazards despite the historical presence of the word, “risks,” in the title. Risk is not the same as hazard, but IARC has chosen to use the word, “risk,” in their documentation. A hazard is something that can cause harm, while risk is the likelihood and the impact that a hazard will cause harm. IARC does not actually evaluate risk, only hazard.

In the most recent IARC report, the basis of evidence was three observational studies using consumption data for artificially sweetened beverages as the proxy for aspartame consumption, then looking for causes of morbidity and mortality within that group. Liver cancers, in particular hepatocellular carcinoma, were observed with higher frequency in groups consuming larger amounts of artificially sweetened beverages. IARC’s report itself discusses how this observation is correlational, and not necessarily causative.

IARC works in tandem with the Joint Expert Committee for Food Additives (JECFA), a U.N. Food and Agriculture Organization and WHO joint committee focused on the risk assessment of food additives. JECFA not only looks at hazard, but also typical dietary intake and food applications to understand exposure to consumers. JECFA published a joint commentary, and notably, they chose to not change the acceptable daily intake of 0-40mg/kg body weight in humans, or the estimated equivalent of nine to 14 cans of aspartame sweetened soda per day, assuming no other dietary sources.

Hepatocellular carcinoma is most frequently caused by hepatitis infection, heavy alcohol consumption, cirrhosis, cigarette smoking, several genetic diseases and non-alcoholic steatohepatitis. Non-alcoholic steatohepatitis is typically caused by diabetes, high cholesterol, and blood triglycerides. Obesity and the stress it causes on the body may be a key factor. Artificially sweetened and calorie-reduced food products, often containing aspartame, are the default choices of many people experiencing obesity.

When you understand what IARC means from a technical perspective, the term, “possible carcinogen,” does not have the same foreboding as a media report claiming, “aspartame is a possible cancer risk”. IARC takes a precautionary stance in its communications.

Health Canada and FDA are not making any changes to how aspartame can be used following IARC’s report. 

Dr. Amy Proulx is professor and academic program co-ordinator for the Culinary Innovation and Food Technology programs at Niagara College, Ont. She can be reached at aproulx@niagaracollege.ca.

This column was originally published in the October 2023 issue of Food in Canada.