Do artificial sweeteners cause cancer and are there other concerns?

Two reports on the sweetener aspartame came out this week, noting that some research has linked its consumption to liver cancer. This comes after the World Health Organization (WHO) advised most people to avoid most kinds of “non-sugar sweeteners”, after a 2022 review of the evidence found they don’t help with weight control long term and may cause diabetes, heart attacks and death.

Which sweeteners are the concern?

In May, the WHO said most sweeteners are problematic, both artificial ones, such as aspartame and saccharin, as well as ones made from plants, such as stevia. The exception is sweeteners made from sugar alcohols called polyols, which don’t fall under the “non-sugar sweeteners” umbrella and weren’t included in the review.

Does aspartame carry any extra risk?

Two separate international bodies this week issued reports on the long-used sweetener aspartame and they are seemingly somewhat contradictory. The WHO’s International Agency for Research on Cancer (IARC) has classified the substance as “possibly carcinogenic”, which sounds alarming, but actually means there is limited – and not convincing – evidence that it could be a cause of liver cancer.

A separate report, from the WHO and the Food and Agriculture Organization Joint Expert Committee on Food Additives concluded that there was no reason to change its existing recommendations on aspartame consumption. This advice says it is safe for people to have up to 40 milligrams of aspartame per kilogram of their body weight, which would be up to 14 cans of diet soft drinks a day for someone who weighs 70 kilograms.

“The findings of limited evidence of carcinogenicity in humans and animals, and of limited mechanistic evidence on how carcinogenicity may occur, underscore the need for more research to refine our understanding on whether consumption of aspartame poses a carcinogenic hazard,” said Mary Schubauer-Berigan at the IARC Monographs programme in a statement.

Would it be safer to avoid all sweeteners altogether?

The idea is that food and drinks with sweeteners help people reduce their sugar intake, as too much sugar is linked with higher weight, type 2 diabetes and heart disease. The trouble is that the evidence supporting this is mixed. Some short, randomised trials have found that consuming drinks with sweeteners instead of the full-sugar versions can reduce weight gain in children, but others have failed to show a benefit.

Population studies tend to show that sweetener consumption correlates with higher rates of diabetes and heart disease, but this could be because people are more likely to use sweeteners if they are heavier to start with, says Duane Mellor at Aston University in Birmingham, UK. The WHO says: “The available evidence suggests that use of non-sugar sweeteners does not confer any long-term benefit in reducing body fat.”

What about managing diabetes?

The WHO said its broad recommendations in May don’t apply to people who already have diabetes, because making recommendations for this group was outside the scope of the review and studies in people with diabetes weren’t included. That said, people with type 2 diabetes, where blood sugar can get too high, generally need to limit the amount of sugar they eat.

Are there any other concerns over sweeteners?

Some research has suggested unexpected harms from specific kinds of sweeteners, generally from small studies in people or those involving animals. For instance, last year, it was found that saccharin and sucralose may raise blood sugar levels. This year, preliminary evidence emerged that a common polyol sweetener called erythritol could promote blood clots, although the polyols weren’t included in the WHO’s review anyway.

Findings such as these contradict initial assumptions that sweeteners are biologically inert. Nevertheless, current official health advice in most countries says people should choose artificial sweeteners over sugar.

So, do others agree we should ditch sweeteners?

It’s complicated. Researchers say sweeteners still have their use, despite the WHO advising against them. “The recommendation could have been a bit more nuanced in acknowledging the potential utility of non-sugar sweeteners to support short-term weight loss when used judiciously,” says Allison Sylvetsky at The George Washington University in Washington DC.

You also may find it difficult to avoid sweeteners, as many foods and drinks now contain them without necessarily being marketed as diet products. This is especially true in countries such as the UK, South Africa and Portugal where “sugar taxes” have nudged drink manufacturers into using more sweeteners. But that isn’t necessarily a bad thing, says Mellor. “If you’re going to consume a soft drink, it’s better to switch to one with less sugar and more sweeteners,” he says. “But the perfect solution is going for water.”

What happens now?

Countries aren’t obliged to follow WHO recommendations, but its reports may carry weight when national policies are being set. Because of the uncertainties in the evidence, the WHO says these recommendations are “conditional”, meaning that they may need to be implemented differently by different countries. Some nations may just ignore the WHO guidelines, says Thomas Sanders at King’s College London. “It’s going to cause some ructions.”