A sweetener used in Diet Coke and other sugar-free fizzy drinks may cause cancer, the World Health Organization (WHO) is reportedly set to announce.
Aspartame – which is listed in the ingredients of the popular soft drinks brand – is set to be listed by the WHO's International Agency for Research on Cancer (IARC) as “possibly carcinogenic to humans” from next month, according to the Reuters news agency.
Since 1981, the Joint US Food and Agriculture/WHO Expert Committee on Food Additives (JECFA) regulator has said aspartame is safe to consume within accepted daily limits, which depends on a person's bodyweight.
It estimates that a nine-stone person would need to drink 12 to 36 cans of Diet Coke a day to see adverse affects from aspartame.
Experts responding to the Reuters have urged people to wait for the IARC's final announcement, emphasising that possibly being carcinogenic does not mean that a substance actually presents a risk to humans in normal circumstances.
According to the American Academy of Family Physicians, aspartame is one of the most studied sweeteners in the world – with more than 100 studies carried out into the product.
While the WHO is to list it as potentially cancer-causing, aspartame has not been listed as carcinogenic by the US National Cancer Institute.
In the UK, aspartame is approved for use. According to the NHS: "There have been reports that the use of sweeteners is linked to other health issues but the evidence base for this is limited," while Cancer Research UK has maintained that sweeteners do not cause cancer.
The sweetener is also listed as having other potential side-effects, with one study from Massachusetts General Hospital in 2022 suggesting aspartame could contribute to weight gain, although the NHS says using sweeteners rather than sugar can aide weight control.
“Aspartame consumption needs to be approached with caution due to the possible effects on neurobehavioral health," the authors of a 2017 study in Nutritional Neuroscience said, suggesting the sweetener could cause cognitive and behavioural problems including anxiety, depression and insomnia.
But aspartame, which is also listed as E-number E951, isn't just in fizzy drinks – it can be found in a number of other foods people consume on a regular basis.
Here's where else you can find the artificial sweetener:
Aspartame: What the experts say
Professor Kevin McConway, from the Open University, urged people to wait for the IARC's final announcement.
He also emphasised that possibly being carcinogenic does not mean that a substance actually presents a risk to humans in normal circumstances.
He said: "The IARC experts do not assess whether, in practice, a substance or exposure presents a cancer risk to people. Instead they assess whether it would ever be capable of presenting a risk, under any circumstances, even if the only harmful circumstances are really, really unlikely to occur."
Professor Oliver Jones, professor of chemistry at RMIT University in Melbourne, Australia, said: “We really need to wait and see the full IARC evaluation before we can make any firm conclusions. Without that we are really shooting in the dark. We don’t know what the terms of the assessment were, or what criteria they used to rule evidence in or out.
“It is also important to note that just because something may possibly cause cancer does not mean that it automatically does if you are exposed to it. The dose makes the poison.
Professor Tom Sanders, professor emeritus of nutrition and dietetics at King’s College London, said: “As far as I am aware there is no evidence from human prospective studies linking aspartame use to cancer and regulatory authorities have extensively reviewed the toxicological data and given aspartame a clean bill of health.”
Yahoo News has contacted Coca-Cola for comment.