There has been a flurry of media interest in the potential carcinogenicity of the artificial sweetener aspartame in recent weeks. But what is the truth behind the story, and should we be worried? Rod Tucker takes a closer look, in our Review series.

Aspartame was produced by James Schlatter, in 1965, while researching anti-ulcer treatments. In a moment of serendipity (and contrary to safety regulations) Schlatter licked the compound off his fingers, and realised the compound was incredibly sweet.

Aspartame was subsequently designated as a food additive, and produced commercially from 1981. It is between 180 and 200 times sweeter than sucrose, and was quickly seen as a suitable alternative to sugar for people with diabetes.

Today, aspartame is found in a wide range of food and drink products, although whether or not the replacement of sugar with artificial sweeteners has health benefits remains a moot point. In fact, a recent review on the topic suggested that artificial sweeteners increase the risk of cardiovascular disease and death.

Do artificial sweeteners like aspartame increase the risk of cancer? In a 2004 review of evidence, the authors concluded that it does not seem that artificial sweeteners cause cancer. However, these findings came with an important caveat that because artificial sweeteners are widely used in many foods, it is almost impossible to assign a carcinogenic risk to a single substance.

Much of the evidence related to the cancer risk of aspartame does suggest that its use does not lead to the development of cancer.

While this is reassuring, an inherent problem is that type of data used to inform this view is derived from self-administered questionnaires collected at a single point in time. In other words, it is not possible to examine the impact of longer-term exposure and cancer risk.

One solution to this limitation is to prospectively examine use of artificial sweeteners over time and this was exactly what was done in a recent French study. The French team collected information on artificial sweetener intake at the start of the study and then every year. After eight years of follow-up, the results offered a rather different interpretation: intake of aspartame was linked to a 15% higher risk of cancer. An addition, a subsequent re-analysis of rodent carcinogenicity test results for aspartame published in 2021, concluded that aspartame is a carcinogen in rodents and that prenatal exposure increased cancer risk in their offspring.

What does the most recent information suggest?

In June 2023, the International Agency for Research on Cancer (IARC) declared that aspartame as ‘possibly carcinogenic to humans,’ although recognised that this was based on limited human evidence. But a second report, published at the same time by the World Health Organization and Food and Agriculture Organization’s Joint Expert Committee on Food Additives (JECFA), re-affirmed the acceptable safety limit for aspartame intake of 40 mg/kg of body weight.

In a sense, while both committees have taken another look at the same evidence, IARC suggests aspartame is a potentially carcinogenic, whereas JECFA didn’t see the need to change its recommendation at this time, presumably feeling that there isn’t a greater cancer risk from the sweetener.

What are we to make of all this? It’s important to understand that the two committees were not reviewing the same data and arriving at a different conclusion. IARC looked at the possible hazard from aspartame, i.e., are there circumstances in which aspartame intake would increase the risk of cancer. In contrast, JECFA looked at the health hazards, i.e., the safety of consuming aspartame. They felt that aspartame does not pose a hazard to health, provided daily consumption does not exceed 40 mg/kg.

How much diet cola, for example, would someone need to drink to reach that daily limit? The amount of aspartame in foods is rarely provided on labels, but a study from 1992 found that a typical 12 oz can (roughly 330mL) of cola contained 184 mg of aspartame.

As a result, a typical 70 kg adult would therefore need to consume around 15 cans of cola per day to reach the safety limit (although this figure doesn’t account for intake from other dietary sources).

Although healthy eating advice does not advocate consumption of either sugary drinks or those containing artificial sweeteners, pharmacists can reassure their patients, if asked, that while there has been much recent media interest in aspartame, they shouldn’t be overly concerned and that really, on available evidence, it does seem to be a fuss over nothing.