Q: Does consumption of aspartame harm human health?
A: Some research indicates possible negative effects from aspartame, but there’s no definitive evidence linking it to health problems in the general population. Aspartame is safe when consumed within certain limits, according to the U.S. Food and Drug Administration. The daily limit is above the amount people typically ingest.
FULL QUESTION
My husband is driving me crazy with his claims that Diet Coke is going to kill me because it contains the sweetener aspartame. I drink one large Diet Coke (fountain drink) about five times per week. Other than that, I limit my beverages to plain old tap water, which I drink all day. I was diagnosed last year with pre-diabetes and am very careful about my diet. I do not use artificial sweeteners in anything else I eat or drink (water).
Could you please weigh in on this so we can stop the bickering?
FULL ANSWER
The artificial sweetener aspartame was first approved by the U.S. Food and Drug Administration as a food additive in 1974 and as a carbonated beverage ingredient in 1983. It is found in a variety of products — including Diet Coke.
Studies over the years have evaluated whether aspartame is linked to cancer, diabetes, heart disease and a variety of other disorders. There isn’t consistent evidence that aspartame, when consumed under recommended limits, causes health problems. (The exception is for people with a genetic disorder called phenylketonuria, who have trouble processing an aspartame component.)
“[S]cientific evidence has continued to support the agency’s conclusion that aspartame is safe for the general population when made under good manufacturing practices and used under the approved conditions of use,” the FDA says on its website.
On the other hand, there isn’t clear scientific support for any health benefits of aspartame. Some health organizations have endorsed artificial sweeteners as one possible way of reducing sugar consumption, which has known harms. But evidence that artificial sweeteners have long-term effects on weight loss is lacking, and there isn’t evidence they prevent the health problems linked to excess sugar, like diabetes or cardiovascular disease.
“There is no evidence that aspartame is going to ‘kill’ a person,” Lyn Steffen, a nutritional epidemiologist at the University of Minnesota, told us via email, while pointing out gaps in the evidence for any health benefits.
On July 14, the Joint Expert Committee on Food Additives of the World Health Organization and the Food and Agriculture Organization, which assesses whether food additives are safe, came out with its own assessment of aspartame. “Overall, JECFA concluded that there was no convincing evidence from experimental animal or human data that aspartame has adverse effects after ingestion,” the WHO website says.
JECFA reaffirmed that the acceptable daily intake of aspartame is up to 40 milligrams per kilogram of body weight. The FDA’s limit is 50 milligrams per kilogram of body weight. To exceed the lower of these limits, an average-sized adult woman in the U.S., weighing 170.8 pounds (around 77 kilograms), would need to drink more than 10 cans of diet soda a day, assuming at most 300 milligrams of aspartame per can. These limits are established by determining the highest dose tested in animals that is safe and then adding in a substantial cushion as a safety factor.
No ‘Convincing’ Data Linking Aspartame to Cancer
At the same time that JECFA reaffirmed the acceptable daily intake for aspartame, representatives of another WHO organization, called the International Agency for Research on Cancer, came out with yet another assessment of the sweetener, this one specifically focused on cancer.
Both IARC and JECFA concluded that evidence linking aspartame and cancer in humans was not convincing. However, the IARC group was also tasked with assigning aspartame a rating in IARC’s four-tier system for classifying substances’ carcinogenicity.
Based on “limited” evidence for a link between aspartame and liver cancer, IARC declared aspartame “possibly carcinogenic to humans” — leading to widespread media coverage and even a pro-aspartame social media influencer campaign funded by the trade group American Beverage.
The possibly carcinogenic category is reserved for substances with “limited, but not convincing, evidence for cancer in humans or convincing evidence for cancer in experimental animals, but not both,” according to a news release.
Alongside aspartame, this category includes certain pickled vegetables and ginkgo biloba extract, for instance. IARC’s next tier, probable carcinogens, includes red meat and very hot beverages. Examples of carcinogens include processed meat and alcoholic beverages.
For its classifications, IARC does not determine how likely it is that a substance will cause cancer based on a given exposure; it simply determines whether the substance “is capable of causing cancer.”
IARC found “‘limited’ evidence that aspartame causes hepatocellular carcinoma” in humans, the scientists behind the evaluation wrote in the Lancet Oncology. Hepatocellular carcinoma, or HCC, is the most common form of liver cancer.
The IARC scientists identified three studies looking at how often people drank artificially sweetened beverages and whether they eventually got liver cancer. These studies found a small increase in liver cancer risk associated with artificially sweetened drinks in some instances, while failing to find any association in others.
For one European study, researchers asked nearly half a million people in the 1990s about their soft drink consumption and tracked their cancer status for an average of about 11 years. They found that each additional artificially sweetened drink per week was associated with a 6% increased risk of HCC over the course of the follow-up period. They did not find any increased risk for other liver cancer types.
It’s possible some component of the artificially sweetened beverages was behind the increased liver cancer risk, the authors of the European study wrote, or led to some other problem that then led to liver cancer. But the study also showed that people with diabetes or obesity — which are liver cancer risk factors — are more likely to choose these artificially sweetened beverages over sugar-sweetened beverages. And it showed that people who drank more soft drinks of any type had more unhealthy diets, consumed more sugar and calories, and drank more alcohol.
The study authors adjusted for self-reported diabetes status and people’s dietary habits, but it’s possible the increased liver cancer risk was caused by some factor other than people’s soda consumption.
Another study analyzed cancer rates in around half a million people, including around 50,000 people with diabetes, who completed dietary surveys as part of two studies in the 1990s. Researchers followed these people through 2011 or 2017. They found an association between drinking artificially sweetened soda and a 13% increased risk of liver cancer in people with diabetes, but only during the first 12 years of follow-up. There was no association between liver cancer and artificially sweetened sodas in people without diabetes.
