A recent peer-reviewed article evaluated the reliability of the available literature investigating possible links between aspartame and cancer and the results are in: studies linking aspartame to cancer scored as “not reliable” according to an internationally recognized grading system for scientific research.
How the review was designed
The publication “Systematic review and evaluation of aspartame carcinogenicity bioassays using quality criteria” by Haighton et al., which appeared in Regulatory Toxicology and Pharmacology, compared research from different sources looking at aspartame and cancer. In addition to considering the findings of these studies, the new publication took a further step back and analyzed the credibility of studies researching aspartame’s purported link to cancer.
In conducting the literature review, researchers down-selected studies based on specific criteria to “…identify all animal cancer studies of aspartame and critically assess the findings of each study based on a quality appraisal of the study design, methodology, conduct, and reporting.” These studies were assessed against the Klimisch grading system that ranks the reliability of study findings based on how well or poorly a study was designed.
About the Klimisch Code Grading System
The Klimisch Code was developed in 1997, and has since been used to assess study reports for inclusion in the International Uniform Chemical Information Database, and has recently been promoted in Europe to be used for evaluating study reports in ingredient approval applications under the European Union’s (EU) REACH regulation, which addresses potential impacts of chemicals on both human health and the environment.
The Klimisch grading system uses four codes:
- “Code 1” means “reliable without restriction”*
- “Code 2” means “reliable with restrictions”
- “Code 3” means “not reliable”
- “Code 4” means “not assignable”
How studies scored
Ultimately, nine studies from three organizations/researchers were considered.
One organization received Klimisch Code 3 “not reliable”:
- Ramazzini Institute – three animal lifetime studies which linked aspartame to cancer. These studies have been scrutinized by global regulatory agencies for having several deficiencies, as noted by Haighton et al.,:
- Age of lab animals prone to cancer – The studies spanned the lifetimes of the animal subjects. Since risk and incidence of cancer increases inevitably with age, the Ramazzini Institute studies, which conducted necropsies in animals that died or were terminated near end of life, do not meet current research study standards.
- Species of lab animal prone to disease – In addition, for mouse studies reporting an increased incidence of liver tumors and long tumors, Swiss mice were used, which have a high background incidence of both tumor types. In their rat study, there was a lack of randomization of the animals into control and test groups and the Ramazzini Institute used its own rat strains, which were noted to have a very high incidence of infection.
Two organizations received Klimisch Code 2 “reliable with restrictions”:
- National Toxicology Program (NTP) from the US Department of Health and Human Services, with three transgenic mice studies – which concluded that aspartame is safe.
- Searle – three two-year-long studies, which were reviewed by the US Food and Drug Administration (FDA) and the European Food Safety Authority, also finding that aspartame is safe.
NOTE: While the Searle and NTP studies did not receive a Code 1, the Searle studies were conducted before the U.S. Food and Drug Administration (FDA) and Organisation for Economic Co-operation and Development (OECD) published specific standards. The NTP studies were conducted using transgenic mouse models, for which there is not a specific guideline.
Further conclusions of the review
The researchers further note that the studies used to prove the safety of aspartame support the basic biological process the ingredient undergoes. Once consumed, aspartame is broken down in the gut to aspartic acid, phenylalanine and methanol, which are all metabolized via well-characterized metabolic pathways. The authors note no reason to suggest aspartame has carcinogenic potential.
Scientific research on aspartame is essential to ensure that its use, which has been approved in over 90 countries, does not pose a threat to individuals or public health. For this reason, research is thoroughly evaluated not only for study findings, but on how reliable those findings are based on the quality of study design.
* In order to receive a Code 1, studies must be conducted strictly in accordance with internationally accepted test guidelines and laboratory practices. Several guidelines are available to help researchers ensure their studies receive a Code 1, including FDA’s Redbook and the OECD’s guidelines for testing carcinogenicity and studies that combine chronic toxicity and carcinogenicity.