Earlier this month, aspartame – the sugar substitute found in Diet Coke – was added to the World Health Organization’s list of more than 300 substances that ‘probably’ cause cancer.
The WHO notes that the sweetener, which is also found in a wide range of foods, is still safe to consume and that the average adult would need to consume between 9 and 14 cans of Diet Coke a day to exceed the recommended limit. Even then, any risk was based on ‘limited scientific evidence’, including decades-old animal studies.
Scientists were quick to point out that the results of this study, which involved feeding large amounts of aspartame to lab rats, were widely disputed.
Others tried to reassure the public that there was no cause for panic: after all, the same list of ‘probable’ carcinogens included aloe vera – the ubiquitous plant extract added to everyday skin care products, supplements and even mouthwash and toothpaste.
No doubt, this was intended to show how much of a non-issue it was. But, in some cases, the claim has only added to the concern.
Aloe vera (pictured), the ubiquitous plant extract added to everyday skin care products, supplements and even mouthwash and toothpaste, is on the WHO’s list of ‘probable’ carcinogens
‘Is aloe vera carcinogenic?’ wrote a concerned Twitter user.
‘Surprised to see aloe vera on the same list as lead, welding fumes and engine exhaust,’ commented another. ‘Does that mean I can’t use it for sunburn?’ asked a third.
So what are the ‘risks’ of aloe vera – and should we be concerned that it’s on the list of ‘probable’ carcinogens? The short answer, according to toxicology experts, is no.
The cactus-like aloe plant has been used in traditional medicine for centuries, with the ancient Greeks and Romans applying the clear inner poultice to wounds.
Today, aloe vera extract has found its way into almost every type of skin care product – from sunburn-relief gels and moisturizers to shampoos, soaps and even deodorants.
The global aloe vera extract market is worth around £1.2 billion – demand is growing every year.
However, there may be reasons for caution if you intend to consume it rather than just rubbing it into the skin. There is some evidence that a certain component of aloe – the yellow liquid sap found inside the leaves, between the outer ‘rind’ and the inner pulp, known as aloe vera latex – can cause problems if eaten.
Researchers studying the toxic effects of aloe vera in 2013 exposed mice to different concentrations of ‘whole-leaf extract of aloe vera’, which contains aloe vera latex, for two years. After two years feeding some mice developed a rare intestinal tumor at high concentrations. Animals fed low concentrations of aloe vera liquid did not develop these tumors.
Scientists believe that compounds in aloe vera latex known as anthraquinones – which have a laxative effect and irritate the digestive system – are responsible. As well as skin products, aloe vera extracts are also found in health food supplements – claiming to do everything from ‘detoxing’ to improving digestion – and beverages.
In light of the 2013 findings, the European Food Safety Authority issued a warning advising against ‘long-term use and consumption. [of anthraquinone-containing supplements] At higher doses, due to potential safety concerns’.
Earlier this month, aspartame – the sugar substitute found in Diet Coke – was added to the World Health Organization’s list of more than 300 substances that ‘probably’ cause cancer.
And in 2019, it recommended banning some aloe vera extracts known to contain the most harmful anthraquinone. Around the same time it was added to the WHO’s list of ‘probable’ cancer causes.
Alan Bubis, emeritus professor of toxicology at Imperial College London, said: ‘This is a rare type of tumor that they found in the 2013 study. [investigating the effect of aloe vera on rats]Which means they were pretty sure it was directly related to the substance the rats ate.
‘Other studies have also found evidence that anthraquinone damages the DNA of cells that can lead to cancer.’
Interestingly, the same study found that mice fed the same water did not develop tumors. Professor Bubis said: ‘There is no evidence of harmful effects in humans – but the research we have done means the risk cannot be ruled out and that is why it is on the “probable” list.’
The WHO carcinogen list, developed by the International Agency for Research on Cancer, is divided into categories.
Groups 1 and 2A are substances that are known to be carcinogenic to humans or that are ‘probably’ carcinogenic, such as smoking, processed meats, asbestos, red meat and acrylamide – a compound formed when foods are ‘browned’ at high temperatures.
Group 2B is ‘probable’ risk, as there is some but not strong evidence of a cancer risk. An example of this is when evidence is drawn only from animal studies, such as with aloe vera latex.
Aloe vera supplements and drinks sold in UK shops are approved by the government’s Food Standards Agency, so should contain safe levels of anthraquinone, Professor Bubis added.
But those who grow their own aloe vera — and scoop out the inner part of the leaf to add smoothness — may want to consider the danger.
In high concentrations, aloe vera, taken orally, can trigger diarrhea and cramps.
There have also been isolated case reports of heavy bleeding during surgery and kidney and liver problems in patients taking aloe vera preparations. There are also suggestions that supplements may interfere with certain medications, such as blood thinners.
‘It’s a myth that “natural” is always safe or good for you,’ says Professor Bubis. ‘Some of the most toxic substances come from natural sources. Having said that, my main concern about health food products is not safety, it’s that there is little convincing evidence for the positive effects many of them claim.’
…and should we avoid kimchi?
Trendy pickled Asian vegetables – such as Korean kimchi – are also on the WHO list as ‘probably’ causing cancer.
It’s billed as a gut-friendly boost to any meal.
But trendy pickled Asian vegetables – such as Korean kimchi – are also on the WHO’s list of ‘probably’ cancer-causing foods.
These dishes are made by adding a lot of salt to the vegetables, as well as sugar, spices and fish sauce. The mixture is then left to ferment for several days, releasing lactic acid.
This acid is said to feed the healthy bacteria in our gut, leading to many benefits.
But studies have shown that countries where pickled vegetables are a dietary staple, such as Korea and Japan, have higher rates of stomach and esophageal cancer than countries where they eat less. A 2012 review of 60 studies found that regular consumption of pickled vegetables increased the risk of stomach cancer by 50 percent, compared to those who ate little or none.
This is thought to be due to the salt content which, during fermentation, converts nitrates in the vegetables to nitrites – which are linked to cancer. But pickling using vinegar and less salt is thought to interfere with nitrates and is not associated with the same cancer risk.
The researchers also say the link is unclear, as most of the evidence is based on observations rather than direct cause and effect. As the evidence is weak, it is only a ‘probable’ reason and nothing more definite.