“Why increased AS [artificially sweetened] soda consumption would be related to liver cancer among persons with diabetes isn’t clear,” the study authors wrote. They said that some research has found an association between artificial sweeteners and increased abdominal fat, which is associated with liver cancer. Other research has indicated that artificial sweeteners are associated with changes to the microbiota, or the microbes living in a person’s gut.
The third study followed around a million Americans, who reported their beverage consumption in 1982 and were followed through 2016. The study did not show any significant association between liver cancer deaths and artificially sweetened beverages, except among men who had never smoked.
The IARC scientists wrote that the three studies were “of high quality” but that the possibility remained that either chance, bias or some confounding factor explained the associations between liver cancer and aspartame. Therefore, they concluded the evidence that the aspartame caused the cancers was limited.
They also identified studies that found associations between aspartame and other cancer types. But they said that the associations were not “consistent across all available studies” and concluded that evidence was inadequate to link aspartame with other cancer types.
IARC also found there to be limited evidence aspartame causes cancer in animals and limited mechanistic evidence for how aspartame would cause cancer, if it did.
Katherine A. McGlynn, an epidemiologist at the National Cancer Institute, said that another recent study, which came out after the JECFA and IARC analyses, did not find an association between consuming artificially sweetened beverages and liver cancer risk. This study followed around 100,000 postmenopausal U.S. women, who answered questions about beverage consumption in the 1990s and early 2000s, for a median of nearly 21 years. “So the evidence of an aspartame-liver cancer link, at the current time, is very limited,” McGlynn told us in an email.
She explained that major risk factors for HCC include “chronic infection with hepatitis B virus, chronic infection with hepatitis C virus, consumption of foods contaminated with aflatoxin B1, excessive consumption of alcohol, tobacco smoking and a group of related metabolic conditions.” These metabolic conditions, which include, obesity, type 2 diabetes, metabolic syndrome and non-alcoholic fatty liver disease, “have become increasingly more important as risk factors in the past few decades,” she said.
A statement on the FDA website says that the agency “disagrees with IARC’s conclusion that these studies support classifying aspartame as a possible carcinogen to humans,” explaining that FDA scientists found “significant shortcomings” in the studies cited in the report.
“Aspartame is one of the most studied food additives in the human food supply,” the statement says. “FDA scientists do not have safety concerns when aspartame is used under the approved conditions.”
Artificial Sweeteners Have Uncertain Benefits
Even if there isn’t convincing evidence Diet Coke is deadly, there is reason to question whether artificial sweeteners are serving their intended purpose.
While JECFA focused on aspartame’s safety and IARC focused on its carcinogenicity, other groups have aimed to figure out whether it should have a role in a healthy diet.
Some organizations endorse artificial sweeteners as one possible tool for reducing sugar intake. According to American Diabetes Association guidelines, people with diabetes and those at risk for diabetes should “replace sugar-sweetened beverages (including fruit juices) with water or low calorie, no calorie beverages as much as possible.” The guidelines say replacing sugary drinks can help manage levels of glucose in the blood, which is important for people with diabetes, and also reduce risk for heart and metabolic disease.
Use of these sugar substitutes in place of sugar “may reduce overall calorie and carbohydrate intake as long as there is not a compensatory increase in energy intake from other sources,” the guidelines say.
In a 2018 science advisory, American Heart Association researchers wrote that low-calorie sweetened beverages may be a helpful alternative for adults “who are habituated to a sweet-tasting beverage and for whom water, at least initially, is an undesirable option.” However, the advisory indicated it was preferable to switch to plain or carbonated water without any sweetener.
A WHO public health guideline, released in May, for the general nondiabetic population more strongly advised against artificial sweeteners. “WHO suggests that non-sugar sweeteners not be used as a means of achieving weight control or reducing the risk of noncommunicable diseases,” the guideline reads. This recommendation was based on “evidence of low certainty overall,” the guideline authors wrote.
There is evidence from randomized controlled trials that using nonsugar sweeteners leads to lower body weight in the short term, WHO scientists wrote. But they said that most randomized trials were very short, taking place over three months or less, and called results from the few longer-lasting trials “inconsistent.”
The Dietary Guidelines for Americans, published by the U.S. Department of Agriculture and Department of Health and Human Services, also conclude that low- and no-calorie sweeteners, when used as a sugar replacement, “may reduce calorie intake in the short-term and aid in weight management, yet questions remain about their effectiveness as a long-term weight management strategy.”
Randomized controlled trials do not show an impact of artificial sweeteners on diabetes- or cardiovascular disease-related markers, such as A1C, fasting insulin or glucose levels, blood pressure or blood lipid levels, according to the WHO guideline recommending against nonsugar sweeteners.
Some nonrandomized studies, in fact, found an association between nonsugar sweetener consumption and increased risk of type 2 diabetes, stroke and high blood pressure. The WHO authors said that aspartame might theoretically affect cardiovascular and metabolic health by changing a person’s perception or reaction to sweetness, changing their eating behaviors, causing release of metabolic hormones or other substances in the body, or altering their gut microbes.
However, the WHO authors said that their recommendation against nonsugar sweeteners “could result in potential undesirable effects” if it led people to consume more sugar, rather than simply reducing their consumption of sweetened substances and drinking more water.
For someone used to getting caffeine from sweetened beverages, water might not be an acceptable alternative. The American Institute for Cancer Research recommends unsweetened tea or coffee. The Centers for Disease Control and Prevention also endorses unsweetened tea or coffee as an alternative to energy drinks, which can have sugar and other potentially harmful ingredients alongside caffeine.
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