Aspartame causes cancer
In 2023, IARC classified aspartame as "possibly carcinogenic to humans" (Group 2B) based on limited evidence, while WHO's JECFA committee simultaneously reaffirmed the existing acceptable daily intake, concluding no need for consumers to change consumption at typical levels.
What we know
In July 2023, two WHO-affiliated bodies published coordinated but distinct assessments of aspartame, a widely used artificial sweetener found in diet sodas, sugar-free gum, and thousands of other processed food products. The International Agency for Research on Cancer (IARC) classified aspartame as "possibly carcinogenic to humans," placing it in Group 2B, based on what IARC itself described as limited evidence from human studies, primarily observational data linking high aspartame consumption to a small increased risk of liver cancer in some cohort studies, along with limited evidence from animal studies and mechanistic data.
It is important to understand what an IARC Group 2B classification does and does not mean. The classification system evaluates the strength of evidence that a substance could cause cancer under some circumstance, not the actual level of risk associated with typical exposure. Group 2B includes several hundred substances and exposures encountered in ordinary life, including aloe vera extract and working night shifts, alongside aspartame. It is a hazard identification, not a risk assessment, and does not by itself indicate that consuming aspartame at normal dietary levels meaningfully raises an individual's cancer risk.
Simultaneously with the IARC announcement, the Joint FAO/WHO Expert Committee on Food Additives (JECFA), which specifically conducts quantitative risk assessment rather than hazard classification, reviewed the same body of evidence and reaffirmed the existing acceptable daily intake (ADI) of 40 milligrams per kilogram of body weight per day, a level that had been in place since 1981. JECFA concluded that this existing ADI provides an adequate margin of safety and that there was no convincing mechanistic or robust epidemiological evidence to lower it. To reach even the ADI, a 70-kilogram adult would need to consume roughly 9 to 14 cans of diet soda daily, well beyond typical consumption patterns for the overwhelming majority of consumers.
The European Food Safety Authority conducted its own comprehensive review of aspartame safety in 2013, examining a large body of toxicological and epidemiological literature, and reached a similar conclusion, that aspartame is safe at current permitted use levels and existing ADI. The FDA has stated that its own review of the available scientific information continues to support the conclusion that aspartame is safe for the general population at estimated exposure levels. The scientific dispute here is real, and the observational studies linking aspartame to liver cancer risk warrant continued research given some inconsistency across study populations, but the overall body of major regulatory and scientific assessment does not support the conclusion that typical aspartame consumption presents a meaningful cancer risk to consumers. Media coverage of the July 2023 announcement often reported the IARC classification prominently while giving less attention to the simultaneous JECFA risk assessment, contributing to public confusion about the practical implications, since a hazard classification without an accompanying dose and exposure context tends to sound more alarming than the underlying evidence supports. Consumers concerned about aspartame can reasonably choose to moderate consumption or select alternative sweeteners as a personal preference, but current major regulatory assessments do not indicate that typical consumption levels of diet beverages or sugar-free products pose a demonstrated cancer risk.
Common claims
- Aspartame was classified as a carcinogen by WHO in 2023Partly true, IARC classified it 'possibly carcinogenic' (Group 2B) based on limited evidence
- Drinking diet soda causes cancerNot supported at typical consumption levels according to WHO's JECFA risk assessment
- The acceptable daily intake for aspartame was lowered in 2023False, JECFA reaffirmed the existing ADI of 40 mg/kg body weight
Evidence hierarchy
All sources
- Aspartame hazard and risk assessment results releasedWorld Health Organization · 2023
- IARC Monographs evaluate carcinogenicity of aspartameInternational Agency for Research on Cancer · 2023
- AspartameEuropean Food Safety Authority · 2013
- Aspartame and Other Sweeteners in FoodUS Food and Drug Administration · 2023