WHO declares aspartame "possibly carcinogenic." Here's what to know about the artificial sweetener.

The World Health Organization has declared aspartame, a common artificial sweetener used in thousands of products, to be "possibly carcinogenic to humans" — while also noting that "safety is not a major concern" in the quantities people would normally consume.

WHO's International Agency for Research on Cancer, or IARC, categorized the sweetener in Group 2B on the basis of "limited evidence for cancer in humans," specifically for hepatocellular carcinoma, a type of liver cancer, according to a news release.

"Cancer is one of the leading causes of death globally. Every year, 1 in 6 people die from cancer. Science is continuously expanding to assess the possible initiating or facilitating factors of cancer, in the hope of reducing these numbers and the human toll," Dr. Francesco Branca, director of the department of nutrition and food safety at WHO, said in a statement Thursday. "The assessments of aspartame have indicated that, while safety is not a major concern at the doses which are commonly used, potential effects have been described that need to be investigated by more and better studies."

Reuters first reported last month that the decision was expected.

In addition to IARC's categorization, the U.N.'s Joint FAO/WHO Expert Committee on Food Additives, or JEFCA, also provided a review on what this means for people's risk, maintaining its existing guidance on acceptable daily intake amounts. 

"Our results do not indicate that occasional consumption should pose a risk to most consumers," Branca added in a press briefing. "We're not advising companies to withdraw products nor are we advising consumers to stop consuming altogether. We're just advising a bit of moderation."

Robert Rankin, president of the Calorie Control Council, an international association representing the low- and reduced-calorie food and beverage industry, said in a statement to CBS News that JEFCA's review reaffirms the overwhelming body of evidence that aspartame is safe.

"To assert otherwise is misleading, inaccurate, and fear mongering to the nearly 540 million people globally living with diabetes and millions of others managing their body weight who rely on and/or chose products that contain low- and no-calorie sweeteners such as aspartame," Rankin said.

He added the IARC is not a regulatory agency or food safety authority. 

"IARC looks for substances that could potentially cause cancer without considering actual dietary intake, and has found many things, such as drinking hot water and working at night, to be probably carcinogenic. It is not only wrong, but potentially damaging to certain populations to position IARC's report alongside true scientific and regulatory agencies like JECFA, the Food and Drug Administration, and the European Food Safety Authority."

What is aspartame?

Aspartame is an artificial sweetener 200 times as potent as regular granulated sugar that is used in thousands of products on grocery store shelves, from sodas and drink mixes to low-cal condiments and desserts. 

Aspartame entered the market as a low-calorie sweetener in 1981 and has been approved by the U.S. Food and Drug Administration for use in food products, with the agency concluding the additive is "safe for the general population." 

• Aspartame products: Here's a list of popular foods and beverages with the sweetener

"Aspartame is one of the most studied food additives in the human food supply," the FDA says. "To determine the safety of aspartame, the FDA has reviewed more than 100 studies designed to identify possible toxic effects, including studies that assess effects on the reproductive and nervous systems, carcinogenicity, and metabolism." 

What is a carcinogen? 

The National Institute of Health's National Cancer Institute defines a carcinogen as "any substance that causes cancer." Carcinogens can occur naturally in the environment or may be generated by humans, the NIH explains, and typically work by interacting with a cell's DNA to produce mutations.

The IARC's designation of "possibly carcinogenic to humans" means the group believes there is "some evidence that it can cause cancer in humans but at present it is far from conclusive." More than 320 other items, ranging from gasoline exhaust to aloe vera to working in the textile industry, share that classification.

To put things in perspective, another 220 substances have been identified as definitive or probable carcinogens for humans, based on stronger evidence of a connection to cancer.

"Exposure to a carcinogen does not necessarily mean you will get cancer. A number of factors influence whether a person exposed to a carcinogen will ultimately develop cancer," the NIH's National Human Genome Research Institute's website notes.

How much aspartame is safe to consume? 

The FDA established an acceptable daily intake (ADI) level, or amount of a substance considered safe to consume each day over the course of a person's lifetime, for each of the six sweeteners approved as food additives. 

For aspartame, the ADI is 50 milligrams per kilogram of body weight per day per the FDA's ruling, and 40 milligrams per the U.N.'s guidance.

"The average 150 lb. person would need to consume about 14 12-oz cans of diet beverages or about 74 packets of aspartame-containing tabletop sweetener every day over the course of their life to raise any safety concern," Rankin said in his statement. "Obviously, that level of consumption is not realistic, recommended, nor is it ‎aligned with the intended use of these ingredients."  

For the general public, there's "no immediate need" to worry about WHO's findings or classifications, Dr. Ernest Hawk, vice president and head of the division of cancer prevention and population sciences at The University of Texas MD Anderson Cancer Center, told CBS News.

"Their strongest signal is to scientists suggesting that more high-quality research is needed," he added. "Only after much more research is done will we be able to determine if aspartame or other similar agents are associated with convincing cancer risks."

Elizabeth Napolitano contributed to this report.

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• Health
• Aspartame
• Cancer
• World Health Organization