A World Health Organization agency said on Thursday that aspartame, an artificial sweetener commonly used in diet drinks and low-sugar foods, may cause cancer.
However, a second WHO committee remained steadfast in its assessment of a safe level of aspartame consumption. According to some calculations using the panel’s standard, a person weighing 150 pounds could avoid a cancer risk but still drink about a dozen cans of diet soda a day.
A WHO agency’s statement of a cancer risk associated with aspartame marks the first time the prominent international body has publicly spoken out about the effects of the near-ubiquitous artificial sweetener. Aspartame has been a controversial ingredient for decades.
The International Agency for Research on Cancer, or IARC, said it based its conclusion that aspartame is a possible carcinogen on limited evidence from three observational human studies, which found the agency linked consumption of artificially sweetened drinks to an increase in cases of liver cancer. at levels well below a dozen cans a day. It warned that the results could potentially be skewed toward the profile of people drinking higher amounts of diet drinks and called for further research.
Still, people who consume large amounts of aspartame should consider switching to water or other unsweetened beverages, said Dr. Francesco Branca, Director of the WHO Department of Nutrition and Food Safety.
But, he added, “Our results do not indicate that occasional consumption should pose a risk to most.”
Concerns about rising global rates of obesity and diabetes, as well as changing consumer preferences, have led to an explosion of sugar-free and low-sugar foods and drinks. Aspartame, one of six sweeteners approved by U.S. regulators, is found in thousands of products, from packs of Equal to sugar-free gum, diet soda, tea, energy drinks, and even yogurt. It is also used to sweeten various pharmaceutical products.
The U.S. Food and Drug Administration, which approved aspartame decades ago, issued uncharacteristic criticism of the global agency’s findings on Thursday, reiterating its longstanding stance that the sweetener is safe. In a statement, the FDA said it “disagrees with IARC’s conclusion that these studies support the classification of aspartame as a possible human carcinogen.”
The FDA also said that “the fact that aspartame is labeled by WHO as ‘possibly carcinogenic to humans’ does not mean that aspartame is actually associated with cancer.” The FDA declined to make any of its experts available for interviews to discuss the agency’s specific concerns.
But the salvo against the international organization would surely spark further debate in Europe – where the sweetener is still considered safe – and renew the review in the United States. And the dueling global agencies’ rulings are likely to confuse consumers.
The WHO. has occasionally fallen out of line with other authorities on potential cancer risks, such as glyphosate, and later led to a finding that it was dangerous to human health. The international body’s indication of a link between cancer and that ingredient in Roundup, a herbicide, became the springboard for lawsuits against the makers of the herbicide.
Around the world, the powerful beverage industry has fought long and hard against any regulatory or scientific finding linking the use of artificial sweeteners to risks of cancer or other health problems. Aspartame is just the latest battleground for multinational corporations to face new studies or possible links to health risks.
“Aspartame is safe,” Kevin Keane, interim president of the American Beverage Association, said in a statement. He cited WHO’s dueling announcements, selecting the second panel, the Joint Expert Committee on Food Additives, to conduct a concurrent review and leave the recommended daily allowance unchanged. It also deemed the evidence for cancer in humans “inconclusive”, according to a WHO summary.
“After a thorough evaluation, the World Health Organization finds aspartame safe and ‘not a sufficient reason to alter the previously established acceptable daily intake,’” said Mr. Keane. “This strong conclusion strengthens the position of the FDA and food safety agencies from more than 90 countries.”
Coca-Cola referred questions to the American Beverage Association and PepsiCo did not respond to requests for comment.
The safety of sugar substitutes, including the decades-old scientific dispute over the use of saccharin in the diet drink Tab, has come under heavy scrutiny. Once linked to bladder cancer in rats, Congress ordered further study of saccharin. Since then, according to the FDA, 30 studies have shown that the rodent results did not apply to humans; US officials have removed saccharin from a list of possible carcinogens. More recently, other sweeteners have come under scrutiny for their association with potential health risks.
At the center of the aspartame dispute are rodent studies from 2005-2010 by Italy-based researchers that showed a link to cancer. The FDA has dismissed the long-discussed studies as “compromised.”
Dr. William Dahut, chief scientific officer of the American Cancer Society, who led one of the key studies on which the WHO relied, said the findings should be considered alongside the WHO’s report earlier this year that artificial sweeteners did not help achieving weight loss. or protection against other chronic conditions.
