Does Aspartame Cause Cancer? Here’s What an Expert Wants You to Know

Following the recent decision of a World Health Organization (WHO) agency to classify aspartame as "possibly carcinogenic to humans," many may be left wondering whether it is safe to use the popular artificial sweetener.

What exactly does this mean, and should you be worried? It's a question nutritionists and oncologists here at the Smilow Cancer Hospital get asked often, and the answer is not as clear as you might hope.

What is aspartame?

Aspartame is one of several artificial sweeteners approved for use in the United States. It may be found as a standalone sweetener (it accounts for nearly 75% of artificial sweetener sales in the United States) or in many prepared food and beverage products.

Aspartame vs. sugar: What’s the difference?

Sucrose is the scientific name for table sugar. It may be found naturally in foods such as fruits, vegetables and grains. It is also extracted and refined from sugar cane or sugar beet to be added as a sweetener to processed foods such as candy, ice cream, breakfast cereals, baked goods, soda and other sweetened beverages.

On the other hand, aspartame is an artificial sweetener that is chemically modified in a lab to be a substitute for sugar. It is low-calorie and about 200 times sweeter than sugar, which allows much less of it to be used to achieve the same level of sweetness. It is found most often in diet or sugar-free beverages, but it is also used in more than 6,000 other products, including food items (diet or sugar-free gelatin, jams, ice cream and other foods that do not require high heat, as aspartame can’t withstand high temperatures), as well as pharmaceutical and personal care products (chewing gum, sugar-free cough drops, some medicines and toothpastes).

Does aspartame cause cancer?

Concerns surrounding the safety of artificial sweeteners have been around for years. However, available evidence on cancer risk in humans has not yet yielded clear, conclusive or consistent results.

The July decision from the WHO's International Agency for Research on Cancer (IARC) to classify aspartame as possibly carcinogenic was based on limited evidence from three studies that found a link to a particular kind of liver cancer. However, none of the studies could rule out other factors as a potential cause for an association between aspartame and cancer risk. This panel also found limited evidence from animal or experimental studies, and limited evidence for how aspartame may possibly cause cancer. It is important to note that this and all IARC classifications assess the strength of evidence as to whether something can cause cancer, not how likely it is to cause cancer.

Simultaneously, the Joint Food and Agriculture Organization of the United Nations and World Health Organization Executive Committee on Food Additives (JECFA) also met to update their evaluation regarding the safety of aspartame at its June/July meeting. The purpose of this committee is to conduct risk assessments to determine the likelihood of harm when exposed to a particular substance at a specified level. They concluded there is no convincing evidence from experimental or human studies that aspartame has negative effects after ingestion, and that it is not possible to establish a link between aspartame exposure and the development of cancer at levels typically consumed.

In an unusual move, the U.S. Food and Drug Administration took issue with the IARC ruling when it was announced, releasing a statement that said it disagreed with the agency's conclusions on aspartame.

"The FDA disagrees with IARC’s conclusion that these studies support classifying aspartame as a possible carcinogen to humans," the agency said in a statement at the time. "FDA scientists reviewed the scientific information included in IARC’s review in 2021 when it was first made available and identified significant shortcomings in the studies on which IARC relied."

"Aspartame is one of the most studied food additives in the human food supply," the agency added. "FDA scientists do not have safety concerns when aspartame is used under the approved conditions."

Below is a chart from the U.S. Food and Drug Administration that lays out how much sweetener is safe to consume, by type, on a daily basis:

Source: U.S. Food and Drug Administration

Is aspartame bad for you?

While questions remain about whether aspartame is linked to cancer, the sweetener should be avoided by anyone with phenylketonuria, a rare genetic disorder that prevents the body from breaking down phenylalanine, which is an amino acid component of aspartame. Meanwhile, the jury is still out on any connection between aspartame or other artificial sweeteners and cardiovascular disease, overweight/obesity, diabetes, migraines and allergies.

The JECFA included an evaluation of aspartame specifically in relation to the development of type 2 diabetes and cerebrovascular disease in its recent risk assessment, but did not find convincing evidence of a connection. The IARC and WHO recommends further research on aspartame in relation to cancer and other health conditions, a position that is supported by the American Cancer Society and American Institute for Cancer Research.

Food additives, including aspartame, are regulated by the FDA in the United States, which also sets the maximum amount that is considered safe to consume per day. The acceptable daily intake for aspartame is 50 milligrams per kilogram of body weight per day. To put this into perspective, an adult weighing 132 pounds would need to consume 75 packets of aspartame per day to reach this level. While the JECFA recommends a slightly lower daily intake at 40 milligrams per kilogram per body weight per day, this still equates to up to 14 cans of diet soda per day.

Bottom line

There is not sufficient evidence at this time to suggest that aspartame causes cancer in quantities approved for use in food. While further research is warranted to explore any possible link between aspartame, cancer risk and other health conditions, it is considered safe in amounts typically consumed.

It’s important to mention that the recent classification by the IARC also does not imply that beverages and foods sweetened with sugar are better. High intake of added sugar is linked to a number of conditions, including type 2 diabetes and obesity, which are also known to increase cancer risk. If looking to decrease your intake of sweetened beverages overall, water infused with fruit or herbs may be a flavorful change, decreasing sweetener added to your morning coffee or adding flavor with spices such as cinnamon or nutmeg can go a long way.