EXPERT REACTION: 'Limited' evidence for cancer risk from common sweetener aspartame

The International Agency for Research on Cancer (IARC) has released its report that classified the sweetener aspartame as a class 2B carcinogen (Possibly carcinogenic to humans). To put this in perspective, hot beverages are in the IARC class 2A (probable carcinogens). This means that IARC feels there is some weak evidence of carcinogenicity despite decades of research that shows no evidence of carcinogenicity in animal models and many studies that have shown no risk for non-Hodgkin’s leukaemia, myelomas, lymphomas, hematopoietic cancer and glioma.

ndeed, the most recent systemic review of non-sugar sweeteners that came out in March found no consistent evidence of carcinogenicity from epidemiological studies. The IARC’s classification was based on three observational studies of liver cancer based on self-reported aspartame consumption.  The data was not consistent between the different studies and given uncertainties about doses and other factors that impact cancer, this finding could be just statistical noise.

Notably, the U.S. Food and Drug Administration disagrees with this new classification, pointing to the enormous evidence of safety. It is important to realise that the IARC rules on any possibility of cancer, and not risk. In terms of risk, the WHO Joint Expert Committee on Food Additives (JECFA) reaffirmed the acceptable daily intake of 40 mg/kg body weight, which translates to around 2.3 to 3.5 litres of diet drink a day.

In short, the evidence of any human risk is very weak indeed, and if you are not going to worry about your risk from a hot cuppa then the aspartame you put in it is even less of a worry.

The IARC has made the assessment that leaked reports over the last few weeks suggested they would and classified aspartame as category 2b, the 2nd lowest level. This means there is insufficient evidence of a link. Other things in this category include mobile phone use and petrol engine exhaust fumes.

This is the first time that the IARC has looked at aspartame and seems to have been prompted by a paper that came out in 2022 that mentioned liver cancer. The IARC expert committee would have reviewed all the available literature when coming to this conclusion, but not done any new research themselves.

There are two terms we need to understand here. The first is ‘hazard’ which just means a possible harm (even if that harm would be very unlikely to occur), and ‘risk’ which is the likelihood of the harm occurring. Think of it like driving a car. There is definitely a hazard; cars crash, and people get injured, and even die, but the risk of that happening when you drive to the shops or take the kids to school is fairly low, most of us don’t think about it - even though the risk is not zero.

Now, the IARC only looks at hazard, which in this case means they just looked to see if there was any evidence that aspartame might be linked to cancer. They do not make an assessment of how likely the hazard is to occur.

The Joint FAO/WHO Expert Committee on Food Additives committee has not changed its safety rating on Aspartame which they set at about 40mg/kg body weight which for a 70 kg adult would mean drinking roughly 17 cans of Diet Coke a day, over a long period. This is consistent will all the major food safety agencies around the world who regularly conduct their own assessments and all classify aspartame as safe at the levels it is used at.

We should also remember that we all exposed to carcinogens every day. It sounds scary but its about risk. Even things that the IARC classifies as class one carcinogens, such as UV light and alcohol, do not cause cancer instantly just because you are exposed to them once. For example, if you get too much sun on the beach in summer you might get sunburn but you’ll recover. If you continually sunbathe with no sun protection then your risk of skin cancer goes up.

In short, I will continue to enjoy my Pepsi Max and I think you can too.

For current consumers of diet drinks, this news isn’t cause for major alarm. Aspartame has been classed in IARC’s Category 2B, which means there’s limited evidence that it might cause cancer, not that it does or is likely to. The work from JECFA confirms that normal levels of consumption appear to be safe.
 
Beyond this focus on aspartame and cancer specifically, we know the use of sweeteners in our food supply is increasing – in Australia for example, the food industry has been turning away from aspartame for some time, with more use of ‘natural’ sweeteners such as Stevia (cite). As governments and consumers have looked to reduce sugar intake, we’re seeing an increase in sweetener use across the food supply – not just in drinks. It's important that we continue to study the long-term effects of this on a range of health outcomes. Given other recent guidance from the World Health Organization that non-sugar sweeteners should not be used as a means of achieving weight control or reducing the risk of heart disease or diabetes, it might still be wise to think about the overall benefits to health (and your wallet) from trading a soft drink habit of any kind for healthier alternatives such as tap water.

The IARC classification and JECFA determination means that aspartame is possibly carcinogenic, if consumed in large amounts. However, recent Australian research suggests the use of aspartame in the Australian food supply is declining and that most Australians are not consuming aspartame at the levels considered unsafe. This classification of aspartame is, however, a timely reminder for Australians to consider the choices they make when it comes to what they eat and drink. 

We know that 2 in 3 Australian adults are living with overweight or obesity, increasing their risk of 13 types of cancers. While ‘sugar-free’ or ‘diet’ drinks containing intense sweeteners might once have been marketed as a means of weight management, recent evidence shows that replacing sugars with intense low-kilojoule sweeteners does not support weight management in the long term and is potentially associated with increased risk of type 2 diabetes and cardiovascular diseases.  

What Australians can do to lower their risk of cancer is maintain a healthy diet with minimal processed foods, be physically active every day for at least 30 minutes, quit smoking and limit their alcohol use. By following these recommendations, Australians can decrease their cancer risk and live long and healthy lives.

IARC has re-analysed old studies and come to the conclusion that the intense sweetener aspartame is “possibly carcinogenic to humans” (Group 2B). The quality of evidence that underpins this assessment (mostly based on rodent studies) is not high and the conclusion can of course by challenged.
 
Regardless, like most things in life, dose matters. The JECFA have reaffirmed the Acceptable Daily Intake (ADI) of 40 mg/kg body weight per day which has been in place in Australia since aspartame was approved for use in foods and beverages in the 1980s. The most recent FSANZ diet exposure assessment determined that the the average Australian consumes less than 10% of the ADI and even the biggest consumers have less than 25% of the ADI”
 
Since this survey was conducted, other intense sweeteners have been approved including “stevia” and “monk fruit”, and have been popular as they are perceived as more natural alternatives.
 
Australian population intakes of aspartame are therefore well below the ADI, and likely to be decreasing due to the popularity of other alternatives. Therefore, even the most avid users are not likely to be at increased risk of cancer from aspartame in Australia.
 
Finally, to put the IARC conclusion into perspective, aspartame will be grouped with other Group 2B foods/additives like pickled (Asian) vegetables, the colour amaranth and preservative Butylated hydroxyanisole (BHA). However, processed meats like ham, bacon and hot dog sausages are classified as Group 1 carcinogens and red meat is classified as Group 2A, indicating that they represent a higher risk for consumers than aspartame.

Aspartame has been classified as possibly carcinogenic to humans by the International Agency for Research on Cancer, World Health Organization.

That means its safety at current doses is not a major concern and we need to do more and better research to understand its effects. To put this in context, the evidence is stronger for the links between alcohol and cancer, or red meat and cancer.

Sugary drinks are the bigger problem. There is good evidence for an association of sugary drinks with diabetes, dental decay, and other chronic diseases. But they have not been reviewed by IARC.

The problem with studying diet drinks containing aspartame is that people may be selecting these products because they are already at high risk of nutrition related disease, and they want to reduce that risk. So it can be difficult to untangle these effects.

We need urgent action to improve our food environment in New Zealand.