He said there is now little evidence to suggest that a daily Diet Coke would increase cancer risk, adding that “more research is needed.” Overall, he said, the science was more definitive about reducing cancer risk by avoiding tobacco, alcohol, processed meats and being overweight.
The IARC said it could not rule out the possibility that the studies linking aspartame to liver cancer were the result of chance or other factors associated with diet soda drinking.
The WHO Cancer Office has four categories: carcinogenic, probable carcinogenic, possible carcinogenic and no classification. Those levels reflect the strength of the science rather than how likely the compound is to cause cancer.
The other WHO group on food additives recommended that daily consumption should be less than 40 milligrams of aspartame per kilogram of body weight – slightly lower than the suggested US level of 50 milligrams.
The FDA said it estimated that a person weighing 132 pounds would need to consume 75 packets of aspartame sweetener to reach the exposure threshold of potential risk.
For the review of aspartame, the IARC convened 25 cancer experts from 12 countries in Lyon, France, to conduct the review of existing studies. It concluded there was limited evidence for cancer in humans based on three studies linking artificially sweetened drinks to increases in hepatocellular carcinoma, the most common type of liver cancer.
A 2016 study was led by WHO officials, which looked at nearly 500,000 people in Europe who were followed for about 11 years. The study tracked participants’ juice and soft drink intake and its relationship to liver and bile duct cancer. It examined those who drank artificially sweetened soda and found that each additional serving of diet soda per week was associated with a 6 percent increased risk of liver cancer.
A US study published last year by researchers from Harvard, Boston University and the National Cancer Institute examined the consumption of sweetened drinks reported by people on questionnaires and cancer registries. Researchers found an increased risk of liver cancer in people with diabetes who said they consumed two or more artificially sweetened sodas per day. That study found no increase in liver cancer in diet soda drinkers who did not have diabetes.
A third study, led by the American Cancer Society, examined the consumption of drinks sweetened with sugar and artificial sweeteners and data on cancer deaths. It found a 44 percent increase in liver cancer in men who never smoked and drank two or more artificially sweetened drinks a day. Even adjusted for high body mass — itself a risk factor for cancer — the men had a 22 percent increase in risk, data in a supplement to the study shows.
The American Beverage Association, which represents Coca-Cola and PepsiCo, has clearly said that the WHO’s food additive panel — not the cancer experts — should be the leading authority evaluating aspartame.
In recent weeks, the beverage industry trade group has funded a new coalition led by Alex Azar, an appointee of former President Donald J. Trump, and Donna Shalala, an appointee of former President Bill Clinton. Both Mr. Azar and Ms. Shalala were former secretaries of the Ministry of Health and Human Services. In an op-ed in Newsweek earlier this month, the two embraced the FDA’s position on aspartame’s safety, calling the agency “the world’s gold standard for independent regulators.”
The trade group had previously challenged another assessment of aspartame’s possible links to cancer in California. In 2016, a state commission discussed aspartame review but went no further.
California officials this week said the state could review WHO’s latest decision.
In addition to aspartame, the WHO’s cancer organization has considered other possible carcinogens as seemingly benign, such as Ginkgo biloba extract and aloe vera leaf extract, to more concerning ones, such as gasoline exhaust and perfluorooctanoic acid, the most common industrial chemicals known as per- and polyfluoroalkyl substances, or PFAS, which have recently been subject to multibillion-dollar settlements for drinking water contamination.
By deeming aspartame a possible carcinogen, the IARC also fell into one of the central controversies of aspartame research. It concluded that there was some evidence of cancer in laboratory animals based on studies conducted by the Ramazzini Institute in Italy, citing the finding of the group of increased tumors in aspartame trials from the mid-2000s. Based on concerns about the methods and interpretations of the group, however, the findings were considered limited.
For its part, the Ramazzini Institute said in 2021 that its work on aspartame was validated and that its previous findings “came ferociously attacked by the chemical manufacturing and processed food industry and by their allies in regulatory agencies.”
Dr. Responding to questions about the need for an IARC review at a press conference on Wednesday, WHO’s Branca said 10 million people die from cancer each year. “So there’s a social problem that our organization had to respond to,” he said.
He said the results showed a clear need for further high-quality research.
“We’ve kind of raised a flag here, indicating that we need to bring a lot more clarity to the situation,” said Dr. Branca. “It’s not something we can dismiss at this point.”
Julie Creswell contributed reporting.