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Aspartame a Possible Carcinogen: What Does It Mean?

After aspartame was officially classified as a "possible carcinogen" last week by an agency of the World Health Organisation (WHO), people may be wondering what it means. Experts in the UK and elsewhere have suggestions for how to advise patients.

Aspartame has been given a Group 2B classification based on data from three studies that assessed the link between intake of the sweetener and primary liver cancer, a classification that meant the evidence was "limited", the International Agency for Research on Cancer (IARC) pointed out. 

The evidence that aspartame caused primary liver cancer, or any other cancer in humans, is "very weak" and there's "not much evidence" to suggest that the association is causal, said Paul Pharoah, professor of cancer epidemiology, Cedars-Sinai Medical Center, Los Angeles.

"The public should not be worried about the risk of cancer associated with a chemical classed as Group 2B," he reassured.

Other things in the Group 2B category include mobile phone use and petrol engine exhaust fumes, commented Oliver Jones, professor of chemistry at RMIT University.

Dr Duane Mellor, a registered dietitian and senior lecturer at Aston University, told the Science Media Centre that this classification places the sweetener with "things like aloe vera and caffeic acid".

Hazards and Risks

Professor Jones stressed that two terms need to be understood: "hazard", which 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," he said. "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 low, most of us don't think about it — even though the risk is not zero."

The IARC only looked at hazard, he pointed out, which in this case meant 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," he pointed out.

"Sunlight is a hazard as it can cause cancer, but the risk depends on the amount of sunlight and whether we use protection, explained Gunter Kuhnle, professor of nutrition and food science at the University of Reading. "Likewise, even if aspartame causes cancer at very high amounts, there is no risk when consuming it at the amounts that are permitted in foods," he reiterated.

No Change in Consumption Recommendation

In the expert summary, published in Lancet Oncology, the working group — which included the IARC and the Food and Agriculture Organization (FAO) Joint Expert Committee on Food Additives (JECFA) — reaffirms the acceptable daily intake of 40 mg/kg body weight for aspartame, and concluded that there was "no sufficient reason to change this".

A spokesperson explained that because "a can of diet soft drink contained 200 or 300 mg of aspartame, an adult weighing 70 kg would need to consume more than 9 -14 cans per day to exceed the acceptable daily intake, assuming no other intake from other food sources".

Professor Kuhnle welcomed the opinion as it "ends the speculation about the safety of aspartame" and made it "very clear" that there was "no cause for concern" when consumed at the current amounts.

Moderation and Further Research Needed

Sir David Spiegelhalter, emeritus professor of statistics at the University of Cambridge, expressed frustration, lamenting that the IARC reports were "getting a bit farcical". 

"In spite of IARC's conclusion that aspartame was 'possibly carcinogenic to humans', which got lots of media attention, another expert committee (JECFA) that actually investigates the magnitude of any risk found "no convincing evidence from experimental animal or human data that aspartame has adverse effects," he said.

"As they have said for 40 years, average people are safe to drink up to 14 cans of diet drink a day, which is about an old gallon — about half a large bucketful," he pointed out.

"What this does not mean," stressed Dr Mellor, "is we should start consuming aspartame or other non-nutritive sweeteners more often."

Dr Francesco Branca, director of the department of nutrition and food safety at WHO, highlighted that while aspartame's safety is "not a major concern at the doses which are commonly used", potential effects had been described that need to be investigated by more and better studies.

Prof Robin May, chief scientific adviser at the Food Standards Agency (FSA), said that the JECFA report supported the FSA's view that aspartame was safe to consume at current permitted use levels, and welcomed the call for more and better studies to help "increase understanding of this potential issue".

"We're not advising consumers to stop consuming [aspartame] altogether," clarified Dr Branca. "We're just advising a bit of moderation."

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