Why has WHO declared that aspartame is a possible carcinogen?

Artificial sweetener widely used in diet fizzy drinks, chewing gum and low-sugar breakfast cereals and yoghurts

Aspartame is used in thousands of products, including Diet Coke. Photograph: Yui Mok/PA Wire

A World Health Organisation (WHO) agency said on Thursday that aspartame, an artificial sweetener widely used in diet drinks and low-sugar foods, could possibly cause cancer. Here’s a guide to what you need to know about this development.

Q: There seems to be some confusion between two different WHO agencies as to the risk of consuming artificial sweetener. Can you explain what’s going on?

A: The International Agency for Research on Cancer (IARC) said it based its conclusion that aspartame was a possible carcinogen on limited evidence from three observational studies of humans that the agency said linked consumption of artificially sweetened beverages to an increase in cases of liver cancer. A second WHO committee, however, stuck with its previous declaration that there is a known safe level of aspartame consumption. The Food and Agricultural Organisation’s (FAO) Joint Expert Committee on Food Additives, retained its advice that it is safe for a person to consume up to 40mg for every kg of body weight each day.

Q: What does that mean in practice?

A: It means that a person weighing 70kg would need to drink more than about a dozen cans of diet soft drink a day to exceed the daily guideline.

Q: Are all artificial sweeteners now under suspicion?

A: No, just aspartame, which has been in use for over thirty years. Aspartame is used in thousands of products including diet fizzy drinks, yoghurts, ice cream, breakfast cereals and chewing gum. It is also used to sweeten various pharmaceutical products. The concern is at a low level of suspicion, however, with the IARC having two more serious cancer-causing categories. These are “probably carcinogenic to humans” and “carcinogenic to humans”.

Q: What should you do if you are a consumer of high amounts of aspartame?

A: People who consume high amounts of aspartame in diet drinks should consider switching to water or other unsweetened drinks, said Dr Francesco Branca, director of the WHO’s Department of Nutrition and Food Safety. But “our results do not indicate that occasional consumption should pose a risk to most”, he said.

Q: I had a heart attack recently and I was advised to give up sugar and salt. I have been using an artificial sweetener in my tea. What should I do now?

A: If you have been using aspartame, then you may wish to switch to an alternative artificial sweetener such as Splenda or Stevia. However, even if you drink a lot of tea, you are unlikely to be consuming in excess of the daily limit of aspartame suggested by the FAO.

Muiris Houston

Dr Muiris Houston

Dr Muiris Houston is medical journalist, health analyst and Irish Times contributor